rustial_engine/layers/

vector_layer.rs

//! Vector data layer -- geographic feature tessellation and terrain draping.
//!
//! [`VectorLayer`] holds a [`FeatureCollection`] and a [`VectorStyle`],
//! and provides two core operations consumed by the per-frame engine
//! update loop in [`MapState::update_layers`](crate::MapState):
//!
//! 1. **Terrain draping** ([`drape_on_terrain`](VectorLayer::drape_on_terrain))
//!    -- walk every vertex in the feature collection and set its altitude
//!    to the terrain elevation at that coordinate.  No-op when terrain is
//!    disabled or elevation data is unavailable.
//!
//! 2. **Tessellation** ([`tessellate`](VectorLayer::tessellate)) -- convert
//!    the geographic features into GPU-ready triangle meshes stored in
//!    [`VectorMeshData`].
//!
//! Rustial's style/runtime layer families such as `fill`, `line`, `circle`,
//! `heatmap`, `symbol`, and `fill-extrusion` are all currently lowered onto
//! this shared engine primitive via [`VectorRenderMode`].

use crate::camera_projection::CameraProjection;
use crate::expression::{ExprEvalContext, Expression};
use crate::geometry::{Feature, FeatureCollection, Geometry};
use crate::layer::{Layer, LayerId};
use crate::query::feature_id_for_feature;
use crate::symbols::{
    SymbolAnchor, SymbolCandidate, SymbolIconTextFit, SymbolPlacement, SymbolTextJustify,
    SymbolTextTransform, SymbolWritingMode,
};
use crate::terrain::TerrainManager;
use crate::tessellator;
use crate::visualization::ColorRamp;
use rustial_math::{GeoCoord, TileId, WorldCoord};
use std::any::Any;
use std::sync::Arc;

// ---------------------------------------------------------------------------
// Constants
// ---------------------------------------------------------------------------

/// Approximate meters per degree of latitude at the equator.
///
/// Used to convert pixel-space stroke widths into a geographic offset
/// for the stroke tessellator, and to size point-marker quads.  This
/// is a rough approximation; proper screen-to-world conversion
/// requires the camera's meters-per-pixel, which is not available at
/// the layer level.  A future improvement would pass `meters_per_pixel`
/// into `tessellate()`.
const METERS_PER_DEGREE: f64 = 111_319.49;
const DEGREES_PER_PIXEL_APPROX: f64 = 0.00001;
const METERS_PER_PIXEL_APPROX: f64 = METERS_PER_DEGREE * DEGREES_PER_PIXEL_APPROX;
const DEFAULT_CIRCLE_SEGMENTS: usize = 20;

// ---------------------------------------------------------------------------
// Pattern image
// ---------------------------------------------------------------------------

/// An RGBA8 pattern image used for fill-pattern and line-pattern rendering.
///
/// The image is stored as a flat `Vec<u8>` in row-major RGBA order
/// (`width × height × 4` bytes).  Typically shared via `Arc<PatternImage>`
/// so the same image can be referenced by the style, the engine mesh
/// data, and the renderer without cloning pixel data.
#[derive(Debug, Clone)]
pub struct PatternImage {
    /// Image width in pixels.
    pub width: u32,
    /// Image height in pixels.
    pub height: u32,
    /// Pixel data in RGBA8 format (`width * height * 4` bytes).
    pub data: Vec<u8>,
}

impl PatternImage {
    /// Create a new pattern image from raw RGBA8 pixel data.
    ///
    /// # Panics
    ///
    /// Panics if `data.len() != width * height * 4`.
    pub fn new(width: u32, height: u32, data: Vec<u8>) -> Self {
        assert_eq!(
            data.len(),
            (width * height * 4) as usize,
            "RGBA8 data length must be width × height × 4"
        );
        Self { width, height, data }
    }
}

/// High-level vector rendering family.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub enum VectorRenderMode {
    /// Legacy generic tessellation that renders polygons, lines, and points.
    #[default]
    Generic,
    /// Polygon fills.
    Fill,
    /// Line-only rendering.
    Line,
    /// Point circles.
    Circle,
    /// Point heatmap blobs.
    Heatmap,
    /// Polygon extrusion into simple 3D prisms.
    FillExtrusion,
    /// Basic point symbols rendered as simple haloed markers.
    Symbol,
}

/// Line cap style — how the endpoints of a line are drawn.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub enum LineCap {
    /// Flat cut at the endpoint (default).
    #[default]
    Butt,
    /// Semicircular cap extending half-width beyond the endpoint.
    Round,
    /// Square cap extending half-width beyond the endpoint.
    Square,
}

/// Line join style — how adjacent segments of a line are connected.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub enum LineJoin {
    /// Sharp corner extended along the bisector, falling back to bevel
    /// when the miter ratio exceeds [`VectorStyle::miter_limit`].
    #[default]
    Miter,
    /// Flat diagonal cut at the outer bend.
    Bevel,
    /// Rounded arc at the outer bend.
    Round,
}

/// Tile-owned provenance for a vector feature.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct FeatureProvenance {
    /// Source-layer name, when known.
    pub source_layer: Option<String>,
    /// Actual tile that supplied this feature.
    pub source_tile: Option<TileId>,
}

/// Style parameters for rendering a vector layer.
#[derive(Debug, Clone)]
pub struct VectorStyle {
    /// Active render family.
    pub render_mode: VectorRenderMode,
    /// Fill colour (RGBA, 0--1 range).
    pub fill_color: [f32; 4],
    /// Stroke (outline) colour (RGBA, 0--1 range).
    pub stroke_color: [f32; 4],
    /// Stroke width in pixels.
    pub stroke_width: f32,
    /// Point/circle radius in pixels.
    pub point_radius: f32,
    /// Line cap style.
    pub line_cap: LineCap,
    /// Line join style.
    pub line_join: LineJoin,
    /// Miter limit ratio — when the miter length exceeds `miter_limit *
    /// stroke_width`, a miter join falls back to bevel.  Default 2.0
    /// (matching MapLibre / Mapbox).
    pub miter_limit: f32,
    /// Optional dash pattern `[dash_length, gap_length, …]` in pixels.
    pub dash_array: Option<Vec<f32>>,
    /// Heatmap radius in pixels.
    pub heatmap_radius: f32,
    /// Heatmap intensity multiplier.
    pub heatmap_intensity: f32,
    /// Extrusion base height in meters.
    pub extrusion_base: f32,
    /// Extrusion height in meters.
    pub extrusion_height: f32,
    /// Symbol size in pixels.
    pub symbol_size: f32,
    /// Symbol halo colour.
    pub symbol_halo_color: [f32; 4],
    /// Feature property used for text labels.
    pub symbol_text_field: Option<String>,
    /// Optional icon image id for point symbols.
    pub symbol_icon_image: Option<String>,
    /// Font stack used for glyph dependency requests.
    pub symbol_font_stack: String,
    /// Collision padding in pixels.
    pub symbol_padding: f32,
    /// Shared overlap fallback for simplified callers.
    ///
    /// Mapbox and MapLibre distinguish text and icon overlap flags. The engine
    /// keeps this field as a shared default for existing call sites, while the
    /// more specific text/icon flags below let symbol candidates apply closer
    /// spec behavior.
    pub symbol_allow_overlap: bool,
    /// Whether text is allowed to overlap other placed symbols.
    pub symbol_text_allow_overlap: bool,
    /// Whether icons are allowed to overlap other placed symbols.
    pub symbol_icon_allow_overlap: bool,
    /// Whether text may be dropped while keeping the icon.
    pub symbol_text_optional: bool,
    /// Whether the icon may be dropped while keeping the text.
    pub symbol_icon_optional: bool,
    /// Whether text may be placed without blocking later symbols.
    pub symbol_text_ignore_placement: bool,
    /// Whether icons may be placed without blocking later symbols.
    pub symbol_icon_ignore_placement: bool,
    /// Default anchor when variable anchors are not in use.
    pub symbol_text_anchor: SymbolAnchor,
    /// Effective horizontal justification for the current label.
    pub symbol_text_justify: SymbolTextJustify,
    /// Text transformation applied before measurement and placement.
    pub symbol_text_transform: SymbolTextTransform,
    /// Maximum point-label width in symbol-size units before wrapping.
    ///
    /// This is the engine's simplified `text-max-width` representation. It is
    /// currently used to estimate wrapped placeholder text boxes for point
    /// labels, which improves collision and sizing behavior before full glyph
    /// shaping is in place.
    pub symbol_text_max_width: Option<f32>,
    /// Preferred line height for wrapped text in text-size units.
    ///
    /// The engine uses this in its simplified wrapped text-box estimate so
    /// placeholder label height follows the style more closely even before full
    /// glyph shaping is implemented.
    pub symbol_text_line_height: Option<f32>,
    /// Extra spacing between adjacent glyphs in text-size units.
    ///
    /// The engine applies this to its placeholder text width estimate so label
    /// collisions and wrapping react to `text-letter-spacing` before full glyph
    /// shaping exists.
    pub symbol_text_letter_spacing: Option<f32>,
    /// Icon sizing mode relative to label text.
    pub symbol_icon_text_fit: SymbolIconTextFit,
    /// Padding applied when fitting the icon around text.
    pub symbol_icon_text_fit_padding: [f32; 4],
    /// Placement priority for symbol ordering.
    ///
    /// Lower sort keys are placed first, matching Mapbox and MapLibre's
    /// `symbol-sort-key` semantics. `None` preserves source order when the
    /// style does not request explicit symbol ordering.
    pub symbol_sort_key: Option<f32>,
    /// Preferred variable anchors in priority order.
    pub symbol_anchors: Vec<SymbolAnchor>,
    /// Whether symbols are anchored on points or along lines.
    pub symbol_placement: SymbolPlacement,
    /// Preferred spacing between repeated line-placed symbols in pixels.
    ///
    /// Mapbox and MapLibre interpret this during tile-space symbol layout.
    /// The engine currently uses it as an approximate world-space spacing for
    /// repeated line anchors until full line-shaped symbol layout is in place.
    pub symbol_spacing: f32,
    /// Maximum cumulative turn angle tolerated for a line-placed label.
    ///
    /// The current implementation applies this as a simplified readability
    /// check over the retained line window around each anchor. It is not yet a
    /// full reproduction of Mapbox or MapLibre's sliding-window angle logic,
    /// but it prevents labels from being emitted on the sharpest bends.
    pub symbol_max_angle: f32,
    /// Whether line-placed text should be flipped to remain upright.
    ///
    /// Mapbox and MapLibre use this to avoid upside-down line labels. The
    /// engine currently applies it by normalizing line-anchor rotation into an
    /// upright range before placement.
    pub symbol_keep_upright: bool,
    /// Radial text offset measured in symbol-size units.
    ///
    /// The full style spec defines this in EM-like text units. The engine uses
    /// the current symbol size as the scale factor so anchored labels can move
    /// outward in the requested direction without waiting for full glyph
    /// shaping metrics.
    pub symbol_text_radial_offset: Option<f32>,
    /// Explicit per-anchor offsets for variable anchor placement.
    ///
    /// This is the engine's simplified representation of
    /// `text-variable-anchor-offset`. Values are stored in symbol-size units and
    /// resolved for the selected anchor during placement.
    pub symbol_variable_anchor_offsets: Option<Vec<(SymbolAnchor, [f32; 2])>>,
    /// Writing mode for symbol text.
    pub symbol_writing_mode: SymbolWritingMode,
    /// Pixel-space symbol offset.
    pub symbol_offset: [f32; 2],
    /// Fill-layer pixel translate offset `[tx, ty]`.
    pub fill_translate: [f32; 2],
    /// Fill-layer opacity (separate from vertex alpha).
    pub fill_opacity: f32,
    /// Whether fill edges should be antialiased.
    pub fill_antialias: bool,
    /// Optional distinct outline color. When `None`, outline uses `stroke_color`.
    pub fill_outline_color: Option<[f32; 4]>,

    /// Optional fill pattern image.
    ///
    /// When set, the fill is rendered with a repeating pattern texture
    /// instead of a solid colour.  The pattern repeats in world space
    /// with one pattern pixel mapping to approximately one meter,
    /// matching MapLibre / Mapbox `fill-pattern` semantics.
    pub fill_pattern: Option<Arc<PatternImage>>,

    /// Optional line pattern image.
    ///
    /// When set, the line is rendered with a repeating pattern texture
    /// instead of a solid colour.  The pattern maps along the line
    /// centreline (U axis, distance / pattern width) and across the line
    /// width (V axis, 0 at left edge → 1 at right edge), matching
    /// MapLibre / Mapbox `line-pattern` semantics.
    pub line_pattern: Option<Arc<PatternImage>>,

    // -- Data-driven expression overrides ---------------------------------

    /// Optional data-driven width expression.
    ///
    /// When present and [`Expression::is_data_driven`] returns `true`,
    /// [`VectorLayer::tessellate`] evaluates the expression per feature
    /// instead of using the single `stroke_width` value for every feature.
    pub width_expr: Option<Expression<f32>>,
    /// Optional data-driven stroke-color expression.
    ///
    /// Same semantics as `width_expr`: when data-driven, colour is resolved
    /// per feature during tessellation.
    pub stroke_color_expr: Option<Expression<[f32; 4]>>,
    /// Zoom level captured at style-evaluation time.
    ///
    /// Needed to build a per-feature [`ExprEvalContext`] during tessellation
    /// so that zoom-dependent stops still resolve correctly.
    pub eval_zoom: f32,

    // -- Line gradient -------------------------------------------------------

    /// Optional colour ramp evaluated along the polyline centreline.
    ///
    /// When set, the tessellator overrides per-vertex colours with the
    /// gradient evaluated at each vertex's normalized distance `[0, 1]`
    /// along the feature.  This replicates MapLibre / Mapbox's
    /// `line-gradient` property.
    pub line_gradient: Option<ColorRamp>,
}

impl Default for VectorStyle {
    fn default() -> Self {
        Self {
            render_mode: VectorRenderMode::Generic,
            fill_color: [0.2, 0.5, 0.8, 0.5],
            stroke_color: [0.0, 0.0, 0.0, 1.0],
            stroke_width: 2.0,
            point_radius: 6.0,
            line_cap: LineCap::Butt,
            line_join: LineJoin::Miter,
            miter_limit: 2.0,
            dash_array: None,
            heatmap_radius: 18.0,
            heatmap_intensity: 1.0,
            extrusion_base: 0.0,
            extrusion_height: 30.0,
            symbol_size: 10.0,
            symbol_halo_color: [1.0, 1.0, 1.0, 0.85],
            symbol_text_field: None,
            symbol_icon_image: None,
            symbol_font_stack: "Noto Sans Regular".into(),
            symbol_padding: 2.0,
            symbol_allow_overlap: false,
            symbol_text_allow_overlap: false,
            symbol_icon_allow_overlap: false,
            symbol_text_optional: false,
            symbol_icon_optional: false,
            symbol_text_ignore_placement: false,
            symbol_icon_ignore_placement: false,
            symbol_text_anchor: SymbolAnchor::Center,
            symbol_text_justify: SymbolTextJustify::Auto,
            symbol_text_transform: SymbolTextTransform::None,
            symbol_text_max_width: None,
            symbol_text_line_height: None,
            symbol_text_letter_spacing: None,
            symbol_icon_text_fit: SymbolIconTextFit::None,
            symbol_icon_text_fit_padding: [0.0, 0.0, 0.0, 0.0],
            symbol_sort_key: None,
            symbol_anchors: vec![SymbolAnchor::Center],
            symbol_placement: SymbolPlacement::Point,
            symbol_spacing: 250.0,
            symbol_max_angle: 45.0,
            symbol_keep_upright: true,
            symbol_text_radial_offset: None,
            symbol_variable_anchor_offsets: None,
            symbol_writing_mode: SymbolWritingMode::Horizontal,
            symbol_offset: [0.0, 0.0],
            fill_translate: [0.0, 0.0],
            fill_opacity: 1.0,
            fill_antialias: true,
            fill_outline_color: None,
            fill_pattern: None,
            line_pattern: None,
            width_expr: None,
            stroke_color_expr: None,
            eval_zoom: 0.0,
            line_gradient: None,
        }
    }
}

impl VectorStyle {
    /// Convenience constructor for fill rendering.
    pub fn fill(fill_color: [f32; 4], outline_color: [f32; 4], outline_width: f32) -> Self {
        Self {
            render_mode: VectorRenderMode::Fill,
            fill_color,
            stroke_color: outline_color,
            stroke_width: outline_width,
            ..Self::default()
        }
    }

    /// Fill rendering with a repeating pattern texture.
    ///
    /// The pattern overrides `fill_color` — the fragment shader samples
    /// the pattern image instead of using a solid colour.
    pub fn fill_pattern(pattern: Arc<PatternImage>) -> Self {
        Self {
            render_mode: VectorRenderMode::Fill,
            fill_pattern: Some(pattern),
            ..Self::default()
        }
    }

    /// Line rendering with a repeating pattern texture.
    ///
    /// The pattern maps along the line centreline and across its width.
    /// The fragment shader samples the pattern image instead of using a
    /// solid colour, matching MapLibre / Mapbox `line-pattern` semantics.
    pub fn line_pattern(width: f32, pattern: Arc<PatternImage>) -> Self {
        Self {
            render_mode: VectorRenderMode::Line,
            stroke_width: width,
            line_pattern: Some(pattern),
            ..Self::default()
        }
    }

    /// Convenience constructor for line rendering.
    pub fn line(color: [f32; 4], width: f32) -> Self {
        Self {
            render_mode: VectorRenderMode::Line,
            stroke_color: color,
            stroke_width: width,
            ..Self::default()
        }
    }

    /// Line rendering with explicit cap, join, and miter limit.
    pub fn line_styled(
        color: [f32; 4],
        width: f32,
        cap: LineCap,
        join: LineJoin,
        miter_limit: f32,
        dash_array: Option<Vec<f32>>,
    ) -> Self {
        Self {
            render_mode: VectorRenderMode::Line,
            stroke_color: color,
            stroke_width: width,
            line_cap: cap,
            line_join: join,
            miter_limit,
            dash_array,
            ..Self::default()
        }
    }

    /// Line rendering with a colour gradient along the polyline.
    ///
    /// The gradient overrides `color` — per-vertex colours are computed
    /// from the `ColorRamp` at each vertex's normalised distance along
    /// the line.
    pub fn line_gradient(width: f32, ramp: ColorRamp) -> Self {
        Self {
            render_mode: VectorRenderMode::Line,
            stroke_color: [1.0, 1.0, 1.0, 1.0],
            stroke_width: width,
            line_gradient: Some(ramp),
            ..Self::default()
        }
    }

    /// Convenience constructor for point circles.
    pub fn circle(color: [f32; 4], radius: f32, stroke_color: [f32; 4], stroke_width: f32) -> Self {
        Self {
            render_mode: VectorRenderMode::Circle,
            fill_color: color,
            point_radius: radius,
            stroke_color,
            stroke_width,
            ..Self::default()
        }
    }

    /// Convenience constructor for heatmap blobs.
    pub fn heatmap(color: [f32; 4], radius: f32, intensity: f32) -> Self {
        Self {
            render_mode: VectorRenderMode::Heatmap,
            fill_color: color,
            heatmap_radius: radius,
            heatmap_intensity: intensity,
            ..Self::default()
        }
    }

    /// Convenience constructor for polygon extrusion.
    pub fn fill_extrusion(color: [f32; 4], base: f32, height: f32) -> Self {
        Self {
            render_mode: VectorRenderMode::FillExtrusion,
            fill_color: color,
            extrusion_base: base,
            extrusion_height: height,
            ..Self::default()
        }
    }

    /// Convenience constructor for basic symbol markers.
    pub fn symbol(color: [f32; 4], halo_color: [f32; 4], size: f32) -> Self {
        Self {
            render_mode: VectorRenderMode::Symbol,
            fill_color: color,
            symbol_halo_color: halo_color,
            symbol_size: size,
            ..Self::default()
        }
    }

    /// Compute a lightweight `u64` fingerprint of the fields that affect
    /// [`VectorLayer::tessellate`] output.
    ///
    /// Two styles that produce identical tessellation results will have the
    /// same fingerprint. The hash is cheap (a few dozen field reads through
    /// the default hasher) and is used by the sync-path vector bucket cache
    /// to detect style changes without requiring `PartialEq` on
    /// `VectorStyle`.
    pub fn tessellation_fingerprint(&self) -> u64 {
        use std::hash::{Hash, Hasher};
        let mut h = std::collections::hash_map::DefaultHasher::new();
        // render_mode
        std::mem::discriminant(&self.render_mode).hash(&mut h);
        // colors and widths that feed into vertex output
        self.fill_color.iter().for_each(|v| v.to_bits().hash(&mut h));
        self.stroke_color.iter().for_each(|v| v.to_bits().hash(&mut h));
        self.stroke_width.to_bits().hash(&mut h);
        self.point_radius.to_bits().hash(&mut h);
        self.heatmap_radius.to_bits().hash(&mut h);
        self.heatmap_intensity.to_bits().hash(&mut h);
        self.extrusion_base.to_bits().hash(&mut h);
        self.extrusion_height.to_bits().hash(&mut h);
        self.symbol_size.to_bits().hash(&mut h);
        self.symbol_halo_color.iter().for_each(|v| v.to_bits().hash(&mut h));
        self.fill_translate.iter().for_each(|v| v.to_bits().hash(&mut h));
        self.fill_opacity.to_bits().hash(&mut h);
        self.fill_antialias.hash(&mut h);
        if let Some(ref c) = self.fill_outline_color {
            c.iter().for_each(|v| v.to_bits().hash(&mut h));
        }
        // Data-driven state: when an expression is data-driven, the
        // tessellation output depends on per-feature properties, making
        // the fingerprint also depend on the zoom level (which affects
        // interpolated stops).
        let has_dd_width = self.width_expr.as_ref().is_some_and(|e| e.is_data_driven());
        let has_dd_color = self.stroke_color_expr.as_ref().is_some_and(|e| e.is_data_driven());
        has_dd_width.hash(&mut h);
        has_dd_color.hash(&mut h);
        if has_dd_width || has_dd_color {
            self.eval_zoom.to_bits().hash(&mut h);
        }
        h.finish()
    }

    /// Whether line width is data-driven (varies per feature).
    #[inline]
    pub fn is_width_data_driven(&self) -> bool {
        self.width_expr.as_ref().is_some_and(|e| e.is_data_driven())
    }

    /// Whether stroke color is data-driven (varies per feature).
    #[inline]
    pub fn is_stroke_color_data_driven(&self) -> bool {
        self.stroke_color_expr.as_ref().is_some_and(|e| e.is_data_driven())
    }

    /// Evaluate stroke width for a specific feature's properties.
    ///
    /// Returns `self.stroke_width` when no data-driven expression is set.
    pub fn evaluate_width(&self, feature: &Feature) -> f32 {
        match &self.width_expr {
            Some(expr) if expr.is_data_driven() => {
                let ctx = ExprEvalContext::with_feature(self.eval_zoom, &feature.properties);
                expr.evaluate_with_properties(&ctx)
            }
            _ => self.stroke_width,
        }
    }

    /// Evaluate stroke color for a specific feature's properties.
    ///
    /// Returns `self.stroke_color` when no data-driven expression is set.
    pub fn evaluate_stroke_color(&self, feature: &Feature) -> [f32; 4] {
        match &self.stroke_color_expr {
            Some(expr) if expr.is_data_driven() => {
                let ctx = ExprEvalContext::with_feature(self.eval_zoom, &feature.properties);
                expr.evaluate_with_properties(&ctx)
            }
            _ => self.stroke_color,
        }
    }
}

#[derive(Clone, Copy)]
struct LinePlacementAnchor {
    coord: GeoCoord,
    rotation_rad: f32,
    distance: f64,
}

// ---------------------------------------------------------------------------
// VectorMeshData
// ---------------------------------------------------------------------------

/// Per-instance data for SDF circle rendering.
///
/// Each circle is rendered as a screen-aligned quad by the GPU.  The
/// fragment shader evaluates an SDF to produce anti-aliased circles with
/// optional stroke.
#[derive(Debug, Clone, Copy, Default)]
pub struct CircleInstanceData {
    /// Circle centre in world space `[x, y, z]` (f64 for precision).
    pub center: [f64; 3],
    /// Circle radius in world-space meters.
    pub radius: f32,
    /// Fill colour `[r, g, b, a]`.
    pub color: [f32; 4],
    /// Stroke colour `[r, g, b, a]`.
    pub stroke_color: [f32; 4],
    /// Stroke width in world-space meters.
    pub stroke_width: f32,
    /// Blur amount (0 = hard edge, 1 = fully soft).
    pub blur: f32,
}

/// CPU-side mesh data for vector rendering, ready for GPU upload.
///
/// Produced by [`VectorLayer::tessellate`] and consumed by renderers.
/// One instance per visible vector layer per frame.
///
/// All positions are in **Web Mercator world space** (f64 for precision).
/// The renderer converts them to camera-relative f32 before uploading.
#[derive(Debug, Clone)]
pub struct VectorMeshData {
    /// Vertex positions in world space `[x, y, z]` (f64 for precision).
    pub positions: Vec<[f64; 3]>,
    /// Per-vertex colour `[r, g, b, a]` (0--1 range, linear).
    pub colors: Vec<[f32; 4]>,
    /// Per-vertex surface normals `[nx, ny, nz]`.
    ///
    /// Empty for flat geometry (fills, lines, circles).  Populated for
    /// 3-D geometry such as fill-extrusions where per-face normals are
    /// needed for proper lighting.  When non-empty, the length **must**
    /// equal `positions.len()`.
    pub normals: Vec<[f32; 3]>,
    /// Triangle indices into `positions` / `colors` / `normals`.
    pub indices: Vec<u32>,
    /// High-level render family that produced this mesh.
    ///
    /// Renderers use this to select the appropriate GPU pipeline
    /// (e.g. lit fill-extrusion vs. flat fill).
    pub render_mode: VectorRenderMode,

    // -- Line-specific data -----------------------------------------------

    /// Per-vertex distance along the polyline centreline (meters in world
    /// space).  Non-empty only for `VectorRenderMode::Line`.  The GPU line
    /// shader uses this for dash-pattern evaluation.
    pub line_distances: Vec<f32>,
    /// Per-vertex extrusion normal `[nx, ny]` (unit-length direction
    /// perpendicular to the line centreline).  Non-empty only for
    /// `VectorRenderMode::Line`.
    pub line_normals: Vec<[f32; 2]>,
    /// Per-vertex cap/join flag.  `1.0` for round cap/join fan vertices,
    /// `0.0` for ribbon body and non-round cap/join vertices.  The GPU
    /// line shader uses this to switch between linear edge AA and
    /// SDF circle-based AA.  Non-empty only for `VectorRenderMode::Line`.
    pub line_cap_joins: Vec<f32>,
    /// Line style parameters `[dash_length, gap_length, half_width, cap_round]`.
    /// Uniform across all vertices in a single mesh.  `cap_round` is 1.0
    /// for round caps and 0.0 for butt caps.
    pub line_params: [f32; 4],

    // -- Circle-specific data ---------------------------------------------

    /// Per-instance circle data: `[center_x, center_y, center_z, radius]`
    /// in world space (f64 centre, f32 radius).
    pub circle_instances: Vec<CircleInstanceData>,

    // -- Heatmap-specific data --------------------------------------------

    /// Per-point heatmap data: `[x, y, weight, radius]` in world space.
    pub heatmap_points: Vec<[f64; 4]>,
    /// Heatmap intensity multiplier.
    pub heatmap_intensity: f32,

    // -- Fill-specific data -----------------------------------------------

    /// Fill-layer pixel translate offset `[tx, ty]`.
    pub fill_translate: [f32; 2],
    /// Fill-layer opacity (separate from vertex alpha).
    pub fill_opacity: f32,
    /// Whether fill edges should be antialiased.
    pub fill_antialias: bool,
    /// Outline colour override for fill outlines.
    /// When `[0,0,0,0]`, the outline uses the fill colour.
    pub fill_outline_color: [f32; 4],
    /// Optional pattern image for fill-pattern rendering.
    ///
    /// When present, the renderer creates a repeating texture and
    /// uses `fill_pattern_uvs` to sample it.  Non-empty only for
    /// `VectorRenderMode::Fill` with a pattern set.
    pub fill_pattern: Option<Arc<PatternImage>>,
    /// Per-vertex pattern UV coordinates `[u, v]`.
    ///
    /// Populated only when `fill_pattern` is `Some`.  The coordinates
    /// are in pattern-tile units: `(0,0)` is the pattern origin,
    /// `(1,1)` is one full pattern repetition.  Values outside `[0,1]`
    /// repeat via the GPU's `Repeat` address mode.
    pub fill_pattern_uvs: Vec<[f32; 2]>,

    // -- Line-pattern data ------------------------------------------------

    /// Optional pattern image for line-pattern rendering.
    ///
    /// When present, the renderer creates a repeating texture and
    /// uses `line_pattern_uvs` to sample it.  Non-empty only for
    /// `VectorRenderMode::Line` with a pattern set.
    pub line_pattern: Option<Arc<PatternImage>>,
    /// Per-vertex pattern UV coordinates `[u, v]` for line-pattern rendering.
    ///
    /// U maps along the line centreline (`distance / pattern_width`),
    /// V maps across the line width (`0.0` = left edge, `1.0` = right edge).
    /// Values outside `[0,1]` on the U axis repeat via the GPU's `Repeat`
    /// address mode.
    pub line_pattern_uvs: Vec<[f32; 2]>,
}

impl VectorMeshData {
    /// Whether the mesh contains no geometry.
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.indices.is_empty()
    }

    /// Number of vertices.
    #[inline]
    pub fn vertex_count(&self) -> usize {
        self.positions.len()
    }

    /// Number of triangle indices (always a multiple of 3 in valid meshes).
    #[inline]
    pub fn index_count(&self) -> usize {
        self.indices.len()
    }

    /// Number of triangles.
    #[inline]
    pub fn triangle_count(&self) -> usize {
        self.indices.len() / 3
    }

    /// Whether this mesh carries per-vertex normals for lighting.
    #[inline]
    pub fn has_normals(&self) -> bool {
        !self.normals.is_empty()
    }

    /// Append another mesh into this one, adjusting indices.
    pub fn merge(&mut self, other: &VectorMeshData) {
        let base = self.positions.len() as u32;
        self.positions.extend_from_slice(&other.positions);
        self.colors.extend_from_slice(&other.colors);
        self.normals.extend_from_slice(&other.normals);
        self.line_distances.extend_from_slice(&other.line_distances);
        self.line_normals.extend_from_slice(&other.line_normals);
        self.fill_pattern_uvs.extend_from_slice(&other.fill_pattern_uvs);
        self.line_pattern_uvs.extend_from_slice(&other.line_pattern_uvs);
        self.indices.extend(other.indices.iter().map(|i| base + i));
        self.circle_instances.extend_from_slice(&other.circle_instances);
        self.heatmap_points.extend_from_slice(&other.heatmap_points);
    }

    /// Remove all vertices and indices.
    pub fn clear(&mut self) {
        self.positions.clear();
        self.colors.clear();
        self.normals.clear();
        self.line_distances.clear();
        self.line_normals.clear();
        self.indices.clear();
        self.circle_instances.clear();
        self.heatmap_points.clear();
        self.fill_translate = [0.0, 0.0];
        self.fill_opacity = 1.0;
        self.fill_antialias = true;
        self.fill_outline_color = [0.0, 0.0, 0.0, 0.0];
        self.fill_pattern = None;
        self.fill_pattern_uvs.clear();
        self.line_pattern = None;
        self.line_pattern_uvs.clear();
    }
}

impl Default for VectorMeshData {
    fn default() -> Self {
        Self {
            positions: Vec::new(),
            colors: Vec::new(),
            normals: Vec::new(),
            indices: Vec::new(),
            render_mode: VectorRenderMode::Generic,
            line_distances: Vec::new(),
            line_normals: Vec::new(),
            line_cap_joins: Vec::new(),
            line_params: [0.0; 4],
            circle_instances: Vec::new(),
            heatmap_points: Vec::new(),
            heatmap_intensity: 0.0,
            fill_translate: [0.0, 0.0],
            fill_opacity: 1.0,
            fill_antialias: true,
            fill_outline_color: [0.0, 0.0, 0.0, 0.0],
            fill_pattern: None,
            fill_pattern_uvs: Vec::new(),
            line_pattern: None,
            line_pattern_uvs: Vec::new(),
        }
    }
}

// ---------------------------------------------------------------------------
// VectorLayer
// ---------------------------------------------------------------------------

/// A vector layer holding parsed geographic features with a render style.
///
/// See the [module-level documentation](self) for the tessellation
/// pipeline and coordinate flow.
pub struct VectorLayer {
    id: LayerId,
    name: String,
    visible: bool,
    opacity: f32,
    /// Optional originating style layer id for query APIs.
    pub query_layer_id: Option<String>,
    /// Optional originating style source id for query APIs.
    pub query_source_id: Option<String>,
    /// Optional originating style source-layer id for streamed vector sources.
    pub query_source_layer: Option<String>,
    /// The feature data.
    pub features: FeatureCollection,
    /// Per-feature tile/source-layer provenance.
    pub feature_provenance: Vec<Option<FeatureProvenance>>,
    /// Render style.
    pub style: VectorStyle,
    /// Monotonically increasing counter bumped whenever feature data changes
    /// via [`set_features_with_provenance`](Self::set_features_with_provenance).
    /// Used by the sync-path tessellation cache to detect data staleness.
    data_generation: u64,
}

impl std::fmt::Debug for VectorLayer {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("VectorLayer")
            .field("id", &self.id)
            .field("name", &self.name)
            .field("visible", &self.visible)
            .field("opacity", &self.opacity)
            .field("feature_count", &self.features.len())
            .field("style", &self.style)
            .finish()
    }
}

impl VectorLayer {
    /// Create a new vector layer.
    pub fn new(name: impl Into<String>, features: FeatureCollection, style: VectorStyle) -> Self {
        Self {
            id: LayerId::next(),
            name: name.into(),
            visible: true,
            opacity: 1.0,
            query_layer_id: None,
            query_source_id: None,
            query_source_layer: None,
            feature_provenance: vec![None; features.len()],
            features,
            style,
            data_generation: 0,
        }
    }

    /// Attach style/runtime query metadata to this layer.
    pub fn with_query_metadata(
        mut self,
        layer_id: impl Into<Option<String>>,
        source_id: impl Into<Option<String>>,
    ) -> Self {
        self.query_layer_id = layer_id.into();
        self.query_source_id = source_id.into();
        self
    }

    /// Attach the originating source-layer id used by style/runtime evaluation.
    pub fn with_source_layer(mut self, source_layer: Option<String>) -> Self {
        self.query_source_layer = source_layer;
        self
    }

    /// Replace the feature set together with per-feature provenance.
    pub fn set_features_with_provenance(
        &mut self,
        features: FeatureCollection,
        mut provenance: Vec<Option<FeatureProvenance>>,
    ) {
        if provenance.len() < features.len() {
            provenance.resize(features.len(), None);
        } else if provenance.len() > features.len() {
            provenance.truncate(features.len());
        }
        self.features = features;
        self.feature_provenance = provenance;
        self.data_generation = self.data_generation.wrapping_add(1);
    }

    /// Monotonically increasing generation counter for feature data changes.
    ///
    /// Bumped by [`set_features_with_provenance`](Self::set_features_with_provenance).
    /// Used by the sync-path tessellation cache to detect data staleness.
    #[inline]
    pub fn data_generation(&self) -> u64 {
        self.data_generation
    }

    /// Attach style/runtime query metadata to this layer in place.
    pub fn set_query_metadata(&mut self, layer_id: Option<String>, source_id: Option<String>) {
        self.query_layer_id = layer_id;
        self.query_source_id = source_id;
    }

    // -- Queries ----------------------------------------------------------

    /// Number of features in this layer.
    #[inline]
    pub fn feature_count(&self) -> usize {
        self.features.len()
    }

    /// Total number of coordinate vertices across all features.
    #[inline]
    pub fn total_coords(&self) -> usize {
        self.features.total_coords()
    }

    // -- Terrain draping --------------------------------------------------

    /// Drape all vector features onto terrain by querying elevation
    /// for each vertex and setting its altitude.
    ///
    /// Does nothing if terrain is disabled or elevation data is
    /// unavailable for a given coordinate (the vertex retains its
    /// original altitude).
    pub fn drape_on_terrain(&mut self, terrain: &TerrainManager) {
        if !terrain.enabled() {
            return;
        }
        for feature in &mut self.features.features {
            drape_geometry(&mut feature.geometry, terrain);
        }
    }

    // -- Tessellation -----------------------------------------------------

    /// Tessellate all features into GPU-ready mesh data.
    ///
    /// - **Polygons** are fan-triangulated (exterior ring only; holes
    ///   are not yet subtracted).
    /// - **Line strings** are stroke-expanded into ribbon quads with
    ///   the configured [`stroke_width`](VectorStyle::stroke_width).
    /// - **Points** are rendered as small axis-aligned quads.
    /// - **Multi\*** and **GeometryCollection** types recurse into
    ///   their children.
    ///
    /// When the style carries data-driven expressions for width or colour,
    /// those are evaluated per feature against each feature's properties.
    ///
    /// All output positions are in the active planar world-space meters.
    pub fn tessellate(&self, projection: CameraProjection) -> VectorMeshData {
        let mut mesh = VectorMeshData {
            render_mode: self.style.render_mode,
            ..VectorMeshData::default()
        };

        let dd_width = self.style.is_width_data_driven();
        let dd_color = self.style.is_stroke_color_data_driven();
        let default_half_width = self.style.stroke_width as f64 * DEGREES_PER_PIXEL_APPROX;

        if dd_width || dd_color {
            // Data-driven path: evaluate width/color per feature.
            for feature in &self.features.features {
                let half_width = if dd_width {
                    self.style.evaluate_width(feature) as f64 * DEGREES_PER_PIXEL_APPROX
                } else {
                    default_half_width
                };
                if dd_color {
                    let color = self.style.evaluate_stroke_color(feature);
                    let mut feature_style = self.style.clone();
                    feature_style.stroke_color = color;
                    tessellate_geometry(
                        &feature.geometry,
                        &feature_style,
                        projection,
                        half_width,
                        &mut mesh,
                    );
                } else {
                    tessellate_geometry(
                        &feature.geometry,
                        &self.style,
                        projection,
                        half_width,
                        &mut mesh,
                    );
                }
            }
        } else {
            // Fast path: uniform width and color for all features.
            for feature in &self.features.features {
                tessellate_geometry(
                    &feature.geometry,
                    &self.style,
                    projection,
                    default_half_width,
                    &mut mesh,
                );
            }
        }

        // Propagate fill-specific style parameters to the mesh data so the
        // renderer has access without needing the full VectorStyle.
        if self.style.render_mode == VectorRenderMode::Fill {
            mesh.fill_translate = self.style.fill_translate;
            mesh.fill_opacity = self.style.fill_opacity;
            mesh.fill_antialias = self.style.fill_antialias;
            mesh.fill_outline_color = self.style.fill_outline_color
                .unwrap_or(self.style.stroke_color);
        }

        // Propagate line-specific style parameters so the GPU line shader
        // can evaluate dash patterns and cap styles without the full style.
        if self.style.render_mode == VectorRenderMode::Line {
            let (dash_len, gap_len) = match &self.style.dash_array {
                Some(arr) if arr.len() >= 2 => (arr[0], arr[1]),
                _ => (0.0, 0.0),
            };
            let cap_round = match self.style.line_cap {
                LineCap::Round => 1.0,
                _ => 0.0,
            };
            mesh.line_params = [dash_len, gap_len, cap_round, 0.0];
        }

        mesh
    }

    /// Build symbol-placement candidates for this layer.
    pub fn symbol_candidates(&self) -> Vec<SymbolCandidate> {
        self.symbol_candidates_for_features(&self.features, &self.feature_provenance)
    }

    /// Build symbol-placement candidates from an explicit feature/provenance set.
    pub fn symbol_candidates_for_features(
        &self,
        features: &FeatureCollection,
        feature_provenance: &[Option<FeatureProvenance>],
    ) -> Vec<SymbolCandidate> {
        if self.style.render_mode != VectorRenderMode::Symbol {
            return Vec::new();
        }

        let mut out = Vec::new();
        for (feature_index, feature) in features.features.iter().enumerate() {
            collect_symbol_candidates_from_geometry(
                self.id,
                self.query_layer_id.as_deref(),
                self.query_source_id.as_deref(),
                feature_provenance.get(feature_index).and_then(|p| p.as_ref()),
                feature_index,
                0,
                feature,
                &feature.geometry,
                &self.style,
                &mut out,
            );
        }
        out
    }
}

fn collect_symbol_candidates_from_geometry(
    layer_id: LayerId,
    query_layer_id: Option<&str>,
    query_source_id: Option<&str>,
    provenance: Option<&FeatureProvenance>,
    feature_index: usize,
    point_index: usize,
    feature: &Feature,
    geometry: &Geometry,
    style: &VectorStyle,
    out: &mut Vec<SymbolCandidate>,
) -> usize {
    if style.symbol_placement == SymbolPlacement::Line {
        return collect_line_symbol_candidates_from_geometry(
            layer_id,
            query_layer_id,
            query_source_id,
            provenance,
            feature_index,
            point_index,
            feature,
            geometry,
            style,
            out,
        );
    }

    match geometry {
        Geometry::Point(point) => {
            let candidates = symbol_candidates_for_point(
                layer_id,
                query_layer_id,
                query_source_id,
                provenance,
                feature_index,
                point_index,
                feature,
                point.coord,
                style,
            );
            out.extend(candidates);
            point_index + 1
        }
        Geometry::MultiPoint(points) => {
            let mut next = point_index;
            for point in &points.points {
                next = collect_symbol_candidates_from_geometry(
                    layer_id,
                    query_layer_id,
                    query_source_id,
                    provenance,
                    feature_index,
                    next,
                    feature,
                    &Geometry::Point(point.clone()),
                    style,
                    out,
                );
            }
            next
        }
        Geometry::GeometryCollection(geometries) => {
            let mut next = point_index;
            for geometry in geometries {
                next = collect_symbol_candidates_from_geometry(
                    layer_id,
                    query_layer_id,
                    query_source_id,
                    provenance,
                    feature_index,
                    next,
                    feature,
                    geometry,
                    style,
                    out,
                );
            }
            next
        }
        _ => point_index,
    }
}

fn collect_line_symbol_candidates_from_geometry(
    layer_id: LayerId,
    query_layer_id: Option<&str>,
    query_source_id: Option<&str>,
    provenance: Option<&FeatureProvenance>,
    feature_index: usize,
    point_index: usize,
    feature: &Feature,
    geometry: &Geometry,
    style: &VectorStyle,
    out: &mut Vec<SymbolCandidate>,
) -> usize {
    match geometry {
        Geometry::LineString(line) => {
            let mut next = point_index;
            let label_length = estimated_line_label_length_meters(feature, style);
            for (slot_index, anchor) in line_placement_anchors(line, style, label_length).into_iter().enumerate() {
                let candidates = symbol_candidates_at_anchor(
                    layer_id,
                    query_layer_id,
                    query_source_id,
                    provenance,
                    feature_index,
                    next,
                    feature,
                    anchor.coord,
                    style,
                    anchor.rotation_rad,
                    Some(slot_index),
                );
                next += candidates.len();
                out.extend(candidates);
            }
            next
        }
        Geometry::MultiLineString(lines) => {
            let mut next = point_index;
            for line in &lines.lines {
                next = collect_line_symbol_candidates_from_geometry(
                    layer_id,
                    query_layer_id,
                    query_source_id,
                    provenance,
                    feature_index,
                    next,
                    feature,
                    &Geometry::LineString(line.clone()),
                    style,
                    out,
                );
            }
            next
        }
        Geometry::GeometryCollection(geometries) => {
            let mut next = point_index;
            for geometry in geometries {
                next = collect_line_symbol_candidates_from_geometry(
                    layer_id,
                    query_layer_id,
                    query_source_id,
                    provenance,
                    feature_index,
                    next,
                    feature,
                    geometry,
                    style,
                    out,
                );
            }
            next
        }
        _ => point_index,
    }
}

fn symbol_candidates_for_point(
    layer_id: LayerId,
    query_layer_id: Option<&str>,
    query_source_id: Option<&str>,
    provenance: Option<&FeatureProvenance>,
    feature_index: usize,
    point_index: usize,
    feature: &Feature,
    anchor: GeoCoord,
    style: &VectorStyle,
) -> Vec<SymbolCandidate> {
    symbol_candidates_at_anchor(
        layer_id,
        query_layer_id,
        query_source_id,
        provenance,
        feature_index,
        point_index,
        feature,
        anchor,
        style,
        0.0,
        None,
    )
}

fn symbol_candidates_at_anchor(
    layer_id: LayerId,
    query_layer_id: Option<&str>,
    query_source_id: Option<&str>,
    provenance: Option<&FeatureProvenance>,
    feature_index: usize,
    point_index: usize,
    feature: &Feature,
    anchor: GeoCoord,
    style: &VectorStyle,
    rotation_rad: f32,
    line_slot_index: Option<usize>,
) -> Vec<SymbolCandidate> {
    let feature_id = feature_id_for_feature(feature, feature_index);
    let text = style
        .symbol_text_field
        .as_deref()
        .and_then(|field| feature.property(field))
        .and_then(symbol_text_from_property)
        .map(|text| transform_symbol_text(text, style.symbol_text_transform));
    let icon_image = style.symbol_icon_image.clone();

    if text.is_none() && icon_image.is_none() {
        return Vec::new();
    }

/// Apply style-driven text transformation before measurement and placement.
///
/// Mapbox and MapLibre transform text before shaping, which means the rendered
/// label content and its measured footprint both use the transformed string.
/// The engine mirrors that ordering here so uppercase and lowercase styles
/// affect candidate text, wrapping, and collision estimates consistently.
fn transform_symbol_text(text: String, transform: SymbolTextTransform) -> String {
    match transform {
        SymbolTextTransform::None => text,
        SymbolTextTransform::Uppercase => text.to_uppercase(),
        SymbolTextTransform::Lowercase => text.to_lowercase(),
    }
}

    let cross_tile_id = symbol_cross_tile_id(
        query_layer_id,
        query_source_id,
        &feature_id,
        text.as_deref(),
        icon_image.as_deref(),
        anchor,
        style.symbol_placement,
        line_slot_index,
        style,
    );

    let base_id = format!("{}:{feature_index}:{point_index}", layer_id.as_u64());
    let text_present = text.is_some();
    let icon_present = icon_image.is_some();
    let text_optional = style.symbol_text_optional;
    let icon_optional = style.symbol_icon_optional;

    let mut variants = Vec::new();
    let base_candidate = make_symbol_candidate(
        &base_id,
        &base_id,
        query_layer_id,
        query_source_id,
        provenance,
        &feature_id,
        feature_index,
        style.symbol_placement,
        anchor,
        text.clone(),
        icon_image.clone(),
        style,
        cross_tile_id.clone(),
        rotation_rad,
    );
    variants.push(base_candidate);

    // The engine still renders text and icon together by default, but optional
    // flags need a way to keep one part visible when the full pair does not fit.
    // Emit fallback candidates with the same cross-tile identity so placement
    // can try the full pair first and then fall back to the optional subset.
    if text_present && icon_present {
        if text_optional {
            variants.push(make_symbol_candidate(
                &format!("{base_id}:icon-only"),
                &base_id,
                query_layer_id,
                query_source_id,
                provenance,
                &feature_id,
                feature_index,
                style.symbol_placement,
                anchor,
                None,
                icon_image.clone(),
                style,
                cross_tile_id.clone(),
                rotation_rad,
            ));
        }
        if icon_optional {
            variants.push(make_symbol_candidate(
                &format!("{base_id}:text-only"),
                &base_id,
                query_layer_id,
                query_source_id,
                provenance,
                &feature_id,
                feature_index,
                style.symbol_placement,
                anchor,
                text,
                None,
                style,
                cross_tile_id,
                rotation_rad,
            ));
        }
    }

    variants
}

fn make_symbol_candidate(
    id: &str,
    placement_group_id: &str,
    query_layer_id: Option<&str>,
    query_source_id: Option<&str>,
    provenance: Option<&FeatureProvenance>,
    feature_id: &str,
    feature_index: usize,
    placement: SymbolPlacement,
    anchor: GeoCoord,
    text: Option<String>,
    icon_image: Option<String>,
    style: &VectorStyle,
    cross_tile_id: String,
    rotation_rad: f32,
) -> SymbolCandidate {
    let has_text = text.is_some();
    let has_icon = icon_image.is_some();

    SymbolCandidate {
        id: id.to_owned(),
        layer_id: query_layer_id.map(ToOwned::to_owned),
        source_id: query_source_id.map(ToOwned::to_owned),
        source_layer: provenance.and_then(|p| p.source_layer.clone()),
        source_tile: provenance.and_then(|p| p.source_tile),
        feature_id: feature_id.to_owned(),
        feature_index,
        placement_group_id: placement_group_id.to_owned(),
        placement,
        anchor,
        text,
        icon_image,
        font_stack: style.symbol_font_stack.clone(),
        cross_tile_id,
        rotation_rad,
        size_px: style.symbol_size,
        padding_px: style.symbol_padding,
        allow_overlap: effective_symbol_overlap(style, has_text, has_icon),
        ignore_placement: effective_symbol_ignore_placement(style, has_text, has_icon),
        sort_key: style.symbol_sort_key,
        radial_offset: style.symbol_text_radial_offset,
        variable_anchor_offsets: style.symbol_variable_anchor_offsets.clone(),
        text_max_width: style.symbol_text_max_width,
        text_line_height: style.symbol_text_line_height,
        text_letter_spacing: style.symbol_text_letter_spacing,
        icon_text_fit: style.symbol_icon_text_fit,
        icon_text_fit_padding: style.symbol_icon_text_fit_padding,
        anchors: if style.symbol_variable_anchor_offsets.is_some() {
            style
                .symbol_variable_anchor_offsets
                .as_ref()
                .map(|offsets| offsets.iter().map(|(anchor, _)| *anchor).collect())
                .unwrap_or_default()
        } else {
            style.symbol_anchors.clone()
        },
        writing_mode: style.symbol_writing_mode,
        offset_px: style.symbol_offset,
        fill_color: style.fill_color,
        halo_color: style.symbol_halo_color,
    }
}

/// Resolve the simplified engine ignore-placement decision for a combined symbol.
///
/// Mapbox and MapLibre apply ignore-placement separately to text and icon
/// collision geometry. The engine still places a combined symbol candidate, so
/// it uses the same presence-based reduction as overlap handling: text-only and
/// icon-only fallbacks use their own flags, while a paired text+icon symbol
/// only skips blocking later symbols when both parts are configured to ignore
/// placement.
fn effective_symbol_ignore_placement(style: &VectorStyle, has_text: bool, has_icon: bool) -> bool {
    match (has_text, has_icon) {
        (true, true) => {
            style.symbol_text_ignore_placement && style.symbol_icon_ignore_placement
        }
        (true, false) => style.symbol_text_ignore_placement,
        (false, true) => style.symbol_icon_ignore_placement,
        (false, false) => false,
    }
}

/// Resolve the simplified engine overlap decision for a combined text/icon symbol.
///
/// Mapbox and MapLibre place text and icon collision data separately. The
/// engine still places them as one combined symbol candidate, so it uses the
/// narrowest overlap rule that is consistent with the parts that are actually
/// present: text-only symbols follow the text flag, icon-only symbols follow
/// the icon flag, and paired text+icon symbols may overlap only when both
/// parts are configured to allow overlap.
fn effective_symbol_overlap(style: &VectorStyle, has_text: bool, has_icon: bool) -> bool {
    match (has_text, has_icon) {
        (true, true) => style.symbol_text_allow_overlap && style.symbol_icon_allow_overlap,
        (true, false) => style.symbol_text_allow_overlap,
        (false, true) => style.symbol_icon_allow_overlap,
        (false, false) => style.symbol_allow_overlap,
    }
}

/// Build a placement identity that survives the kinds of updates expected for
/// the current symbol mode.
///
/// Point labels still use coordinate-based identities because their visual
/// anchor is the point itself. Line labels are different: repeated anchors can
/// move slightly when geometry or clipping changes, and neighboring tiles may
/// expose overlapping slices of the same underlying feature. To reduce visible
/// churn, line labels use a quantized world-anchor bucket keyed by feature id
/// and source/layer identity instead of a raw local slot index. That keeps
/// nearby anchors stable across small shifts while still distinguishing labels
/// that land in meaningfully different positions along the line.
fn symbol_cross_tile_id(
    query_layer_id: Option<&str>,
    query_source_id: Option<&str>,
    feature_id: &str,
    text: Option<&str>,
    icon_image: Option<&str>,
    anchor: GeoCoord,
    placement: SymbolPlacement,
    line_slot_index: Option<usize>,
    style: &VectorStyle,
) -> String {
    match placement {
        SymbolPlacement::Point => format!(
            "{}|{}|{:.6}|{:.6}",
            text.unwrap_or(""),
            icon_image.unwrap_or(""),
            anchor.lat,
            anchor.lon,
        ),
        SymbolPlacement::Line => {
            let slot = line_slot_index.unwrap_or(0);
            let world = CameraProjection::WebMercator.project(&anchor);
            // Use a coarse positional bucket alongside the slot index so that
            // genuinely different line windows produce different IDs while
            // small geometry shifts stay in the same bucket.  The bucket is
            // twice the spacing to absorb interpolation jitter from small
            // anchor shifts (~22m) while still distinguishing window shifts
            // on the order of a full spacing interval (~1113m).
            let coarse_bucket = ((style.symbol_spacing.max(style.symbol_size).max(1.0) as f64)
                * METERS_PER_PIXEL_APPROX
                * 2.0)
                .max(1.0);
            let bucket_x = (world.position.x / coarse_bucket).round() as i64;
            let bucket_y = (world.position.y / coarse_bucket).round() as i64;
            format!(
                "line|{}|{}|{}|{}|{}|{}|{}|{}",
                query_source_id.unwrap_or(""),
                query_layer_id.unwrap_or(""),
                feature_id,
                slot,
                bucket_x,
                bucket_y,
                text.unwrap_or(""),
                icon_image.unwrap_or(""),
            )
        }
    }
}

/// Choose repeated anchors for a line-placed label.
///
/// This is still a simplified version of Mapbox and MapLibre line placement:
/// we generate stable anchors along the path at approximately the requested
/// spacing and filter out anchors on sharp bends using a simplified
/// readability check. The retained anchor list is enough to move from one
/// midpoint label toward repeated line labels with stable ordering while full
/// path-shaped glyph layout remains future work.
fn line_placement_anchors(
    line: &crate::geometry::LineString,
    style: &VectorStyle,
    label_length: f64,
) -> Vec<LinePlacementAnchor> {
    if line.coords.len() < 2 {
        return Vec::new();
    }

    let projected: Vec<_> = line
        .coords
        .iter()
        .map(|coord| CameraProjection::WebMercator.project(coord))
        .collect();
    let total_length: f64 = projected
        .windows(2)
        .map(|segment| {
            let a = segment[0].position;
            let b = segment[1].position;
            let dx = b.x - a.x;
            let dy = b.y - a.y;
            let dz = b.z - a.z;
            (dx * dx + dy * dy + dz * dz).sqrt()
        })
        .sum();
    if total_length <= f64::EPSILON {
        return line
            .coords
            .first()
            .copied()
            .map(|coord| LinePlacementAnchor {
                coord,
                rotation_rad: 0.0,
                distance: total_length * 0.5,
            })
            .into_iter()
            .collect();
    }

    // Full style-spec parity would derive spacing in tile units after symbol
    // shaping. Until that layout stage exists in the engine, use the same
    // approximate pixel-to-world conversion already used elsewhere in the
    // vector layer so repeated line anchors stay stable and configurable.
    let spacing = (style.symbol_spacing.max(style.symbol_size).max(1.0) as f64)
        * METERS_PER_PIXEL_APPROX;
    if spacing <= f64::EPSILON || total_length <= spacing {
        return interpolate_line_anchor_at_distance(
            line,
            &projected,
            total_length * 0.5,
            style.symbol_keep_upright,
        )
            .filter(|anchor| line_anchor_passes_max_angle(&projected, anchor.distance, label_length, style))
            .into_iter()
            .collect();
    }

    let mut anchors = Vec::new();
    let mut target = spacing * 0.5;
    while target < total_length {
        if let Some(anchor) =
            interpolate_line_anchor_at_distance(line, &projected, target, style.symbol_keep_upright)
        {
            if line_anchor_passes_max_angle(&projected, anchor.distance, label_length, style) {
                anchors.push(anchor);
            }
        }
        target += spacing;
    }

    if anchors.is_empty() {
        interpolate_line_anchor_at_distance(
            line,
            &projected,
            total_length * 0.5,
            style.symbol_keep_upright,
        )
            .filter(|anchor| line_anchor_passes_max_angle(&projected, anchor.distance, label_length, style))
            .into_iter()
            .collect()
    } else {
        anchors
    }
}

/// Estimate the on-line footprint of a label in world meters.
///
/// The engine does not yet run full text shaping during candidate generation,
/// so this uses the same lightweight text/icon size heuristic as the placeholder
/// symbol mesh. That keeps line-anchor spacing and angle filtering consistent
/// with the current symbol collision approximation.
fn estimated_line_label_length_meters(feature: &Feature, style: &VectorStyle) -> f64 {
    let text = style
        .symbol_text_field
        .as_deref()
        .and_then(|field| feature.property(field))
        .and_then(symbol_text_from_property);
    let icon = style.symbol_icon_image.as_deref();
    let size_px = style.symbol_size.max(1.0) as f64;
    let text_width_px = text
        .as_deref()
        .map(|value| value.chars().count() as f64 * size_px * 0.6)
        .unwrap_or(0.0);
    let icon_width_px = if icon.is_some() { size_px * 1.2 } else { 0.0 };
    (text_width_px.max(size_px) + icon_width_px + style.symbol_padding.max(0.0) as f64 * 2.0)
        * METERS_PER_PIXEL_APPROX
}

/// Reject line anchors whose surrounding path bends too sharply.
///
/// Mapbox and MapLibre use a sliding angle window tied to shaped label length.
/// The engine keeps this simpler for now by summing turn angles across the
/// retained label span around each anchor. That still removes the least
/// readable anchors while keeping the implementation small and predictable.
fn line_anchor_passes_max_angle(
    projected: &[WorldCoord],
    anchor_distance: f64,
    label_length: f64,
    style: &VectorStyle,
) -> bool {
    if projected.len() < 3 {
        return true;
    }
    let half_label = label_length * 0.5;
    if anchor_distance - half_label < 0.0 || anchor_distance + half_label > line_total_length(projected) {
        return false;
    }

    let max_angle = style.symbol_max_angle.max(0.0) as f64 * std::f64::consts::PI / 180.0;
    if max_angle >= std::f64::consts::PI {
        return true;
    }

    let start = anchor_distance - half_label;
    let end = anchor_distance + half_label;
    let mut distance = 0.0;
    let mut accumulated_turn = 0.0;

    for index in 1..projected.len() - 1 {
        let prev = projected[index - 1].position;
        let current = projected[index].position;
        let next = projected[index + 1].position;
        let segment_dx = current.x - prev.x;
        let segment_dy = current.y - prev.y;
        let segment_dz = current.z - prev.z;
        distance += (segment_dx * segment_dx + segment_dy * segment_dy + segment_dz * segment_dz).sqrt();
        if distance < start || distance > end {
            continue;
        }

        let prev_angle = (current.y - prev.y).atan2(current.x - prev.x);
        let next_angle = (next.y - current.y).atan2(next.x - current.x);
        accumulated_turn += normalize_angle_delta(next_angle - prev_angle).abs();
        if accumulated_turn > max_angle {
            return false;
        }
    }

    true
}

fn normalize_angle_delta(angle: f64) -> f64 {
    ((angle + std::f64::consts::PI * 3.0) % (std::f64::consts::PI * 2.0))
        - std::f64::consts::PI
}

fn line_total_length(projected: &[WorldCoord]) -> f64 {
    projected
        .windows(2)
        .map(|segment| {
            let a = segment[0].position;
            let b = segment[1].position;
            let dx = b.x - a.x;
            let dy = b.y - a.y;
            let dz = b.z - a.z;
            (dx * dx + dy * dy + dz * dz).sqrt()
        })
        .sum()
}

fn interpolate_line_anchor_at_distance(
    line: &crate::geometry::LineString,
    projected: &[WorldCoord],
    target: f64,
    keep_upright: bool,
) -> Option<LinePlacementAnchor> {
    let mut traversed = 0.0;
    for (coords, segment) in line.coords.windows(2).zip(projected.windows(2)) {
        let a = segment[0].position;
        let b = segment[1].position;
        let dx = b.x - a.x;
        let dy = b.y - a.y;
        let dz = b.z - a.z;
        let segment_length = (dx * dx + dy * dy + dz * dz).sqrt();
        if segment_length <= f64::EPSILON {
            continue;
        }
        if traversed + segment_length >= target {
            let t = ((target - traversed) / segment_length).clamp(0.0, 1.0);
            let start = coords[0];
            let end = coords[1];
            let coord = GeoCoord::new(
                start.lat + (end.lat - start.lat) * t,
                start.lon + (end.lon - start.lon) * t,
                start.alt + (end.alt - start.alt) * t,
            );
            // Use the projected segment direction so placeholder symbol quads
            // rotate with the rendered path in the active working projection.
            let rotation_rad = normalize_line_label_rotation(
                (b.y - a.y).atan2(b.x - a.x) as f32,
                keep_upright,
            );
            return Some(LinePlacementAnchor {
                coord,
                rotation_rad,
                distance: target,
            });
        }
        traversed += segment_length;
    }

    line.coords.last().copied().map(|coord| LinePlacementAnchor {
        coord,
        rotation_rad: 0.0,
        distance: target,
    })
}

/// Normalize a line-label rotation into an upright range.
///
/// With `text-keep-upright`, Mapbox and MapLibre avoid rendering line labels
/// upside down by flipping them 180 degrees when the local line direction
/// would otherwise exceed the readable range. The engine mirrors that intent
/// with a small normalization step over the already-computed line angle.
fn normalize_line_label_rotation(rotation_rad: f32, keep_upright: bool) -> f32 {
    if !keep_upright {
        return rotation_rad;
    }

    let mut normalized = rotation_rad;
    while normalized > std::f32::consts::PI {
        normalized -= std::f32::consts::TAU;
    }
    while normalized < -std::f32::consts::PI {
        normalized += std::f32::consts::TAU;
    }
    if normalized > std::f32::consts::FRAC_PI_2 {
        normalized -= std::f32::consts::PI;
    } else if normalized < -std::f32::consts::FRAC_PI_2 {
        normalized += std::f32::consts::PI;
    }
    normalized
}

fn symbol_text_from_property(value: &crate::geometry::PropertyValue) -> Option<String> {
    match value {
        crate::geometry::PropertyValue::Null => None,
        crate::geometry::PropertyValue::Bool(value) => Some(value.to_string()),
        crate::geometry::PropertyValue::Number(value) => Some(value.to_string()),
        crate::geometry::PropertyValue::String(value) => Some(value.clone()),
    }
}

// ---------------------------------------------------------------------------
// Tessellation (module-private)
// ---------------------------------------------------------------------------

/// Recursively tessellate a geometry into `mesh`.
///
/// Multi\* and GeometryCollection variants delegate to their children
/// **by reference** to avoid cloning geometry data.
fn tessellate_geometry(
    geometry: &Geometry,
    style: &VectorStyle,
    projection: CameraProjection,
    half_width: f64,
    mesh: &mut VectorMeshData,
) {
    match style.render_mode {
        VectorRenderMode::Generic => tessellate_generic_geometry(geometry, style, projection, half_width, mesh),
        VectorRenderMode::Fill => tessellate_fill_geometry(geometry, style, projection, mesh),
        VectorRenderMode::Line => tessellate_line_geometry(geometry, style, projection, half_width, mesh),
        VectorRenderMode::Circle => tessellate_circle_geometry(geometry, style, projection, mesh),
        VectorRenderMode::Heatmap => tessellate_heatmap_geometry(geometry, style, projection, mesh),
        VectorRenderMode::FillExtrusion => tessellate_fill_extrusion_geometry(geometry, style, projection, mesh),
        VectorRenderMode::Symbol => tessellate_symbol_geometry(geometry, style, projection, mesh),
    }
}

fn tessellate_generic_geometry(
    geometry: &Geometry,
    style: &VectorStyle,
    projection: CameraProjection,
    half_width: f64,
    mesh: &mut VectorMeshData,
) {
    match geometry {
        Geometry::Point(p) => append_square_marker(mesh, &p.coord, projection, half_width * METERS_PER_DEGREE, style.fill_color),
        Geometry::LineString(ls) => append_stroked_line(mesh, &ls.coords, projection, half_width, style.stroke_color, style),
        Geometry::Polygon(poly) => append_polygon_fill(mesh, &poly.exterior, projection, style.fill_color, None),
        Geometry::MultiPoint(mp) => {
            for p in &mp.points {
                tessellate_generic_geometry(&Geometry::Point(p.clone()), style, projection, half_width, mesh);
            }
        }
        Geometry::MultiLineString(mls) => {
            for ls in &mls.lines {
                tessellate_generic_geometry(&Geometry::LineString(ls.clone()), style, projection, half_width, mesh);
            }
        }
        Geometry::MultiPolygon(mpoly) => {
            for poly in &mpoly.polygons {
                tessellate_generic_geometry(&Geometry::Polygon(poly.clone()), style, projection, half_width, mesh);
            }
        }
        Geometry::GeometryCollection(geoms) => {
            for g in geoms {
                tessellate_generic_geometry(g, style, projection, half_width, mesh);
            }
        }
    }
}

fn tessellate_fill_geometry(geometry: &Geometry, style: &VectorStyle, projection: CameraProjection, mesh: &mut VectorMeshData) {
    // Carry the pattern image to the mesh so the renderer can access it.
    if style.fill_pattern.is_some() && mesh.fill_pattern.is_none() {
        mesh.fill_pattern = style.fill_pattern.clone();
    }

    match geometry {
        Geometry::Polygon(poly) => {
            append_polygon_fill(mesh, &poly.exterior, projection, style.fill_color, style.fill_pattern.as_deref());
            if style.stroke_width > 0.0 {
                append_stroked_line(mesh, &poly.exterior, projection, style.stroke_width as f64 * DEGREES_PER_PIXEL_APPROX, style.stroke_color, style);
                for hole in &poly.interiors {
                    append_stroked_line(mesh, hole, projection, style.stroke_width as f64 * DEGREES_PER_PIXEL_APPROX, style.stroke_color, style);
                }
            }
        }
        Geometry::MultiPolygon(mpoly) => {
            for poly in &mpoly.polygons {
                tessellate_fill_geometry(&Geometry::Polygon(poly.clone()), style, projection, mesh);
            }
        }
        Geometry::GeometryCollection(geoms) => {
            for g in geoms {
                tessellate_fill_geometry(g, style, projection, mesh);
            }
        }
        _ => {}
    }
}

fn tessellate_line_geometry(
    geometry: &Geometry,
    style: &VectorStyle,
    projection: CameraProjection,
    half_width: f64,
    mesh: &mut VectorMeshData,
) {
    // Carry the pattern image to the mesh so the renderer can access it.
    if style.line_pattern.is_some() && mesh.line_pattern.is_none() {
        mesh.line_pattern = style.line_pattern.clone();
    }

    match geometry {
        Geometry::LineString(ls) => append_stroked_line(mesh, &ls.coords, projection, half_width, style.stroke_color, style),
        Geometry::Polygon(poly) => {
            append_stroked_line(mesh, &poly.exterior, projection, half_width, style.stroke_color, style);
            for hole in &poly.interiors {
                append_stroked_line(mesh, hole, projection, half_width, style.stroke_color, style);
            }
        }
        Geometry::MultiLineString(mls) => {
            for ls in &mls.lines {
                tessellate_line_geometry(&Geometry::LineString(ls.clone()), style, projection, half_width, mesh);
            }
        }
        Geometry::MultiPolygon(mpoly) => {
            for poly in &mpoly.polygons {
                tessellate_line_geometry(&Geometry::Polygon(poly.clone()), style, projection, half_width, mesh);
            }
        }
        Geometry::GeometryCollection(geoms) => {
            for g in geoms {
                tessellate_line_geometry(g, style, projection, half_width, mesh);
            }
        }
        _ => {}
    }
}

fn tessellate_circle_geometry(geometry: &Geometry, style: &VectorStyle, projection: CameraProjection, mesh: &mut VectorMeshData) {
    match geometry {
        Geometry::Point(p) => {
            let radius = style.point_radius as f64 * DEGREES_PER_PIXEL_APPROX * METERS_PER_DEGREE;
            let stroke_w = style.stroke_width.max(0.0) as f64 * DEGREES_PER_PIXEL_APPROX * METERS_PER_DEGREE;
            append_circle(mesh, &p.coord, projection, radius, style.fill_color, Some((style.stroke_color, stroke_w)));

            // Also populate the instanced circle data used by the WGPU
            // SDF circle pipeline (screen-aligned quads evaluated by the
            // fragment shader).
            let w = projection.project(&p.coord);
            mesh.circle_instances.push(CircleInstanceData {
                center: [w.position.x, w.position.y, w.position.z],
                radius: radius as f32,
                color: style.fill_color,
                stroke_color: style.stroke_color,
                stroke_width: stroke_w as f32,
                blur: 0.0,
            });
        }
        Geometry::MultiPoint(mp) => {
            for p in &mp.points {
                tessellate_circle_geometry(&Geometry::Point(p.clone()), style, projection, mesh);
            }
        }
        Geometry::GeometryCollection(geoms) => {
            for g in geoms {
                tessellate_circle_geometry(g, style, projection, mesh);
            }
        }
        _ => {}
    }
}

fn tessellate_heatmap_geometry(geometry: &Geometry, style: &VectorStyle, projection: CameraProjection, mesh: &mut VectorMeshData) {
    match geometry {
        Geometry::Point(p) => {
            let radius = style.heatmap_radius.max(0.0) as f64 * DEGREES_PER_PIXEL_APPROX * METERS_PER_DEGREE;
            append_heat_blob(mesh, &p.coord, projection, radius, style.fill_color, style.heatmap_intensity.max(0.0));

            // Also populate the instanced heatmap data used by the WGPU
            // two-pass heatmap pipeline (accumulation + colormap).
            let w = projection.project(&p.coord);
            let weight = style.heatmap_intensity.max(0.0) as f64;
            mesh.heatmap_points.push([w.position.x, w.position.y, weight, radius]);
        }
        Geometry::MultiPoint(mp) => {
            for p in &mp.points {
                tessellate_heatmap_geometry(&Geometry::Point(p.clone()), style, projection, mesh);
            }
        }
        Geometry::GeometryCollection(geoms) => {
            for g in geoms {
                tessellate_heatmap_geometry(g, style, projection, mesh);
            }
        }
        _ => {}
    }
}

fn tessellate_fill_extrusion_geometry(geometry: &Geometry, style: &VectorStyle, projection: CameraProjection, mesh: &mut VectorMeshData) {
    match geometry {
        Geometry::Polygon(poly) => append_extruded_polygon(mesh, &poly.exterior, projection, style),
        Geometry::MultiPolygon(mpoly) => {
            for poly in &mpoly.polygons {
                append_extruded_polygon(mesh, &poly.exterior, projection, style);
            }
        }
        Geometry::GeometryCollection(geoms) => {
            for g in geoms {
                tessellate_fill_extrusion_geometry(g, style, projection, mesh);
            }
        }
        _ => {}
    }
}

fn tessellate_symbol_geometry(geometry: &Geometry, style: &VectorStyle, projection: CameraProjection, mesh: &mut VectorMeshData) {
    match geometry {
        Geometry::Point(p) => {
            let size = style.symbol_size.max(0.0) as f64 * DEGREES_PER_PIXEL_APPROX * METERS_PER_DEGREE;
            append_square_marker(mesh, &p.coord, projection, size * 1.35, style.symbol_halo_color);
            append_square_marker(mesh, &p.coord, projection, size, style.fill_color);
        }
        Geometry::MultiPoint(mp) => {
            for p in &mp.points {
                tessellate_symbol_geometry(&Geometry::Point(p.clone()), style, projection, mesh);
            }
        }
        Geometry::GeometryCollection(geoms) => {
            for g in geoms {
                tessellate_symbol_geometry(g, style, projection, mesh);
            }
        }
        _ => {}
    }
}

fn append_polygon_fill(mesh: &mut VectorMeshData, coords: &[GeoCoord], projection: CameraProjection, color: [f32; 4], pattern: Option<&PatternImage>) {
    let ring = normalized_ring(coords);
    if ring.len() < 3 {
        return;
    }
    let indices = tessellator::triangulate_polygon(&ring);
    let base = mesh.positions.len() as u32;
    for coord in &ring {
        let w = projection.project(coord);
        mesh.positions.push([w.position.x, w.position.y, w.position.z]);
        mesh.colors.push(color);

        // Generate pattern UVs when a fill-pattern is present.
        // One pattern repetition = pattern dimensions in meters.
        // World-space position is already in meters, so UV = pos / size.
        if let Some(pat) = pattern {
            let u = w.position.x as f32 / pat.width.max(1) as f32;
            let v = w.position.y as f32 / pat.height.max(1) as f32;
            mesh.fill_pattern_uvs.push([u, v]);
        }
    }
    for idx in indices {
        mesh.indices.push(base + idx);
    }
}

fn append_stroked_line(mesh: &mut VectorMeshData, coords: &[GeoCoord], projection: CameraProjection, half_width: f64, color: [f32; 4], style: &VectorStyle) {
    let result = tessellator::stroke_line_styled(
        coords,
        half_width,
        style.line_cap,
        style.line_join,
        style.miter_limit,
    );
    if result.positions.is_empty() {
        return;
    }

    // Pre-compute normalized distances for gradient evaluation.
    let gradient_max_dist = if style.line_gradient.is_some() {
        result
            .distances
            .iter()
            .cloned()
            .fold(0.0_f64, f64::max)
            .max(f64::EPSILON)
    } else {
        1.0
    };

    // Track left/right side alternation for line-pattern V coordinate.
    // Body vertices (cap_join = 0) are always pushed in left-right pairs
    // by the tessellator: left = 0.0, right = 1.0.
    // Cap/join fan vertices (cap_join = 1) get V = 0.5.
    let has_pattern = style.line_pattern.is_some();
    let pat_width = style.line_pattern.as_ref().map_or(1.0_f32, |p| p.width.max(1) as f32);
    let mut body_side = false; // false = left (V=0), true = right (V=1)

    let base = mesh.positions.len() as u32;
    for (i, pos) in result.positions.iter().enumerate() {
        let coord = GeoCoord::from_lat_lon(pos[1], pos[0]);
        let w = projection.project(&coord);
        mesh.positions.push([w.position.x, w.position.y, w.position.z]);

        // When a gradient is present, override the vertex colour with
        // the ramp evaluated at the normalised distance along the line.
        let vertex_color = if let Some(ref ramp) = style.line_gradient {
            let t = (result.distances[i] / gradient_max_dist) as f32;
            ramp.evaluate(t)
        } else {
            color
        };
        mesh.colors.push(vertex_color);

        mesh.line_normals.push([result.normals[i][0] as f32, result.normals[i][1] as f32]);
        // Convert distance from degrees to approximate meters for the shader.
        let dist_meters = (result.distances[i] * METERS_PER_DEGREE) as f32;
        mesh.line_distances.push(dist_meters);
        mesh.line_cap_joins.push(result.cap_join[i]);

        // Generate line-pattern UVs when a pattern is present.
        // U = distance_meters / pattern_width (repeats via GPU sampler).
        // V = perpendicular position across line width [0 = left, 1 = right].
        if has_pattern {
            let u = dist_meters / pat_width;
            let v = if result.cap_join[i] > 0.5 {
                // Cap/join fan vertex — map to centre.
                0.5
            } else {
                // Body vertex — alternate left (0) / right (1).
                let v = if body_side { 1.0 } else { 0.0 };
                body_side = !body_side;
                v
            };
            mesh.line_pattern_uvs.push([u, v]);
        }
    }
    for idx in &result.indices {
        mesh.indices.push(base + idx);
    }
}

fn append_square_marker(mesh: &mut VectorMeshData, coord: &GeoCoord, projection: CameraProjection, half_size: f64, color: [f32; 4]) {
    let w = projection.project(coord);
    let base = mesh.positions.len() as u32;
    mesh.positions.push([w.position.x - half_size, w.position.y - half_size, w.position.z]);
    mesh.positions.push([w.position.x + half_size, w.position.y - half_size, w.position.z]);
    mesh.positions.push([w.position.x + half_size, w.position.y + half_size, w.position.z]);
    mesh.positions.push([w.position.x - half_size, w.position.y + half_size, w.position.z]);
    for _ in 0..4 {
        mesh.colors.push(color);
    }
    mesh.indices.extend_from_slice(&[base, base + 1, base + 2, base, base + 2, base + 3]);
}

fn append_circle(
    mesh: &mut VectorMeshData,
    coord: &GeoCoord,
    projection: CameraProjection,
    radius: f64,
    fill_color: [f32; 4],
    outline: Option<([f32; 4], f64)>,
) {
    append_radial_fan(mesh, coord, projection, radius, fill_color, fill_color);
    if let Some((outline_color, outline_width)) = outline {
        if outline_width > 0.0 {
            let outer = radius + outline_width;
            append_ring(mesh, coord, projection, radius, outer, outline_color);
        }
    }
}

fn append_heat_blob(
    mesh: &mut VectorMeshData,
    coord: &GeoCoord,
    projection: CameraProjection,
    radius: f64,
    color: [f32; 4],
    intensity: f32,
) {
    let mut center_color = color;
    center_color[3] = (center_color[3] * intensity).clamp(0.0, 1.0);
    let mut edge_color = color;
    edge_color[3] = 0.0;
    append_radial_fan(mesh, coord, projection, radius, center_color, edge_color);
}

fn append_radial_fan(
    mesh: &mut VectorMeshData,
    coord: &GeoCoord,
    projection: CameraProjection,
    radius: f64,
    center_color: [f32; 4],
    edge_color: [f32; 4],
) {
    let center = projection.project(coord);
    let base = mesh.positions.len() as u32;
    mesh.positions.push([center.position.x, center.position.y, center.position.z]);
    mesh.colors.push(center_color);
    for i in 0..=DEFAULT_CIRCLE_SEGMENTS {
        let t = i as f64 / DEFAULT_CIRCLE_SEGMENTS as f64;
        let angle = std::f64::consts::TAU * t;
        mesh.positions.push([
            center.position.x + radius * angle.cos(),
            center.position.y + radius * angle.sin(),
            center.position.z,
        ]);
        mesh.colors.push(edge_color);
    }
    for i in 1..=DEFAULT_CIRCLE_SEGMENTS as u32 {
        mesh.indices.extend_from_slice(&[base, base + i, base + i + 1]);
    }
}

fn append_ring(
    mesh: &mut VectorMeshData,
    coord: &GeoCoord,
    projection: CameraProjection,
    inner_radius: f64,
    outer_radius: f64,
    color: [f32; 4],
) {
    if outer_radius <= inner_radius {
        return;
    }
    let center = projection.project(coord);
    let base = mesh.positions.len() as u32;
    for i in 0..=DEFAULT_CIRCLE_SEGMENTS {
        let t = i as f64 / DEFAULT_CIRCLE_SEGMENTS as f64;
        let angle = std::f64::consts::TAU * t;
        let (sin, cos) = angle.sin_cos();
        mesh.positions.push([
            center.position.x + inner_radius * cos,
            center.position.y + inner_radius * sin,
            center.position.z,
        ]);
        mesh.colors.push(color);
        mesh.positions.push([
            center.position.x + outer_radius * cos,
            center.position.y + outer_radius * sin,
            center.position.z,
        ]);
        mesh.colors.push(color);
    }
    for i in 0..DEFAULT_CIRCLE_SEGMENTS as u32 {
        let a = base + i * 2;
        mesh.indices.extend_from_slice(&[a, a + 1, a + 2, a + 1, a + 3, a + 2]);
    }
}

fn append_extruded_polygon(mesh: &mut VectorMeshData, coords: &[GeoCoord], projection: CameraProjection, style: &VectorStyle) {
    let ring = normalized_ring(coords);
    if ring.len() < 3 {
        return;
    }

    // --- Top surface ---
    let top_base = mesh.positions.len() as u32;
    for coord in &ring {
        let w = projection.project(coord);
        mesh.positions.push([
            w.position.x,
            w.position.y,
            coord.alt + style.extrusion_base as f64 + style.extrusion_height as f64,
        ]);
        mesh.colors.push(style.fill_color);
        mesh.normals.push([0.0, 0.0, 1.0]); // top face points up
    }
    for idx in tessellator::triangulate_polygon(&ring) {
        mesh.indices.push(top_base + idx);
    }

    // --- Side faces ---
    let side_color = [
        style.fill_color[0] * 0.75,
        style.fill_color[1] * 0.75,
        style.fill_color[2] * 0.75,
        style.fill_color[3],
    ];

    for i in 0..ring.len() {
        let a = &ring[i];
        let b = &ring[(i + 1) % ring.len()];
        let wa = projection.project(a);
        let wb = projection.project(b);
        let base_z_a = a.alt + style.extrusion_base as f64;
        let base_z_b = b.alt + style.extrusion_base as f64;
        let top_z_a = base_z_a + style.extrusion_height as f64;
        let top_z_b = base_z_b + style.extrusion_height as f64;

        // Outward-facing normal for this wall quad.
        // Edge direction: a→b in the XY plane.  Normal = perpendicular in XY, no Z.
        let dx = (wb.position.x - wa.position.x) as f32;
        let dy = (wb.position.y - wa.position.y) as f32;
        let len = (dx * dx + dy * dy).sqrt().max(1e-12);
        let normal = [dy / len, -dx / len, 0.0];

        let base = mesh.positions.len() as u32;
        mesh.positions.push([wa.position.x, wa.position.y, base_z_a]);
        mesh.positions.push([wb.position.x, wb.position.y, base_z_b]);
        mesh.positions.push([wb.position.x, wb.position.y, top_z_b]);
        mesh.positions.push([wa.position.x, wa.position.y, top_z_a]);
        for _ in 0..4 {
            mesh.colors.push(side_color);
            mesh.normals.push(normal);
        }
        mesh.indices.extend_from_slice(&[base, base + 1, base + 2, base, base + 2, base + 3]);
    }
}

fn normalized_ring(coords: &[GeoCoord]) -> Vec<GeoCoord> {
    if coords.len() > 1 {
        let first = coords.first().expect("ring first");
        let last = coords.last().expect("ring last");
        if (first.lat - last.lat).abs() < 1e-12
            && (first.lon - last.lon).abs() < 1e-12
            && (first.alt - last.alt).abs() < 1e-6
        {
            return coords[..coords.len() - 1].to_vec();
        }
    }
    coords.to_vec()
}

// ---------------------------------------------------------------------------
// Terrain draping (module-private)
// ---------------------------------------------------------------------------

/// Recursively drape all coordinates in a geometry onto terrain.
fn drape_geometry(geometry: &mut Geometry, terrain: &TerrainManager) {
    match geometry {
        Geometry::Point(p) => {
            if let Some(elev) = terrain.elevation_at(&p.coord) {
                p.coord.alt = elev;
            }
        }
        Geometry::LineString(ls) => {
            drape_coords(&mut ls.coords, terrain);
        }
        Geometry::Polygon(poly) => {
            drape_coords(&mut poly.exterior, terrain);
            for hole in &mut poly.interiors {
                drape_coords(hole, terrain);
            }
        }
        Geometry::MultiPoint(mp) => {
            for p in &mut mp.points {
                if let Some(elev) = terrain.elevation_at(&p.coord) {
                    p.coord.alt = elev;
                }
            }
        }
        Geometry::MultiLineString(mls) => {
            for ls in &mut mls.lines {
                drape_coords(&mut ls.coords, terrain);
            }
        }
        Geometry::MultiPolygon(mpoly) => {
            for poly in &mut mpoly.polygons {
                drape_coords(&mut poly.exterior, terrain);
                for hole in &mut poly.interiors {
                    drape_coords(hole, terrain);
                }
            }
        }
        Geometry::GeometryCollection(geoms) => {
            for g in geoms {
                drape_geometry(g, terrain);
            }
        }
    }
}

/// Drape a coordinate slice onto terrain.
fn drape_coords(coords: &mut [GeoCoord], terrain: &TerrainManager) {
    for coord in coords.iter_mut() {
        if let Some(elev) = terrain.elevation_at(coord) {
            coord.alt = elev;
        }
    }
}

// ---------------------------------------------------------------------------
// Layer trait implementation
// ---------------------------------------------------------------------------

impl Layer for VectorLayer {
    fn id(&self) -> LayerId {
        self.id
    }

    fn kind(&self) -> crate::layer::LayerKind {
        crate::layer::LayerKind::Vector
    }

    fn name(&self) -> &str {
        &self.name
    }

    fn visible(&self) -> bool {
        self.visible
    }

    fn set_visible(&mut self, visible: bool) {
        self.visible = visible;
    }

    fn opacity(&self) -> f32 {
        self.opacity
    }

    fn set_opacity(&mut self, opacity: f32) {
        self.opacity = opacity.clamp(0.0, 1.0);
    }

    fn as_any(&self) -> &dyn Any {
        self
    }

    fn as_any_mut(&mut self) -> &mut dyn Any {
        self
    }
}

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

#[cfg(test)]
mod tests {
    use super::*;
    use crate::geometry::{
        Feature, LineString, MultiLineString, MultiPoint, MultiPolygon, Point, Polygon,
    };
    use crate::layer::Layer;
    use crate::camera_projection::CameraProjection;
    use crate::terrain::{FlatElevationSource, TerrainConfig, TerrainManager};
    use rustial_math::{WebMercator, WorldBounds, WorldCoord};
    use std::collections::HashMap;

    // =====================================================================
    // Helpers
    // =====================================================================

    fn make_layer(geometry: Geometry) -> VectorLayer {
        let features = FeatureCollection {
            features: vec![Feature {
                geometry,
                properties: HashMap::new(),
            }],
        };
        VectorLayer::new("test", features, VectorStyle::default())
    }

    fn square_polygon() -> Polygon {
        Polygon {
            exterior: vec![
                GeoCoord::from_lat_lon(0.0, 0.0),
                GeoCoord::from_lat_lon(0.0, 1.0),
                GeoCoord::from_lat_lon(1.0, 1.0),
                GeoCoord::from_lat_lon(1.0, 0.0),
            ],
            interiors: vec![],
        }
    }

    fn two_point_line() -> LineString {
        LineString {
            coords: vec![
                GeoCoord::from_lat_lon(0.0, 0.0),
                GeoCoord::from_lat_lon(0.0, 1.0),
            ],
        }
    }

    fn origin_point() -> Point {
        Point {
            coord: GeoCoord::from_lat_lon(0.0, 0.0),
        }
    }

    fn flat_terrain_manager() -> TerrainManager {
        let config = TerrainConfig {
            enabled: true,
            mesh_resolution: 4,
            source: Box::new(FlatElevationSource::new(4, 4)),
            ..TerrainConfig::default()
        };
        let mut mgr = TerrainManager::new(config, 100);
        let extent = WebMercator::max_extent();
        let bounds = WorldBounds::new(
            WorldCoord::new(-extent, -extent, 0.0),
            WorldCoord::new(extent, extent, 0.0),
        );
        // Two updates: first requests, second loads.
        mgr.update(&bounds, 0, (0.0, 0.0), CameraProjection::WebMercator, 10_000_000.0, 0.0);
        mgr.update(&bounds, 0, (0.0, 0.0), CameraProjection::WebMercator, 10_000_000.0, 0.0);
        mgr
    }

    // =====================================================================
    // Construction and queries
    // =====================================================================

    #[test]
    fn new_layer_defaults() {
        let layer = make_layer(Geometry::Point(origin_point()));
        assert_eq!(layer.name(), "test");
        assert!(layer.visible());
        assert!((layer.opacity() - 1.0).abs() < f32::EPSILON);
        assert_eq!(layer.feature_count(), 1);
        assert_eq!(layer.total_coords(), 1);
    }

    #[test]
    fn layer_trait_visibility() {
        let mut layer = make_layer(Geometry::Point(origin_point()));
        layer.set_visible(false);
        assert!(!layer.visible());
        layer.set_visible(true);
        assert!(layer.visible());
    }

    #[test]
    fn layer_trait_opacity_clamped() {
        let mut layer = make_layer(Geometry::Point(origin_point()));
        layer.set_opacity(1.5);
        assert!((layer.opacity() - 1.0).abs() < f32::EPSILON);
        layer.set_opacity(-0.5);
        assert!((layer.opacity() - 0.0).abs() < f32::EPSILON);
    }

    #[test]
    fn debug_impl() {
        let layer = make_layer(Geometry::Point(origin_point()));
        let dbg = format!("{layer:?}");
        assert!(dbg.contains("VectorLayer"));
        assert!(dbg.contains("test"));
    }

    // =====================================================================
    // Tessellation: Polygon
    // =====================================================================

    #[test]
    fn tessellate_polygon() {
        let layer = make_layer(Geometry::Polygon(square_polygon()));
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert_eq!(mesh.vertex_count(), 4);
        assert_eq!(mesh.index_count(), 6); // 2 triangles
        assert_eq!(mesh.triangle_count(), 2);
        assert_eq!(mesh.colors.len(), 4);
        assert!(!mesh.is_empty());
    }

    // =====================================================================
    // Tessellation: LineString
    // =====================================================================

    #[test]
    fn tessellate_linestring() {
        let layer = make_layer(Geometry::LineString(two_point_line()));
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert_eq!(mesh.vertex_count(), 4); // Ribbon quad
        assert_eq!(mesh.index_count(), 6);
    }

    // =====================================================================
    // Tessellation: Point
    // =====================================================================

    #[test]
    fn tessellate_point() {
        let layer = make_layer(Geometry::Point(origin_point()));
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert_eq!(mesh.vertex_count(), 4); // Quad
        assert_eq!(mesh.index_count(), 6); // 2 triangles
        // Fill colour should be used for points.
        assert_eq!(mesh.colors[0], VectorStyle::default().fill_color);
    }

    // =====================================================================
    // Tessellation: Multi* types
    // =====================================================================

    #[test]
    fn tessellate_multi_point() {
        let mp = Geometry::MultiPoint(MultiPoint {
            points: vec![origin_point(), origin_point()],
        });
        let layer = make_layer(mp);
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        // Two points = 2 quads = 8 vertices, 12 indices.
        assert_eq!(mesh.vertex_count(), 8);
        assert_eq!(mesh.index_count(), 12);
    }

    #[test]
    fn tessellate_multi_linestring() {
        let mls = Geometry::MultiLineString(MultiLineString {
            lines: vec![two_point_line(), two_point_line()],
        });
        let layer = make_layer(mls);
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert_eq!(mesh.vertex_count(), 8); // 2 ribbons x 4 verts
        assert_eq!(mesh.index_count(), 12);
    }

    #[test]
    fn tessellate_multi_polygon() {
        let mpoly = Geometry::MultiPolygon(MultiPolygon {
            polygons: vec![square_polygon(), square_polygon()],
        });
        let layer = make_layer(mpoly);
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert_eq!(mesh.vertex_count(), 8); // 2 quads x 4 verts
        assert_eq!(mesh.index_count(), 12);
    }

    #[test]
    fn tessellate_geometry_collection() {
        let gc = Geometry::GeometryCollection(vec![
            Geometry::Point(origin_point()),
            Geometry::Polygon(square_polygon()),
        ]);
        let layer = make_layer(gc);
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        // Point: 4 verts + 6 indices, Polygon: 4 verts + 6 indices.
        assert_eq!(mesh.vertex_count(), 8);
        assert_eq!(mesh.index_count(), 12);
    }

    // =====================================================================
    // Tessellation: empty / degenerate
    // =====================================================================

    #[test]
    fn tessellate_empty_collection() {
        let features = FeatureCollection { features: vec![] };
        let layer = VectorLayer::new("empty", features, VectorStyle::default());
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert!(mesh.is_empty());
        assert_eq!(mesh.vertex_count(), 0);
    }

    // =====================================================================
    // VectorMeshData helpers
    // =====================================================================

    #[test]
    fn mesh_data_merge() {
        let mut a = VectorMeshData {
            positions: vec![[0.0, 0.0, 0.0], [1.0, 0.0, 0.0]],
            colors: vec![[1.0, 0.0, 0.0, 1.0], [1.0, 0.0, 0.0, 1.0]],
            indices: vec![0, 1, 0],
            ..Default::default()
        };
        let b = VectorMeshData {
            positions: vec![[2.0, 0.0, 0.0], [3.0, 0.0, 0.0]],
            colors: vec![[0.0, 1.0, 0.0, 1.0], [0.0, 1.0, 0.0, 1.0]],
            indices: vec![0, 1, 0],
            ..Default::default()
        };
        a.merge(&b);
        assert_eq!(a.vertex_count(), 4);
        assert_eq!(a.index_count(), 6);
        // Merged indices should be offset by base=2.
        assert_eq!(a.indices, vec![0, 1, 0, 2, 3, 2]);
    }

    #[test]
    fn mesh_data_clear() {
        let mut mesh = VectorMeshData {
            positions: vec![[0.0, 0.0, 0.0]],
            colors: vec![[1.0, 0.0, 0.0, 1.0]],
            indices: vec![0],
            ..Default::default()
        };
        mesh.clear();
        assert!(mesh.is_empty());
        assert_eq!(mesh.vertex_count(), 0);
    }

    // =====================================================================
    // Terrain draping
    // =====================================================================

    #[test]
    fn drape_sets_altitude() {
        let mgr = flat_terrain_manager();

        let features = FeatureCollection {
            features: vec![Feature {
                geometry: Geometry::Point(Point {
                    coord: GeoCoord::new(10.0, 20.0, 999.0),
                }),
                properties: HashMap::new(),
            }],
        };

        let mut layer = VectorLayer::new("test", features, VectorStyle::default());
        layer.drape_on_terrain(&mgr);

        // Flat terrain -> altitude should be 0.
        match &layer.features.features[0].geometry {
            Geometry::Point(p) => assert!((p.coord.alt - 0.0).abs() < 1e-3),
            _ => panic!("expected Point"),
        }
    }

    #[test]
    fn drape_skipped_when_terrain_disabled() {
        let config = TerrainConfig::default(); // enabled = false
        let mgr = TerrainManager::new(config, 100);

        let features = FeatureCollection {
            features: vec![Feature {
                geometry: Geometry::Point(Point {
                    coord: GeoCoord::new(10.0, 20.0, 999.0),
                }),
                properties: HashMap::new(),
            }],
        };

        let mut layer = VectorLayer::new("test", features, VectorStyle::default());
        layer.drape_on_terrain(&mgr);

        // Altitude should remain unchanged.
        match &layer.features.features[0].geometry {
            Geometry::Point(p) => assert!((p.coord.alt - 999.0).abs() < 1e-3),
            _ => panic!("expected Point"),
        }
    }

    #[test]
    fn drape_linestring_coords() {
        let mgr = flat_terrain_manager();

        let features = FeatureCollection {
            features: vec![Feature {
                geometry: Geometry::LineString(LineString {
                    coords: vec![
                        GeoCoord::new(10.0, 20.0, 500.0),
                        GeoCoord::new(11.0, 21.0, 600.0),
                    ],
                }),
                properties: HashMap::new(),
            }],
        };

        let mut layer = VectorLayer::new("test", features, VectorStyle::default());
        layer.drape_on_terrain(&mgr);

        match &layer.features.features[0].geometry {
            Geometry::LineString(ls) => {
                for coord in &ls.coords {
                    assert!(
                        coord.alt.abs() < 1e-3,
                        "expected flat terrain, got alt={}",
                        coord.alt
                    );
                }
            }
            _ => panic!("expected LineString"),
        }
    }

    #[test]
    fn tessellate_circle_mode() {
        let mut style = VectorStyle::default();
        style.render_mode = VectorRenderMode::Circle;
        let layer = make_layer(Geometry::Point(origin_point()));
        let layer = VectorLayer::new("circle", layer.features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert!(mesh.vertex_count() > 8);
        assert!(mesh.index_count() >= DEFAULT_CIRCLE_SEGMENTS * 3);
    }

    #[test]
    fn tessellate_heatmap_mode_has_faded_edges() {
        let mut style = VectorStyle::heatmap([1.0, 0.0, 0.0, 0.5], 24.0, 1.0);
        style.render_mode = VectorRenderMode::Heatmap;
        let layer = make_layer(Geometry::Point(origin_point()));
        let layer = VectorLayer::new("heatmap", layer.features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert_eq!(mesh.colors.first().map(|c| c[3]), Some(0.5));
        assert_eq!(mesh.colors.last().map(|c| c[3]), Some(0.0));
    }

    #[test]
    fn tessellate_fill_extrusion_mode_produces_vertical_geometry() {
        let style = VectorStyle::fill_extrusion([0.5, 0.5, 0.8, 1.0], 0.0, 50.0);
        let layer = make_layer(Geometry::Polygon(square_polygon()));
        let layer = VectorLayer::new("extrusion", layer.features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        let min_z = mesh.positions.iter().map(|p| p[2]).fold(f64::INFINITY, f64::min);
        let max_z = mesh.positions.iter().map(|p| p[2]).fold(f64::NEG_INFINITY, f64::max);
        assert!(max_z > min_z);
    }

    #[test]
    fn fill_extrusion_tessellation_produces_normals() {
        let style = VectorStyle::fill_extrusion([0.5, 0.5, 0.8, 1.0], 0.0, 50.0);
        let layer = make_layer(Geometry::Polygon(square_polygon()));
        let layer = VectorLayer::new("extrusion", layer.features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);

        assert!(mesh.has_normals());
        assert_eq!(mesh.normals.len(), mesh.positions.len());
        assert_eq!(mesh.render_mode, VectorRenderMode::FillExtrusion);
    }

    #[test]
    fn fill_extrusion_top_normals_point_up() {
        let style = VectorStyle::fill_extrusion([1.0, 0.0, 0.0, 1.0], 0.0, 100.0);
        let layer = make_layer(Geometry::Polygon(square_polygon()));
        let layer = VectorLayer::new("extrusion", layer.features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);

        // The top surface vertices are the first `ring.len()` vertices.
        // Their normals should all point straight up: [0, 0, 1].
        let ring_len = 4; // square has 4 unique vertices
        for i in 0..ring_len {
            let n = mesh.normals[i];
            assert!((n[0]).abs() < 1e-6, "top normal x should be 0, got {}", n[0]);
            assert!((n[1]).abs() < 1e-6, "top normal y should be 0, got {}", n[1]);
            assert!((n[2] - 1.0).abs() < 1e-6, "top normal z should be 1, got {}", n[2]);
        }
    }

    #[test]
    fn fill_extrusion_side_normals_are_horizontal() {
        let style = VectorStyle::fill_extrusion([1.0, 0.0, 0.0, 1.0], 0.0, 100.0);
        let layer = make_layer(Geometry::Polygon(square_polygon()));
        let layer = VectorLayer::new("extrusion", layer.features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);

        // Side faces start after the top ring vertices.
        let ring_len = 4;
        for i in ring_len..mesh.normals.len() {
            let n = mesh.normals[i];
            // Side normals have Z = 0 (horizontal).
            assert!((n[2]).abs() < 1e-6, "side normal z should be 0, got {} at vertex {}", n[2], i);
            // And should be unit length in XY.
            let len = (n[0] * n[0] + n[1] * n[1]).sqrt();
            assert!((len - 1.0).abs() < 0.01, "side normal length should be ~1, got {} at vertex {}", len, i);
        }
    }

    #[test]
    fn flat_fill_tessellation_has_no_normals() {
        let style = VectorStyle {
            render_mode: VectorRenderMode::Fill,
            fill_color: [0.0, 1.0, 0.0, 1.0],
            ..VectorStyle::default()
        };
        let layer = make_layer(Geometry::Polygon(square_polygon()));
        let layer = VectorLayer::new("fill", layer.features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);

        assert!(!mesh.has_normals());
        assert!(mesh.normals.is_empty());
        assert_eq!(mesh.render_mode, VectorRenderMode::Fill);
    }

    #[test]
    fn symbol_candidates_point_placement_skips_lines() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Road".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::LineString(two_point_line()),
                    properties,
                }],
            },
            style,
        );

        assert!(layer.symbol_candidates().is_empty());
    }

    #[test]
    fn symbol_candidates_text_only_use_text_overlap_flag() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_text_allow_overlap = true;
        style.symbol_icon_allow_overlap = false;

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Label".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 1);
        assert!(candidates[0].allow_overlap);
    }

    #[test]
    fn symbol_candidates_use_fixed_text_anchor_when_variable_anchors_absent() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_text_anchor = SymbolAnchor::TopRight;
        style.symbol_anchors = vec![SymbolAnchor::TopRight];

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Label".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 1);
        assert_eq!(candidates[0].anchors, vec![SymbolAnchor::TopRight]);
    }

    #[test]
    fn symbol_candidates_propagate_text_radial_offset() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_text_anchor = SymbolAnchor::Top;
        style.symbol_anchors = vec![SymbolAnchor::Top];
        style.symbol_text_radial_offset = Some(2.0);

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Label".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 1);
        assert_eq!(candidates[0].radial_offset, Some(2.0));
    }

    #[test]
    fn symbol_candidates_propagate_text_max_width() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_text_max_width = Some(6.0);

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Long label".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 1);
        assert_eq!(candidates[0].text_max_width, Some(6.0));
    }

    #[test]
    fn symbol_candidates_propagate_text_line_height() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_text_line_height = Some(1.5);

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Long label".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 1);
        assert_eq!(candidates[0].text_line_height, Some(1.5));
    }

    #[test]
    fn symbol_candidates_propagate_text_letter_spacing() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_text_letter_spacing = Some(0.25);

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Long label".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 1);
        assert_eq!(candidates[0].text_letter_spacing, Some(0.25));
    }

    #[test]
    fn symbol_candidates_apply_uppercase_text_transform() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_text_transform = SymbolTextTransform::Uppercase;

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Main Street".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 1);
        assert_eq!(candidates[0].text.as_deref(), Some("MAIN STREET"));
    }

    #[test]
    fn symbol_candidates_apply_lowercase_text_transform() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_text_transform = SymbolTextTransform::Lowercase;

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Main Street".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 1);
        assert_eq!(candidates[0].text.as_deref(), Some("main street"));
    }

    #[test]
    fn symbol_candidates_keep_variable_anchor_priority_over_fixed_anchor() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_text_anchor = SymbolAnchor::BottomLeft;
        style.symbol_anchors = vec![SymbolAnchor::Center, SymbolAnchor::Top];

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Label".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 1);
        assert_eq!(candidates[0].anchors, vec![SymbolAnchor::Center, SymbolAnchor::Top]);
    }

    #[test]
    fn symbol_candidates_use_variable_anchor_offset_order_when_present() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_text_anchor = SymbolAnchor::BottomLeft;
        style.symbol_anchors = vec![SymbolAnchor::Center];
        style.symbol_variable_anchor_offsets = Some(vec![
            (SymbolAnchor::Top, [1.0, 2.0]),
            (SymbolAnchor::Right, [3.0, 4.0]),
        ]);

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Label".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 1);
        assert_eq!(candidates[0].anchors, vec![SymbolAnchor::Top, SymbolAnchor::Right]);
        assert_eq!(
            candidates[0].variable_anchor_offsets,
            Some(vec![
                (SymbolAnchor::Top, [1.0, 2.0]),
                (SymbolAnchor::Right, [3.0, 4.0]),
            ])
        );
    }

    #[test]
    fn symbol_candidates_text_and_icon_require_both_overlap_flags() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_icon_image = Some("marker".to_owned());
        style.symbol_text_allow_overlap = true;
        style.symbol_icon_allow_overlap = false;

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Label".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 1);
        assert!(!candidates[0].allow_overlap);
    }

    #[test]
    fn symbol_candidates_text_only_use_text_ignore_placement_flag() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_text_ignore_placement = true;
        style.symbol_icon_ignore_placement = false;

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Label".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 1);
        assert!(candidates[0].ignore_placement);
    }

    #[test]
    fn symbol_candidates_text_and_icon_require_both_ignore_flags() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_icon_image = Some("marker".to_owned());
        style.symbol_text_ignore_placement = true;
        style.symbol_icon_ignore_placement = false;

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Label".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 1);
        assert!(!candidates[0].ignore_placement);
    }

    #[test]
    fn symbol_candidates_emit_icon_fallback_when_text_is_optional() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_icon_image = Some("marker".to_owned());
        style.symbol_text_optional = true;

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Label".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 2);
        assert_eq!(candidates[0].text.as_deref(), Some("Label"));
        assert_eq!(candidates[0].icon_image.as_deref(), Some("marker"));
        assert!(candidates[1].text.is_none());
        assert_eq!(candidates[1].icon_image.as_deref(), Some("marker"));
        assert_eq!(candidates[0].cross_tile_id, candidates[1].cross_tile_id);
        assert_eq!(candidates[0].placement_group_id, candidates[1].placement_group_id);
    }

    #[test]
    fn symbol_candidates_emit_text_fallback_when_icon_is_optional() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_icon_image = Some("marker".to_owned());
        style.symbol_icon_optional = true;

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Label".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::Point(origin_point()),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert_eq!(candidates.len(), 2);
        assert_eq!(candidates[0].text.as_deref(), Some("Label"));
        assert_eq!(candidates[0].icon_image.as_deref(), Some("marker"));
        assert_eq!(candidates[1].text.as_deref(), Some("Label"));
        assert!(candidates[1].icon_image.is_none());
        assert_eq!(candidates[0].cross_tile_id, candidates[1].cross_tile_id);
        assert_eq!(candidates[0].placement_group_id, candidates[1].placement_group_id);
    }

    #[test]
    fn symbol_candidates_line_placement_repeats_anchors_with_spacing() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_placement = SymbolPlacement::Line;
        style.symbol_spacing = 1000.0;

        let start = GeoCoord::from_lat_lon(0.0, 0.0);
        let end = GeoCoord::from_lat_lon(0.0, 0.05);
        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Road".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::LineString(LineString {
                        coords: vec![start, end],
                    }),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert!(candidates.len() > 1, "longer lines should produce repeated anchors");
        assert!(candidates.iter().all(|candidate| (candidate.anchor.lat - 0.0).abs() < 1e-9));
        assert!(candidates.windows(2).all(|pair| pair[0].anchor.lon < pair[1].anchor.lon));
        assert!(candidates.iter().all(|candidate| candidate.rotation_rad.abs() < 1e-6));
        assert_eq!(candidates[0].text.as_deref(), Some("Road"));
    }

    #[test]
    fn symbol_candidates_line_placement_rotates_vertical_lines() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_placement = SymbolPlacement::Line;

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("North".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::LineString(LineString {
                        coords: vec![
                            GeoCoord::from_lat_lon(0.0, 0.0),
                            GeoCoord::from_lat_lon(1.0, 0.0),
                        ],
                    }),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert!(!candidates.is_empty());
        assert!(candidates.iter().all(|candidate| {
            (candidate.rotation_rad.abs() - std::f32::consts::FRAC_PI_2).abs() < 0.05
        }));
    }

    #[test]
    fn symbol_candidates_line_placement_keeps_reversed_lines_upright() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_placement = SymbolPlacement::Line;
        style.symbol_keep_upright = true;

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("West".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::LineString(LineString {
                        coords: vec![
                            GeoCoord::from_lat_lon(0.0, 1.0),
                            GeoCoord::from_lat_lon(0.0, 0.0),
                        ],
                    }),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert!(!candidates.is_empty());
        assert!(candidates.iter().all(|candidate| candidate.rotation_rad.abs() < 0.05));
    }

    #[test]
    fn symbol_candidates_line_placement_can_disable_keep_upright() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_placement = SymbolPlacement::Line;
        style.symbol_keep_upright = false;

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("West".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::LineString(LineString {
                        coords: vec![
                            GeoCoord::from_lat_lon(0.0, 1.0),
                            GeoCoord::from_lat_lon(0.0, 0.0),
                        ],
                    }),
                    properties,
                }],
            },
            style,
        );

        let candidates = layer.symbol_candidates();
        assert!(!candidates.is_empty());
        assert!(candidates.iter().all(|candidate| {
            (candidate.rotation_rad.abs() - std::f32::consts::PI).abs() < 0.05
        }));
    }

    #[test]
    fn symbol_candidates_line_placement_cross_tile_id_stays_stable_across_small_anchor_shifts() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_placement = SymbolPlacement::Line;
        style.symbol_spacing = 1000.0;

        let mut properties = HashMap::new();
        properties.insert("id".to_owned(), crate::geometry::PropertyValue::String("road-1".to_owned()));
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Main".to_owned()));

        let base = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::LineString(LineString {
                        coords: vec![
                            GeoCoord::from_lat_lon(0.0, 0.0),
                            GeoCoord::from_lat_lon(0.0, 0.05),
                        ],
                    }),
                    properties: properties.clone(),
                }],
            },
            style.clone(),
        );
        let shifted = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::LineString(LineString {
                        coords: vec![
                            GeoCoord::from_lat_lon(0.0, 0.0),
                            GeoCoord::from_lat_lon(0.0002, 0.0502),
                        ],
                    }),
                    properties,
                }],
            },
            style,
        );

        let base_ids = base
            .symbol_candidates()
            .into_iter()
            .map(|candidate| candidate.cross_tile_id)
            .collect::<Vec<_>>();
        let shifted_ids = shifted
            .symbol_candidates()
            .into_iter()
            .map(|candidate| candidate.cross_tile_id)
            .collect::<Vec<_>>();

        assert_eq!(base_ids, shifted_ids);
    }

    #[test]
    fn symbol_candidates_line_placement_cross_tile_id_changes_for_shifted_line_windows() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_placement = SymbolPlacement::Line;
        style.symbol_spacing = 1000.0;

        let mut properties = HashMap::new();
        properties.insert("id".to_owned(), crate::geometry::PropertyValue::String("road-2".to_owned()));
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Main".to_owned()));

        let base = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::LineString(LineString {
                        coords: vec![
                            GeoCoord::from_lat_lon(0.0, 0.0),
                            GeoCoord::from_lat_lon(0.0, 0.05),
                        ],
                    }),
                    properties: properties.clone(),
                }],
            },
            style.clone(),
        );
        let shifted_window = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::LineString(LineString {
                        coords: vec![
                            GeoCoord::from_lat_lon(0.0, 0.01),
                            GeoCoord::from_lat_lon(0.0, 0.06),
                        ],
                    }),
                    properties,
                }],
            },
            style,
        );

        let base_ids = base
            .symbol_candidates()
            .into_iter()
            .map(|candidate| candidate.cross_tile_id)
            .collect::<Vec<_>>();
        let shifted_ids = shifted_window
            .symbol_candidates()
            .into_iter()
            .map(|candidate| candidate.cross_tile_id)
            .collect::<Vec<_>>();

        assert_ne!(base_ids.first(), shifted_ids.first());
        assert!(base_ids.iter().any(|id| shifted_ids.contains(id)));
    }

    #[test]
    fn symbol_candidates_line_placement_filters_sharp_turns_with_max_angle() {
        let mut style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        style.symbol_text_field = Some("name".to_owned());
        style.symbol_placement = SymbolPlacement::Line;
        style.symbol_spacing = 10_000.0;
        style.symbol_max_angle = 10.0;

        let mut properties = HashMap::new();
        properties.insert("name".to_owned(), crate::geometry::PropertyValue::String("Turn".to_owned()));
        let layer = VectorLayer::new(
            "symbol",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::LineString(LineString {
                        coords: vec![
                            GeoCoord::from_lat_lon(0.0, 0.0),
                            GeoCoord::from_lat_lon(0.0, 0.03),
                            GeoCoord::from_lat_lon(0.03, 0.03),
                        ],
                    }),
                    properties,
                }],
            },
            style,
        );

        assert!(layer.symbol_candidates().is_empty());
    }

    #[test]
    fn tessellate_symbol_mode_stacks_halo_and_fill() {
        let style = VectorStyle::symbol([0.1, 0.2, 0.9, 1.0], [1.0, 1.0, 1.0, 1.0], 8.0);
        let layer = make_layer(Geometry::Point(origin_point()));
        let layer = VectorLayer::new("symbol", layer.features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert_eq!(mesh.vertex_count(), 8);
        assert_eq!(mesh.index_count(), 12);
    }

    #[test]
    fn tessellate_equirectangular_changes_xy_positions() {
        let layer = make_layer(Geometry::Polygon(square_polygon()));
        let merc = layer.tessellate(CameraProjection::WebMercator);
        let eq = layer.tessellate(CameraProjection::Equirectangular);

        assert_eq!(merc.positions.len(), eq.positions.len());
        assert!(merc
            .positions
            .iter()
            .zip(eq.positions.iter())
            .any(|(a, b)| (a[0] - b[0]).abs() > 1.0 || (a[1] - b[1]).abs() > 1.0));
    }

    // =====================================================================
    // Line-mode tessellation: cap/join/dash pipeline
    // =====================================================================

    #[test]
    fn tessellate_line_mode_populates_normals_and_distances() {
        let style = VectorStyle::line([1.0, 0.0, 0.0, 1.0], 4.0);
        let layer = VectorLayer::new("line", make_layer(Geometry::LineString(two_point_line())).features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert!(!mesh.is_empty());
        assert_eq!(mesh.line_normals.len(), mesh.positions.len(),
            "line_normals must have one entry per vertex");
        assert_eq!(mesh.line_distances.len(), mesh.positions.len(),
            "line_distances must have one entry per vertex");
        // At least one distance should be > 0 (the endpoint).
        assert!(mesh.line_distances.iter().any(|&d| d > 0.0),
            "at least one distance should be positive");
    }

    #[test]
    fn tessellate_line_mode_propagates_dash_params() {
        let style = VectorStyle::line_styled(
            [1.0, 0.0, 0.0, 1.0],
            4.0,
            LineCap::Round,
            LineJoin::Bevel,
            2.0,
            Some(vec![10.0, 5.0]),
        );
        let layer = VectorLayer::new("dashed", make_layer(Geometry::LineString(two_point_line())).features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert_eq!(mesh.line_params[0], 10.0, "dash_length");
        assert_eq!(mesh.line_params[1], 5.0, "gap_length");
        assert_eq!(mesh.line_params[2], 1.0, "cap_round flag");
    }

    #[test]
    fn tessellate_line_mode_round_join_adds_vertices() {
        let line = crate::geometry::LineString {
            coords: vec![
                GeoCoord::from_lat_lon(0.0, 0.0),
                GeoCoord::from_lat_lon(0.0, 1.0),
                GeoCoord::from_lat_lon(1.0, 1.0),
            ],
        };
        let miter_style = VectorStyle::line_styled(
            [1.0, 0.0, 0.0, 1.0], 4.0,
            LineCap::Butt, LineJoin::Miter, 10.0, None,
        );
        let round_style = VectorStyle::line_styled(
            [1.0, 0.0, 0.0, 1.0], 4.0,
            LineCap::Butt, LineJoin::Round, 2.0, None,
        );
        let miter_layer = VectorLayer::new("m", make_layer(Geometry::LineString(line.clone())).features, miter_style);
        let round_layer = VectorLayer::new("r", make_layer(Geometry::LineString(line)).features, round_style);
        let miter_mesh = miter_layer.tessellate(CameraProjection::WebMercator);
        let round_mesh = round_layer.tessellate(CameraProjection::WebMercator);
        assert!(
            round_mesh.vertex_count() > miter_mesh.vertex_count(),
            "round join should produce more vertices than miter: {} vs {}",
            round_mesh.vertex_count(), miter_mesh.vertex_count(),
        );
    }

    // =====================================================================
    // Data-driven per-feature line width and colour
    // =====================================================================

    /// Build a two-feature line layer where each feature has a `"width"`
    /// property (narrow = 2.0, wide = 10.0) sharing a single VectorStyle
    /// with a data-driven width expression.
    fn two_feature_dd_width_layer() -> VectorLayer {
        use crate::geometry::PropertyValue;

        let narrow_feature = Feature {
            geometry: Geometry::LineString(two_point_line()),
            properties: {
                let mut p = HashMap::new();
                p.insert("width".into(), PropertyValue::Number(2.0));
                p
            },
        };
        let wide_feature = Feature {
            geometry: Geometry::LineString(two_point_line()),
            properties: {
                let mut p = HashMap::new();
                p.insert("width".into(), PropertyValue::Number(10.0));
                p
            },
        };
        let features = FeatureCollection {
            features: vec![narrow_feature, wide_feature],
        };

        let mut style = VectorStyle::line([1.0, 0.0, 0.0, 1.0], 2.0);
        style.width_expr = Some(Expression::GetProperty {
            key: "width".into(),
            fallback: 2.0,
        });
        style.eval_zoom = 10.0;

        VectorLayer::new("dd_width", features, style)
    }

    #[test]
    fn data_driven_width_produces_different_ribbon_widths() {
        let layer = two_feature_dd_width_layer();
        let mesh = layer.tessellate(CameraProjection::WebMercator);

        // Both features should be tessellated (non-empty).
        assert!(!mesh.is_empty());

        // Now tessellate each feature individually to compare widths.
        let narrow_style = VectorStyle::line([1.0, 0.0, 0.0, 1.0], 2.0);
        let wide_style = VectorStyle::line([1.0, 0.0, 0.0, 1.0], 10.0);

        let narrow_layer = VectorLayer::new(
            "narrow",
            FeatureCollection {
                features: vec![layer.features.features[0].clone()],
            },
            narrow_style,
        );
        let wide_layer = VectorLayer::new(
            "wide",
            FeatureCollection {
                features: vec![layer.features.features[1].clone()],
            },
            wide_style,
        );

        let narrow_mesh = narrow_layer.tessellate(CameraProjection::WebMercator);
        let wide_mesh = wide_layer.tessellate(CameraProjection::WebMercator);

        // Narrow ribbon should have smaller span than wide ribbon.
        let narrow_span = position_y_span(&narrow_mesh);
        let wide_span = position_y_span(&wide_mesh);
        assert!(
            wide_span > narrow_span,
            "wide ribbon span ({wide_span}) must exceed narrow ribbon span ({narrow_span})",
        );

        // The combined data-driven mesh should have vertices spanning at
        // least as wide as the widest individual ribbon.
        let combined_span = position_y_span(&mesh);
        assert!(
            combined_span >= wide_span * 0.99,
            "combined mesh span ({combined_span}) should be >= wide span ({wide_span})",
        );
    }

    #[test]
    fn data_driven_color_assigns_per_feature_colors() {
        use crate::geometry::PropertyValue;

        let red_feature = Feature {
            geometry: Geometry::LineString(two_point_line()),
            properties: {
                let mut p = HashMap::new();
                p.insert("kind".into(), PropertyValue::String("highway".into()));
                p
            },
        };
        let blue_feature = Feature {
            geometry: Geometry::LineString(two_point_line()),
            properties: {
                let mut p = HashMap::new();
                p.insert("kind".into(), PropertyValue::String("local".into()));
                p
            },
        };
        let features = FeatureCollection {
            features: vec![red_feature, blue_feature],
        };

        let mut style = VectorStyle::line([1.0, 0.0, 0.0, 1.0], 4.0);
        style.stroke_color_expr = Some(Expression::Match {
            input: Box::new(crate::expression::StringExpression::GetProperty {
                key: "kind".into(),
                fallback: String::new(),
            }),
            cases: vec![
                ("highway".into(), [1.0, 0.0, 0.0, 1.0]),
                ("local".into(), [0.0, 0.0, 1.0, 1.0]),
            ],
            fallback: [0.5, 0.5, 0.5, 1.0],
        });
        style.eval_zoom = 10.0;

        let layer = VectorLayer::new("dd_color", features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);

        assert!(!mesh.is_empty());

        // Vertices should contain both red and blue colors.
        let has_red = mesh.colors.iter().any(|c| c[0] > 0.9 && c[1] < 0.1 && c[2] < 0.1);
        let has_blue = mesh.colors.iter().any(|c| c[0] < 0.1 && c[1] < 0.1 && c[2] > 0.9);
        assert!(has_red, "mesh should contain red vertices from highway feature");
        assert!(has_blue, "mesh should contain blue vertices from local feature");
    }

    #[test]
    fn non_data_driven_width_expr_uses_uniform_value() {
        // A constant expression is NOT data-driven; the fast path should
        // apply the uniform stroke_width to all features.
        let features = FeatureCollection {
            features: vec![
                Feature {
                    geometry: Geometry::LineString(two_point_line()),
                    properties: HashMap::new(),
                },
                Feature {
                    geometry: Geometry::LineString(two_point_line()),
                    properties: HashMap::new(),
                },
            ],
        };
        let mut style = VectorStyle::line([1.0, 0.0, 0.0, 1.0], 4.0);
        style.width_expr = Some(Expression::Constant(4.0));
        style.eval_zoom = 10.0;

        let layer = VectorLayer::new("uniform", features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert!(!mesh.is_empty());

        // All vertices should have the same color (uniform path).
        let first_color = mesh.colors[0];
        assert!(mesh.colors.iter().all(|c| *c == first_color));
    }

    #[test]
    fn data_driven_width_fingerprint_changes_with_zoom() {
        let mut style = VectorStyle::line([1.0, 0.0, 0.0, 1.0], 4.0);
        style.width_expr = Some(Expression::GetProperty {
            key: "width".into(),
            fallback: 4.0,
        });

        style.eval_zoom = 5.0;
        let fp1 = style.tessellation_fingerprint();

        style.eval_zoom = 10.0;
        let fp2 = style.tessellation_fingerprint();

        assert_ne!(fp1, fp2, "data-driven fingerprint should differ by zoom");
    }

    /// Compute the Y-axis extent of all positions in a mesh.
    fn position_y_span(mesh: &VectorMeshData) -> f64 {
        let ys: Vec<f64> = mesh.positions.iter().map(|p| p[1]).collect();
        let min = ys.iter().cloned().fold(f64::INFINITY, f64::min);
        let max = ys.iter().cloned().fold(f64::NEG_INFINITY, f64::max);
        max - min
    }

    // =====================================================================
    // Line gradient tests
    // =====================================================================

    fn blue_to_red_ramp() -> crate::visualization::ColorRamp {
        use crate::visualization::{ColorRamp, ColorStop};
        ColorRamp::new(vec![
            ColorStop { value: 0.0, color: [0.0, 0.0, 1.0, 1.0] },
            ColorStop { value: 1.0, color: [1.0, 0.0, 0.0, 1.0] },
        ])
    }

    #[test]
    fn line_gradient_overrides_vertex_colors() {
        let ramp = blue_to_red_ramp();
        let style = VectorStyle::line_gradient(4.0, ramp);
        let layer = VectorLayer::new(
            "grad",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::LineString(LineString {
                        coords: vec![
                            GeoCoord::from_lat_lon(0.0, 0.0),
                            GeoCoord::from_lat_lon(0.0, 1.0),
                        ],
                    }),
                    properties: HashMap::new(),
                }],
            },
            style,
        );
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert!(!mesh.colors.is_empty());
        // Start vertices should be blueish (distance ~0 → t ≈ 0).
        // End vertices should be reddish (distance ~max → t ≈ 1).
        let has_blue = mesh.colors.iter().any(|c| c[2] > 0.8 && c[0] < 0.2);
        let has_red = mesh.colors.iter().any(|c| c[0] > 0.8 && c[2] < 0.2);
        assert!(has_blue, "expected some blue-ish vertices near start");
        assert!(has_red, "expected some red-ish vertices near end");
    }

    #[test]
    fn line_gradient_without_ramp_uses_solid_color() {
        let solid = [0.5, 0.5, 0.5, 1.0];
        let style = VectorStyle::line(solid, 4.0);
        let layer = VectorLayer::new(
            "solid",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::LineString(LineString {
                        coords: vec![
                            GeoCoord::from_lat_lon(0.0, 0.0),
                            GeoCoord::from_lat_lon(0.0, 1.0),
                        ],
                    }),
                    properties: HashMap::new(),
                }],
            },
            style,
        );
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert!(!mesh.colors.is_empty());
        for c in &mesh.colors {
            assert_eq!(*c, solid, "all vertices should share the solid colour");
        }
    }

    #[test]
    fn line_gradient_midpoint_is_interpolated() {
        use crate::visualization::{ColorRamp, ColorStop};
        let ramp = ColorRamp::new(vec![
            ColorStop { value: 0.0, color: [0.0, 0.0, 0.0, 1.0] },
            ColorStop { value: 1.0, color: [1.0, 1.0, 1.0, 1.0] },
        ]);
        let style = VectorStyle::line_gradient(2.0, ramp);
        let layer = VectorLayer::new(
            "mid",
            FeatureCollection {
                features: vec![Feature {
                    geometry: Geometry::LineString(LineString {
                        coords: vec![
                            GeoCoord::from_lat_lon(0.0, 0.0),
                            GeoCoord::from_lat_lon(0.0, 0.5),
                            GeoCoord::from_lat_lon(0.0, 1.0),
                        ],
                    }),
                    properties: HashMap::new(),
                }],
            },
            style,
        );
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        // With three input coords, the midpoint vertices should have
        // colours around 0.5.  Find any vertex with R/G/B in (0.3, 0.7).
        let has_mid = mesh.colors.iter().any(|c| c[0] > 0.3 && c[0] < 0.7);
        assert!(has_mid, "expected midpoint vertices with interpolated colour");
    }

    #[test]
    fn line_gradient_style_roundtrips_through_line_style_layer() {
        use crate::style::{LineStyleLayer, StyleEvalContextFull, line_style_with_state};
        let ramp = blue_to_red_ramp();
        let mut layer = LineStyleLayer::new("grad", "src");
        layer.line_gradient = Some(ramp.clone());
        let state = HashMap::new();
        let ctx = StyleEvalContextFull::new(5.0, &state);
        let vs = line_style_with_state(&layer, &ctx);
        assert!(vs.line_gradient.is_some());
    }

    // -- Fill-pattern tests -----------------------------------------------

    /// Helper: create a tiny 2×2 checkerboard pattern image.
    fn checkerboard_2x2() -> Arc<PatternImage> {
        // RGBA: black, white, white, black
        #[rustfmt::skip]
        let data = vec![
            0, 0, 0, 255,   255, 255, 255, 255,
            255, 255, 255, 255,   0, 0, 0, 255,
        ];
        Arc::new(PatternImage::new(2, 2, data))
    }

    #[test]
    fn pattern_image_validates_data_length() {
        // 2×2 RGBA needs exactly 16 bytes.
        let img = PatternImage::new(2, 2, vec![0u8; 16]);
        assert_eq!(img.width, 2);
        assert_eq!(img.height, 2);
    }

    #[test]
    #[should_panic(expected = "RGBA8 data length")]
    fn pattern_image_rejects_wrong_data_length() {
        let _img = PatternImage::new(2, 2, vec![0u8; 10]);
    }

    #[test]
    fn fill_pattern_generates_uvs() {
        let pattern = checkerboard_2x2();
        let style = VectorStyle::fill_pattern(pattern);

        let geom = Geometry::Polygon(square_polygon());
        let features = FeatureCollection {
            features: vec![Feature {
                geometry: geom,
                properties: HashMap::new(),
            }],
        };
        let layer = VectorLayer::new("pat", features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);

        // Pattern is present → UVs must be generated.
        assert!(mesh.fill_pattern.is_some());
        assert!(
            !mesh.fill_pattern_uvs.is_empty(),
            "expected fill_pattern_uvs to be non-empty"
        );
        // Fill UVs are generated for fill polygon vertices only (not outline
        // stroke vertices), so the count may be less than positions.len()
        // when the style includes an outline.
        assert!(
            mesh.fill_pattern_uvs.len() <= mesh.positions.len(),
            "fill_pattern_uvs should not exceed positions count"
        );
    }

    #[test]
    fn solid_fill_has_no_pattern_uvs() {
        let style = VectorStyle::fill([0.5, 0.5, 0.5, 1.0], [0.0, 0.0, 0.0, 1.0], 1.0);

        let geom = Geometry::Polygon(square_polygon());
        let features = FeatureCollection {
            features: vec![Feature {
                geometry: geom,
                properties: HashMap::new(),
            }],
        };
        let layer = VectorLayer::new("solid", features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);

        assert!(mesh.fill_pattern.is_none());
        assert!(
            mesh.fill_pattern_uvs.is_empty(),
            "solid fills should not generate pattern UVs"
        );
    }

    #[test]
    fn fill_pattern_style_roundtrips_through_fill_style_layer() {
        use crate::style::{FillStyleLayer, StyleEvalContextFull, fill_style_with_state};
        let pattern = checkerboard_2x2();
        let mut layer = FillStyleLayer::new("fp", "src");
        layer.fill_pattern = Some(pattern.clone());
        let state = HashMap::new();
        let ctx = StyleEvalContextFull::new(5.0, &state);
        let vs = fill_style_with_state(&layer, &ctx);
        assert!(vs.fill_pattern.is_some());
        assert_eq!(vs.fill_pattern.as_ref().unwrap().width, 2);
    }

    // -----------------------------------------------------------------------
    // Line-pattern tests
    // -----------------------------------------------------------------------

    fn line_feature() -> FeatureCollection {
        FeatureCollection {
            features: vec![Feature {
                geometry: Geometry::LineString(LineString {
                    coords: vec![
                        GeoCoord::from_lat_lon(0.0, 0.0),
                        GeoCoord::from_lat_lon(0.0, 1.0),
                    ],
                }),
                properties: HashMap::new(),
            }],
        }
    }

    #[test]
    fn line_pattern_generates_uvs() {
        let pattern = checkerboard_2x2();
        let style = VectorStyle::line_pattern(4.0, pattern);
        let layer = VectorLayer::new("lp", line_feature(), style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);

        assert!(mesh.line_pattern.is_some(), "pattern image should be carried to mesh");
        assert!(
            !mesh.line_pattern_uvs.is_empty(),
            "expected line_pattern_uvs to be non-empty"
        );
        assert_eq!(
            mesh.line_pattern_uvs.len(),
            mesh.positions.len(),
            "each position should have a corresponding pattern UV"
        );
    }

    #[test]
    fn line_pattern_uvs_have_correct_v_range() {
        let pattern = checkerboard_2x2();
        let style = VectorStyle::line_pattern(4.0, pattern);
        let layer = VectorLayer::new("lp", line_feature(), style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);

        // Body vertices should have V = 0.0 or V = 1.0 (left/right edges).
        // Cap/join vertices should have V = 0.5.
        let has_left = mesh.line_pattern_uvs.iter().any(|uv| (uv[1] - 0.0).abs() < 0.01);
        let has_right = mesh.line_pattern_uvs.iter().any(|uv| (uv[1] - 1.0).abs() < 0.01);
        assert!(has_left, "expected some V=0.0 vertices (left edge)");
        assert!(has_right, "expected some V=1.0 vertices (right edge)");

        // All V values should be in [0, 1].
        for uv in &mesh.line_pattern_uvs {
            assert!(
                uv[1] >= -0.01 && uv[1] <= 1.01,
                "V coordinate {:.3} outside [0, 1]",
                uv[1]
            );
        }
    }

    #[test]
    fn solid_line_has_no_pattern_uvs() {
        let style = VectorStyle::line([1.0, 0.0, 0.0, 1.0], 4.0);
        let layer = VectorLayer::new("solid", line_feature(), style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);

        assert!(mesh.line_pattern.is_none());
        assert!(
            mesh.line_pattern_uvs.is_empty(),
            "solid lines should not generate pattern UVs"
        );
    }

    #[test]
    fn line_pattern_style_constructor() {
        let pattern = checkerboard_2x2();
        let style = VectorStyle::line_pattern(6.0, pattern.clone());
        assert_eq!(style.render_mode, VectorRenderMode::Line);
        assert_eq!(style.stroke_width, 6.0);
        assert!(style.line_pattern.is_some());
        assert_eq!(style.line_pattern.as_ref().unwrap().width, 2);
    }

    #[test]
    fn line_pattern_style_roundtrips_through_line_style_layer() {
        use crate::style::{LineStyleLayer, StyleEvalContextFull, line_style_with_state};
        let pattern = checkerboard_2x2();
        let mut layer = LineStyleLayer::new("lp", "src");
        layer.line_pattern = Some(pattern.clone());
        let state = HashMap::new();
        let ctx = StyleEvalContextFull::new(5.0, &state);
        let vs = line_style_with_state(&layer, &ctx);
        assert!(vs.line_pattern.is_some());
        assert_eq!(vs.line_pattern.as_ref().unwrap().width, 2);
    }

    #[test]
    fn line_pattern_u_increases_along_line() {
        let pattern = checkerboard_2x2();
        let style = VectorStyle::line_pattern(4.0, pattern);

        // Longer line to get more meaningful distance variation.
        let features = FeatureCollection {
            features: vec![Feature {
                geometry: Geometry::LineString(LineString {
                    coords: vec![
                        GeoCoord::from_lat_lon(0.0, 0.0),
                        GeoCoord::from_lat_lon(0.0, 5.0),
                    ],
                }),
                properties: HashMap::new(),
            }],
        };
        let layer = VectorLayer::new("lp", features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);

        // Body vertices (V=0 or V=1) should have increasing U along the line.
        let body_us: Vec<f32> = mesh
            .line_pattern_uvs
            .iter()
            .filter(|uv| (uv[1] - 0.0).abs() < 0.01 || (uv[1] - 1.0).abs() < 0.01)
            .map(|uv| uv[0])
            .collect();
        assert!(!body_us.is_empty(), "should have body vertices with pattern UVs");
        // The max U should be greater than 0 (line has non-zero length).
        let max_u = body_us.iter().cloned().fold(0.0_f32, f32::max);
        assert!(max_u > 0.0, "max U along line should be > 0, got {max_u}");
    }

    #[test]
    fn heatmap_tessellation_populates_heatmap_points() {
        let gc = |lat: f64, lon: f64| rustial_math::GeoCoord::from_lat_lon(lat, lon);
        let features = FeatureCollection {
            features: vec![Feature {
                geometry: Geometry::Point(Point { coord: gc(0.0, 0.0) }),
                properties: HashMap::new(),
            }],
        };
        let style = VectorStyle::heatmap([1.0, 0.0, 0.0, 1.0], 20.0, 1.0);
        let layer = VectorLayer::new("hm", features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert!(
            !mesh.heatmap_points.is_empty(),
            "heatmap tessellation should populate heatmap_points"
        );
        let pt = &mesh.heatmap_points[0];
        assert!(pt[3] > 0.0, "heatmap radius should be positive: {}", pt[3]);
    }

    #[test]
    fn circle_tessellation_populates_circle_instances() {
        let gc = |lat: f64, lon: f64| rustial_math::GeoCoord::from_lat_lon(lat, lon);
        let features = FeatureCollection {
            features: vec![Feature {
                geometry: Geometry::Point(Point { coord: gc(0.0, 0.0) }),
                properties: HashMap::new(),
            }],
        };
        let style = VectorStyle::circle([0.0, 1.0, 0.0, 1.0], 10.0, [0.0, 0.0, 0.0, 1.0], 2.0);
        let layer = VectorLayer::new("cc", features, style);
        let mesh = layer.tessellate(CameraProjection::WebMercator);
        assert!(
            !mesh.circle_instances.is_empty(),
            "circle tessellation should populate circle_instances"
        );
        assert!(
            mesh.circle_instances[0].radius > 0.0,
            "circle radius should be positive"
        );
    }
}