The sources provide a detailed technical explanation of the PaintArtifactCompositor (PAC), a fundamental component of Chrome's modern Blink rendering pipeline known as CompositeAfterPaint (CAP). The PAC’s primary role is to serve as a bridge between the painting phase and the GPU compositing phase, consuming the rendered drawing commands (PaintArtifact) and converting them into an efficient structure of GPU layers and property trees. This process, called layerization, involves merging or separating PaintChunks based on compositing reasons and performance heuristics to minimize overhead while ensuring visual correctness and enabling smooth, off-main-thread scrolling and animations. The documentation also covers the PAC’s lifecycle, debugging tools, and its historical evolution as part of the larger RenderingNG architectural change.
