Architecture and Value Tracking of Chromium Paint Worklets

The provided sources describe the Chromium compositor’s architecture for animating CSS PaintWorklets and native properties off the main thread. This technical pipeline relies on PropertyKey to uniquely identify an animating dependency by its element ID and property name, while PropertyValue serves as a lightweight container for transporting updated numeric or color values. Centered in this process is the AnimatedPaintWorkletTracker, a specialized cache that monitors value changes, tracks layer dependencies, and manages a "two-slot" diffing engine to identify when a property has mutated. Rather than forcing a repaint on every animation tick, the system delegates the final decision to specific PaintWorkletInput subtypes, which evaluate whether a value transition is visually significant enough to invalidate the cached record. This design efficiently bridges Blink’s style engine and the CC compositor, allowing for smooth, high-performance animations of custom and native paint properties without constant main-thread intervention. The documentation also highlights a functional split where JavaScript-based worklets receive direct value overrides while native worklets interpret float progress values to reconstruct visual results.