Blink Compositor Promotion of CSS Animations

The technical sources provide an extensive analysis of how the Blink rendering engine (used in Chromium/Chrome) determines whether a CSS animation can be executed on the compositor thread instead of the main thread to improve performance and achieve smooth frame rates. This process involves a complex pipeline, beginning with style calculation and proceeding through layout and layer assignment, where an element must be assigned a composited layer and corresponding property tree nodes to be eligible for acceleration. The critical decision is made by the function CheckCanStartAnimationOnCompositor(), which only permits animations on a limited set of properties—primarily transform, opacity, filter, and backdrop-filter—while rejecting anything affecting layout or requiring frame-by-frame repainting. If accelerated, the animation’s keyframes are converted into CompositorAnimation objects and run by the GPU-assisted compositor, allowing the main thread to remain free for other tasks.