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use rosace_core::types::{Point, Rect, Size};
use rosace_layout::Constraints;
use rosace_render::PictureRecorder;
use rosace_state::Atom;
use super::{Widget, LayoutCtx, PaintCtx, TransformLayerEntry};
/// Captures a child widget into an independent Picture and applies a 2D scroll
/// offset on the GPU without re-rendering the child (D080, Phase 17/19).
///
/// Phase 17: CPU shift in paint() — UV offset uniform wired in compositor.
/// Phase 19: child is recorded into a separate PictureRecorder and pushed into
/// PaintCtx.transform_entries (D087) for the platform to replay into its own
/// SkiaCanvas and present as an extra GPU compositor layer (D088).
pub struct TransformLayer<W: Widget + Send + Sync + 'static> {
pub child: W,
/// Scroll offset in **logical** pixels, positive = scroll down.
pub scroll_y: Atom<f32>,
/// Horizontal scroll offset in logical pixels.
pub scroll_x: Atom<f32>,
/// Viewport height in logical pixels — content beyond this is clipped.
pub viewport_h: f32,
}
/// Physical-pixel cap for TransformLayer content (D082).
pub const MAX_TRANSFORM_DIM: u32 = 4096;
impl<W: Widget + Send + Sync + 'static> TransformLayer<W> {
pub fn new(child: W, viewport_h: f32, scroll_y: Atom<f32>) -> Self {
Self {
child,
scroll_y,
scroll_x: rosace_state::use_atom(0.0_f32),
viewport_h,
}
}
}
impl<W: Widget + Send + Sync + 'static> Widget for TransformLayer<W> {
fn layout(&self, ctx: &LayoutCtx) -> Size {
// Viewport size is what we occupy in the parent layout.
let unconstrained = Constraints::loose(ctx.constraints.max_width_f32(), f32::INFINITY);
let child_lctx = LayoutCtx::new(unconstrained, ctx.font, ctx.theme);
let child_size = self.child.layout(&child_lctx);
Size {
width: child_size.width,
height: self.viewport_h.min(child_size.height),
}
}
fn paint(&self, ctx: &mut PaintCtx) {
let scroll_y = self.scroll_y.get();
let scroll_x = self.scroll_x.get();
let vp_rect = ctx.rect;
// Measure child with unconstrained height to get its natural size.
let child_lctx = ctx.layout_ctx(Constraints::loose(vp_rect.size.width, f32::INFINITY));
let child_size = self.child.layout(&child_lctx);
// Record child into a SEPARATE PictureRecorder (D087).
// The child is painted at (0,0) — the platform positions it on screen.
let mut sub_rec = PictureRecorder::new();
let child_origin = Point { x: 0.0, y: 0.0 };
let child_rect = Rect { origin: child_origin, size: child_size };
let sub_node = ctx.tree.borrow_mut().slot(ctx.node, true);
let mut sub_ctx = PaintCtx {
recorder: &mut sub_rec,
rect: child_rect,
font: ctx.font,
theme: ctx.theme.clone(),
tree: ctx.tree.clone(),
node: sub_node,
owner: ctx.owner,
clip_rect: None,
};
self.child.paint(&mut sub_ctx);
let picture = sub_rec.finish();
// Attach the entry to this node — the platform replays it into a
// dedicated canvas (D088); it persists across clean frames (D091).
ctx.attach_transform(TransformLayerEntry {
picture,
child_size,
viewport_rect: vp_rect,
zoom: 1.0,
scroll_x,
scroll_y,
});
// Register wheel scrolling straight into the non-reactive offset
// channel, keyed by this node id (D090). A scroll tick updates the
// channel + requests a present-only frame — it dirties NO component,
// so the content texture is reused and only the compositor UV offset
// changes. Zero CPU paint on scroll.
let node_id = ctx.node as u64;
let max_x = (child_size.width - vp_rect.size.width).max(0.0);
let max_y = (child_size.height - self.viewport_h).max(0.0);
ctx.register_scroll_target(
vp_rect,
super::render_tree::ScrollAxes::BOTH,
std::sync::Arc::new(move |dx, dy| {
rosace_state::scroll_offset_by(node_id, -dx, -dy, max_x, max_y);
}),
);
// Update ctx.rect to the viewport size for sibling layout correctness.
ctx.rect = Rect {
origin: vp_rect.origin,
size: Size {
width: vp_rect.size.width,
height: self.viewport_h.min(vp_rect.size.height),
},
};
}
}