cranpose_ui/

renderer.rs

use crate::layout::{LayoutBox, LayoutNodeData, LayoutTree};
use crate::modifier::{DrawCommand as ModifierDrawCommand, Point, Rect, Size};
use crate::widgets::LayoutNode;
use cranpose_core::{MemoryApplier, NodeId};
use cranpose_ui_graphics::DrawPrimitive;

/// Layer that a paint operation targets within the rendering pipeline.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum PaintLayer {
    Behind,
    Content,
    Overlay,
}

/// A rendered operation emitted by the headless renderer stub.
#[derive(Clone, Debug, PartialEq)]
pub enum RenderOp {
    Primitive {
        node_id: NodeId,
        layer: PaintLayer,
        primitive: DrawPrimitive,
    },
    Text {
        node_id: NodeId,
        rect: Rect,
        value: String,
    },
}

/// A collection of render operations for a composed scene.
#[derive(Clone, Debug, Default, PartialEq)]
pub struct RecordedRenderScene {
    operations: Vec<RenderOp>,
}

impl RecordedRenderScene {
    pub fn new(operations: Vec<RenderOp>) -> Self {
        Self { operations }
    }

    /// Returns a slice of recorded render operations in submission order.
    pub fn operations(&self) -> &[RenderOp] {
        &self.operations
    }

    /// Consumes the scene and yields the owned operations.
    pub fn into_operations(self) -> Vec<RenderOp> {
        self.operations
    }

    /// Returns an iterator over primitives that target the provided paint layer.
    pub fn primitives_for(&self, layer: PaintLayer) -> impl Iterator<Item = &DrawPrimitive> {
        self.operations.iter().filter_map(move |op| match op {
            RenderOp::Primitive {
                layer: op_layer,
                primitive,
                ..
            } if *op_layer == layer => Some(primitive),
            _ => None,
        })
    }
}

/// A lightweight renderer that walks the layout tree and materialises paint commands.
#[derive(Default)]
pub struct HeadlessRenderer;

impl HeadlessRenderer {
    pub fn new() -> Self {
        Self
    }

    pub fn render(&self, tree: &LayoutTree) -> RecordedRenderScene {
        let mut operations = Vec::new();
        self.render_box(tree.root(), &mut operations);
        RecordedRenderScene::new(operations)
    }

    #[allow(clippy::only_used_in_recursion)]
    fn render_box(&self, layout: &LayoutBox, operations: &mut Vec<RenderOp>) {
        let rect = layout.rect;
        let (mut behind, mut overlay) = evaluate_modifier(layout.node_id, &layout.node_data, rect);

        operations.append(&mut behind);

        // Render text content if present in modifier slices.
        // This follows Jetpack Compose's pattern where text is a modifier node capability
        // (TextModifierNode implements LayoutModifierNode + DrawModifierNode + SemanticsNode)
        if let Some(text) = layout.node_data.modifier_slices().text_content() {
            operations.push(RenderOp::Text {
                node_id: layout.node_id,
                rect,
                value: text.to_string(),
            });
        }

        // Render children
        for child in &layout.children {
            self.render_box(child, operations);
        }

        operations.append(&mut overlay);
    }
}

fn evaluate_modifier(
    node_id: NodeId,
    data: &LayoutNodeData,
    rect: Rect,
) -> (Vec<RenderOp>, Vec<RenderOp>) {
    let mut behind = Vec::new();
    let mut overlay = Vec::new();

    let size = Size {
        width: rect.width,
        height: rect.height,
    };

    // Render via modifier slices - all drawing now goes through draw commands
    // collected from the modifier node chain, including backgrounds, borders, etc.
    for command in data.modifier_slices().draw_commands() {
        match command {
            ModifierDrawCommand::Behind(func) => {
                for primitive in func(size) {
                    behind.push(RenderOp::Primitive {
                        node_id,
                        layer: PaintLayer::Behind,
                        primitive: translate_primitive(primitive, rect.x, rect.y),
                    });
                }
            }
            ModifierDrawCommand::Overlay(func) => {
                for primitive in func(size) {
                    overlay.push(RenderOp::Primitive {
                        node_id,
                        layer: PaintLayer::Overlay,
                        primitive: translate_primitive(primitive, rect.x, rect.y),
                    });
                }
            }
        }
    }

    (behind, overlay)
}

fn translate_primitive(primitive: DrawPrimitive, dx: f32, dy: f32) -> DrawPrimitive {
    match primitive {
        DrawPrimitive::Rect { rect, brush } => DrawPrimitive::Rect {
            rect: rect.translate(dx, dy),
            brush,
        },
        DrawPrimitive::RoundRect { rect, brush, radii } => DrawPrimitive::RoundRect {
            rect: rect.translate(dx, dy),
            brush,
            radii,
        },
    }
}

// ═══════════════════════════════════════════════════════════════════════════
// Direct Applier Rendering (new architecture)
// ═══════════════════════════════════════════════════════════════════════════

impl HeadlessRenderer {
    /// Renders the scene by traversing LayoutNodes directly via the Applier.
    /// This is the new architecture that eliminates per-frame LayoutTree reconstruction.
    pub fn render_from_applier(
        &self,
        applier: &mut MemoryApplier,
        root: NodeId,
    ) -> RecordedRenderScene {
        let mut operations = Vec::new();
        self.render_node_from_applier(applier, root, Point::default(), &mut operations);
        RecordedRenderScene::new(operations)
    }

    #[allow(clippy::only_used_in_recursion)]
    fn render_node_from_applier(
        &self,
        applier: &mut MemoryApplier,
        node_id: NodeId,
        parent_offset: Point,
        operations: &mut Vec<RenderOp>,
    ) {
        // Read layout state and node data from LayoutNode
        let node_data = match applier.with_node::<LayoutNode, _>(node_id, |node| {
            let state = node.layout_state();
            let modifier_slices = node.modifier_slices_snapshot();
            let children: Vec<NodeId> = node.children.iter().copied().collect();
            (state, modifier_slices, children)
        }) {
            Ok(data) => data,
            Err(_) => return, // Node not found or type mismatch
        };

        let (layout_state, modifier_slices, children) = node_data;

        // Skip nodes that weren't placed
        if !layout_state.is_placed {
            return;
        }

        // Calculate absolute position
        let abs_x = parent_offset.x + layout_state.position.x;
        let abs_y = parent_offset.y + layout_state.position.y;

        let rect = Rect {
            x: abs_x,
            y: abs_y,
            width: layout_state.size.width,
            height: layout_state.size.height,
        };

        let size = Size {
            width: rect.width,
            height: rect.height,
        };

        // Collect draw commands from modifier slices
        let mut behind = Vec::new();
        let mut overlay = Vec::new();

        for command in modifier_slices.draw_commands() {
            match command {
                ModifierDrawCommand::Behind(func) => {
                    for primitive in func(size) {
                        behind.push(RenderOp::Primitive {
                            node_id,
                            layer: PaintLayer::Behind,
                            primitive: translate_primitive(primitive, rect.x, rect.y),
                        });
                    }
                }
                ModifierDrawCommand::Overlay(func) => {
                    for primitive in func(size) {
                        overlay.push(RenderOp::Primitive {
                            node_id,
                            layer: PaintLayer::Overlay,
                            primitive: translate_primitive(primitive, rect.x, rect.y),
                        });
                    }
                }
            }
        }

        operations.append(&mut behind);

        // Render text content if present
        if let Some(text) = modifier_slices.text_content() {
            operations.push(RenderOp::Text {
                node_id,
                rect,
                value: text.to_string(),
            });
        }

        // Calculate content offset for children (includes node position + content_offset from padding etc.)
        let child_offset = Point {
            x: abs_x + layout_state.content_offset.x,
            y: abs_y + layout_state.content_offset.y,
        };

        // Render children
        for child_id in children {
            self.render_node_from_applier(applier, child_id, child_offset, operations);
        }

        operations.append(&mut overlay);
    }
}

#[cfg(test)]
#[path = "tests/renderer_tests.rs"]
mod tests;