Architectural Guide to the Blink PaintLayer System
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The Blink PaintLayer system serves as a specialized infrastructure within the Chromium rendering engine designed to manage complex visual tasks like stacking, clipping, and compositing. Instead of creating a layer for every element, Blink selectively generates PaintLayers based on specific triggers such as CSS transforms, opacity, or positioning. These layers form a tree structure that often diverges from the standard DOM to reflect the actual painting order and Z-index requirements of a webpage. The system distinguishes between self-painting layers, which manage their own stacking contexts, and non-self-painting layers used primarily for technical bookkeeping like overflow clipping. By integrating with paint property trees and the LayoutNG fragment system, PaintLayers ensure that visual effects are applied correctly even when elements are split across multiple columns or pages. Ultimately, this architecture facilitates GPU acceleration by identifying which layers should be promoted to GraphicsLayers for more efficient compositing.
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