cc Transform and Scroll Trees
Blink28628 Syys 2025

cc Transform and Scroll Trees

The source text details the architecture of Chromium's compositor, focusing on the tandem operation of two critical data structures: the Transform Tree and the Scroll Tree. The Transform Tree manages visual coordinate space transformations, including CSS transforms and scroll offsets, with each TransformNode calculating its final position relative to its parent using local matrices and the scroll translation. In parallel, the Scroll Tree, composed of ScrollNodes, handles the logical state of scrollable elements, defining constraints like scrollable bounds, allowed directions, and scroll chaining behavior. Crucially, the sources explain that the two trees are linked via a shared ElementId and that while the Scroll Tree determines how a scroll should happen (bounds and policy), the Transform Tree executes the change by holding and applying the live scroll_offset to visually move the layer content, enabling smooth, composite-threaded scrolling.

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