Compositor-Thread Scrolling – CC Mechanics and Property Trees
Blink28611 Marras 2025

Compositor-Thread Scrolling – CC Mechanics and Property Trees

The source provides an extensive technical overview of Chrome’s Compositor-Thread Scrolling architecture, explaining how modern web rendering achieves smooth, low-latency scrolling by handling most scroll events off the main thread. This process relies on key data structures called property trees—specifically the ScrollTree, TransformTree, and ClipTree—which manage scroll offsets, geometric transformations, and viewport boundaries, respectively. The LayerTreeHostImpl orchestrates the sequence: it receives input events via the InputHandlerProxy, determines the scroll target via hit testing, updates the ScrollNode's offset, and leverages the TransformTree to translate content on the GPU without needing the main thread for layout or style updates. Additionally, the system details how it manages advanced features like scroll animations (flings), scroll snapping, platform-specific overscroll effects (elasticity/glow), and fallbacks to main-thread scrolling when necessary, ensuring the continuous flow of rendered frames.


Jaksot(417)

blink::PropertyTreeManager

blink::PropertyTreeManager

bridges Blink property trees → cc property trees. Given Blink’s Transform/Clip/Effect/Scroll nodes (from paint property trees), this class creates/updates the cc counterparts (cc::TransformNode, cc::C...

10 Loka 202546min

blink::PaintArtifactCompositor

blink::PaintArtifactCompositor

turns chunks into compositor layers & updates cc property trees. Consumes the new PaintArtifact and does the layerization and property‑tree updates required for compositor draw. It supports fast paths...

10 Loka 202529min

blink::PaintChunk and blink::DisplayItemList

blink::PaintChunk and blink::DisplayItemList

grouping and content. PaintChunk: groups sequential display items that share the same property‑tree state and cull/visibility; it’s the unit we layerize and invalidate.DisplayItemList: the recorded Sk...

10 Loka 202537min

blink::PaintArtifact

blink::PaintArtifact

the immutable “what to draw” package for this frame. A PaintArtifact is the product of Blink painting: a DisplayItemList plus an ordered vector of PaintChunks. It is immutable post‑creation and design...

10 Loka 202531min

blink::PaintController

blink::PaintController

builds the display list + paint chunks and manages caching. As painters call into GraphicsContext, they also drive a PaintController which groups drawing into display items and paint chunks (each keye...

10 Loka 202529min

blink::GraphicsContext

blink::GraphicsContext

immediate drawing API that records to a display list. Painters for layout objects use GraphicsContext to “draw”—but in modern Blink those calls get recorded into a display list (PaintRecord) backed by...

10 Loka 202544min

blink::TransformPaintPropertyNode / ClipPaintPropertyNode / EffectPaintPropertyNode / ScrollPaintPropertyNode

blink::TransformPaintPropertyNode / ClipPaintPropertyNode / EffectPaintPropertyNode / ScrollPaintPropertyNode

These are the nodes within those four trees. Every piece of painted content (a “paint chunk”) is associated with a tuple of (Transform, Clip, Effect, Scroll) nodes—its PropertyTreeState. This precisel...

10 Loka 202533min

blink::PaintPropertyTreeBuilder

blink::PaintPropertyTreeBuilder

builds/updates paint property trees.Consumes the layout/fragment data and produces the four paint property trees (Transform, Clip, Effect, Scroll) for the current frame. These trees encode coordinate ...

10 Loka 202547min