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🐛 Fix stacked backdrop blurs

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Alonso Torres 2026-06-17 17:44:40 +02:00 committed by GitHub
parent 2defd5c155
commit 0afa108804
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GPG Key ID: B5690EEEBB952194
1 changed files with 22 additions and 7 deletions
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29
render-wasm/src/render.rs
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@ -679,7 +679,6 @@ impl RenderState {
None => return,
};
let target_surface_snapshot = self.surfaces.snapshot(target_surface);
let translation = self
.surfaces
.get_render_context_translation(self.render_area, scale);
@ -726,17 +725,33 @@ impl RenderState {
}
}
// Reset matrix so snapshot draws pixel-for-pixel on the surface.
// Clips survive reset_matrix (stored in device coords).
// Reset matrix so the blur is applied in device space (sigma is already
// scaled by the zoom). Clips survive reset_matrix (stored in device coords).
canvas.reset_matrix();
// Use Src blend to replace content within the clip with the
// blurred version (not SrcOver which would double-render).
// Apply the blur as a backdrop filter on a save_layer. A backdrop filter
// samples the *current device* contents (respecting the active clip),
// which includes whatever has been drawn so far — including any in-flight
// ancestor save_layer, such as a parent frame with opacity < 100% or a
// non-default blend mode. This way the background blur reflects the actual
// pixels behind the shape regardless of the layer stack. Src blend makes
// the layer replace the clipped region with the blurred backdrop instead
// of compositing over it (which would double-render the backdrop).
let mut paint = skia::Paint::default();
paint.set_image_filter(blur_filter);
paint.set_blend_mode(skia::BlendMode::Src);
canvas.draw_image(&target_surface_snapshot, (0, 0), Some(&paint));
let layer_rec = skia::canvas::SaveLayerRec::default()
.backdrop(&blur_filter)
.backdrop_tile_mode(skia::TileMode::Clamp)
.paint(&paint);
canvas.save_layer(&layer_rec);
// Two restores are required, balancing two separate pushes:
// 1. this restore pops the save_layer above; it is the step that composites
// the blurred-backdrop layer back onto the canvas (with the Src paint),
// so it is what actually produces the blurred output.
// 2. the final restore pops the canvas.save() above, removing the shape clip
// and the scale/translate/transform so they don't leak into later drawing.
canvas.restore();
canvas.restore();
}