Layer Invalidation to Partial Swap
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The source details Chromium's damage tracking architecture, a critical mechanism within the cc compositor that identifies regions of the screen requiring redrawing to ensure rendering efficiency. This system distinguishes between content changes signaled by the renderer, known as paint invalidation, and internal compositor-driven updates, such as tile replacements, which generate damage rects. Changes propagate through the layer hierarchy via DamageTracker objects associated with RenderSurfaces, which carefully map localized layer modifications and property shifts (like transforms) into cumulative damage on the render target. In Chromium’s multi-process environment, the Viz SurfaceAggregator integrates damage rectangles from independently submitted child frames (SurfaceLayers) into a single, cohesive output. The final comprehensive damage rectangle is delivered with the CompositorFrame, enabling the graphics system to perform partial swaps and minimize buffer updates, thereby optimizing performance and power consumption. The architecture achieves efficiency by aggressively reusing unchanged resources, like previously rendered tiles and cached RenderPasses.
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