teksilo_core/widget/

paint_context.rs

// SPDX-License-Identifier: MPL-2.0
// SPDX-FileCopyrightText: 2026 FernTech

use teksilo_canvas::{Rect, Size};

use crate::arena::WidgetArena;
use crate::widget_id::WidgetId;

/// Context available during painting.
pub struct PaintContext<'a> {
    pub theme: &'a crate::styles::Theme,
    /// Accumulated (quantized) scale of the transform scopes enclosing
    /// this widget — `1.0` outside any scale transform, the zoom-derived
    /// raster ladder value inside a `SceneView` / `Scale` wrapper. This
    /// is the ambient text raster scale the walker has already set on
    /// the shared `TextBackend`; widgets normally don't need it (text
    /// drawn via `Canvas::draw_text` / `draw_paragraph` picks it up
    /// automatically), but resolution-dependent custom paint can read
    /// it to densify its own raster content. NOT the HiDPI device scale
    /// — that lives on the renderer/text-service.
    pub scale_factor: f32,
    /// Combined user×OS text-scale factor (`1.0` = 100 %) — the *logical*
    /// accessibility magnification, distinct from the raster `scale_factor`
    /// above. Widgets that paint text via `Theme.typography` already scale
    /// through the effective theme; this is for paint paths that size text
    /// from another source (e.g. a scene `TextItem` that opts in). `1.0` when
    /// no scale is active.
    pub text_scale: f32,
    /// Active layout direction. Used by widgets that have to resolve
    /// Leading/Trailing semantics into geometric Left/Right at paint
    /// time (e.g. attached-side shadow suppression on a popover that
    /// opened off the trailing edge of its anchor).
    pub layout_direction: crate::environment::LayoutDirection,
    /// Whether the widget being painted is effectively enabled —
    /// `false` iff this node or any ancestor has its arena-level
    /// `enabled_state` resolved to `false`. Computed once per node by
    /// the paint walker (start `true` at root, AND with each node's
    /// `enabled_state` value as the walker descends).
    ///
    /// Leaf widgets that paint role-derived colors
    /// ([`crate::color_prop::ColorProp::TextRole`] and the dynamic
    /// variants) consult this to substitute `TextRole::Disabled`
    /// automatically — the single hook that makes any descendant of a
    /// disabled subtree dim without the composite parent doing
    /// per-color bookkeeping. Static and bound color props are not
    /// substituted (caller's literal wins).
    pub effective_enabled: bool,
    // Fed by `teksilo-platform`'s `AccessibilityPreferences::query()` (winit
    // exposes none of these, so the platform crate asks the OS directly) via
    // `WidgetTree::set_accessibility_preferences`; `prefers_large_text` is
    // derived from the OS text-scale factor being greater than 1.0.
    pub prefers_high_contrast: bool,
    pub prefers_reduced_motion: bool,
    pub prefers_large_text: bool,
    /// Whether the host window is currently active (`focused AND not
    /// occluded`). Widgets that change appearance when the window loses focus
    /// read this directly in `paint()` — the selection band in
    /// `TableView`/`TreeTableView` desaturates, text engines swap their
    /// selection colour, custom paint can dim. A window-active flip triggers a
    /// global repaint ([`WidgetArena::mark_all_needs_paint_only`]), so no
    /// per-widget signal binding is required to keep a paint-time read correct.
    /// `true` in headless test contexts.
    pub window_active: bool,
    /// The accumulated clip rectangle this widget is painted within — the
    /// intersection of every `clips_children` ancestor's bounds (a `ScrollArea`
    /// viewport, a `MaxSize`, …), in the same screen space as the widget's own
    /// `bounds`. `None` when no ancestor clips (the widget can paint anywhere).
    ///
    /// The paint walker already computes this to skip fully-offscreen subtrees;
    /// surfacing it lets a widget that is laid out larger than its visible slot
    /// — an editor at full document height inside an outer `ScrollArea`
    /// ("dubious mode") — window its own expensive work to `clip ∩ bounds`
    /// instead of processing the whole document. Correct under arbitrary
    /// nesting, since it is the intersection of *all* clipping ancestors.
    pub clip_bounds: Option<Rect>,
}

impl PaintContext<'_> {
    /// Emit `painter` a second time inside a transform-and-clip scope.
    ///
    /// The mechanism behind the touch magnifier (see
    /// [`crate::text_touch::magnifier`]): `RenderFrame` is a display list, so
    /// content can be drawn again under a different transform instead of being
    /// read back from a framebuffer. `clip` is in the same space as the
    /// widget's own `bounds`; `transform` is composed **beneath** whatever
    /// scope encloses the caller, so a replay inside a scene's view transform
    /// still lands where that scene puts it.
    ///
    /// Three things this deliberately is not:
    ///
    /// * It is not `&mut self`. `Widget::paint` receives a shared
    ///   `&PaintContext`, so a replay a widget could not call from its own
    ///   paint would be useless.
    /// * The clip is a **rectangle**. The renderer realises `SetClip` as a
    ///   scissor rectangle and the pipeline has no path clip or mask pass, so a
    ///   rounded lens is painted as a rounded frame over a rectangular clip —
    ///   see [`crate::text_touch::magnifier`] for what shows in the corners.
    /// * It does not check `painter`. The closure is re-entered during the same
    ///   frame; whether that is safe is the caller's contract, stated at the
    ///   call site in [`crate::text_touch::magnifier`].
    pub fn replay(
        &self,
        canvas: &mut teksilo_canvas::Canvas,
        painter: &dyn Fn(&mut teksilo_canvas::Canvas, &PaintContext<'_>),
        transform: teksilo_canvas::Transform2D,
        clip: Rect,
    ) {
        canvas.save();
        // Clip first, transform second: the renderer maps a clip rect through
        // the transform stack as it stands when the command is emitted, so
        // emitting it before the magnification keeps the lens fixed on screen
        // instead of being magnified along with its contents.
        canvas.set_clip(clip);
        canvas.apply_transform(transform);
        painter(canvas, self);
        canvas.clear_clip();
        canvas.restore();
    }
}

/// Read-only view of the widget tree's geometry passed to
/// [`Widget::after_paint`](super::Widget::after_paint). Wraps a borrow of
/// the arena so a parent widget can read the layout-resolved bounds of
/// any descendant (typically by ids it memoised during `build`) once
/// their paint pass has committed.
///
/// The view exposes only immutable queries; constructing one is
/// crate-internal so the contract stays narrow.
pub struct WidgetTreeView<'a> {
    arena: &'a WidgetArena,
    /// Screen rects of every interactive (non-fading) overlay this
    /// frame — see [`overlay_rects`](Self::overlay_rects).
    overlay_rects: &'a [Rect],
}

impl<'a> WidgetTreeView<'a> {
    pub(crate) fn new(arena: &'a WidgetArena, overlay_rects: &'a [Rect]) -> Self {
        Self {
            arena,
            overlay_rects,
        }
    }

    /// Logical-pixel bounds of `id` after the most recent layout pass.
    /// Returns `Rect::ZERO` for unknown ids.
    pub fn bounds(&self, id: WidgetId) -> Rect {
        self.arena.bounds(id)
    }

    /// Direct arena children of `id`, in order.
    pub fn children(&self, id: WidgetId) -> &[WidgetId] {
        self.arena.children(id)
    }

    /// Whether `id` is a gesture dead-zone boundary — see
    /// [`WidgetNode::gesture_dead_zone`](crate::arena::WidgetNode::gesture_dead_zone)
    /// and the `DeadZone` wrapper widget. Lets a parent classify its own
    /// subtree from `after_paint`: `TitleBar` uses it to carve interactive
    /// controls out of the OS caption region it publishes.
    pub fn is_gesture_dead_zone(&self, id: WidgetId) -> bool {
        self.arena
            .get(id)
            .map(|n| n.gesture_dead_zone)
            .unwrap_or(false)
    }

    /// Whether `id` is active — i.e. not parked dormant by a `Switcher` or a
    /// `visible_when` gate. A dormant node's [`bounds`](Self::bounds) are
    /// stale, so callers walking a subtree must skip it.
    pub fn is_active(&self, id: WidgetId) -> bool {
        self.arena.is_active(id)
    }

    /// Screen rects of every overlay that is interactive this frame —
    /// open and not fading out, the predicate the overlay manager's own
    /// pointer routing uses. Overlay content floats *above* the widget
    /// that anchors it, so an aggregator publishing geometry to the OS
    /// must treat these rects as covering its own: `TitleBar` subtracts
    /// them from the caption it publishes, or a revealed hamburger
    /// `MenuBar` (any overlay over the title bar) would hit-test as
    /// `HTCAPTION` on Windows and the OS would swallow its clicks as a
    /// window drag.
    pub fn overlay_rects(&self) -> &[Rect] {
        self.overlay_rects
    }
}

/// Placement of a child widget during layout.
///
/// `#[non_exhaustive]`: a parent reads and writes the fields of the slice it is
/// handed, and never builds one — so the attribute costs a `place_children`
/// implementation nothing, and it is what makes the next field addition a
/// non-event rather than the breaking change `dormant` was. Use
/// [`WidgetPlacement::new`] where one genuinely has to be constructed.
#[derive(Debug, Clone, Copy)]
#[non_exhaustive]
pub struct WidgetPlacement {
    pub id: WidgetId,
    pub origin: teksilo_canvas::Point,
    pub size: Size,
    /// Park this child dormant for as long as the flag stays set.
    ///
    /// **Only read for a parent whose [`Widget::culls_children`](crate::widget::Widget::culls_children) returns
    /// `true`**, and only such a parent is handed its dormant children here at
    /// all — every other widget still sees its active children and nothing
    /// else, so setting this without opting in does nothing.
    ///
    /// A dormant child leaves paint, the layout recursion, the accessibility
    /// tree and the Tab ring, and keeps every piece of its state — focus,
    /// text, animations — for when it comes back. Clearing the flag wakes it
    /// in the same pass, so a container that culls by viewport shows no hole
    /// on the frame a camera jumps.
    ///
    /// Arrives pre-set to the child's current state, so a parent that ignores
    /// the field changes nothing.
    ///
    /// This is a heavier decision than collapsing `size` to zero, and the two
    /// are worth layering rather than merging: zero size costs the child its
    /// geometry, dormancy costs it its existence. Parking what the user is
    /// interacting with clears focus and cancels pointers — see
    /// [`LayoutContext::for_each_interaction_ancestor`](crate::widget::LayoutContext::for_each_interaction_ancestor).
    pub dormant: bool,
}

impl WidgetPlacement {
    /// A placement at `origin` sized `size`, awake.
    ///
    /// The framework fills the slice a parent is handed; this is for the cases
    /// that stand outside a layout pass — a test driving `place_children`
    /// directly, or a widget assembling placements of its own.
    pub fn new(id: WidgetId, origin: teksilo_canvas::Point, size: Size) -> Self {
        Self {
            id,
            origin,
            size,
            dormant: false,
        }
    }
}