Chrome Compositor Architecture: LayerTreeHost and LayerTreeHostImpl
Blink2863 Okt 2025

Chrome Compositor Architecture: LayerTreeHost and LayerTreeHostImpl

The sources provide an extensive architectural overview of the Chrome cc compositor module, focusing on the collaboration between three critical classes: LayerTreeHost (LTH), LayerTreeHostImpl (LTHI), and LayerTreeHostClient. The LTH resides on the main thread, acting as the public API that receives content updates from the embedder (like Blink) and initiates the frame pipeline. The LTHI runs on the dedicated compositor thread, handling crucial tasks such as rasterization, impl-side animations, and input processing, ultimately producing a CompositorFrame for the Viz display compositor. Finally, the LayerTreeHostClient is an interface implemented by the renderer (or UI) that allows the compositor to drive frame updates (e.g., BeginMainFrame) and receive feedback about commit and presentation timing, ensuring thread synchronization is managed primarily through the blocking Commit Phase and the Activation Phase.



Episoder(397)

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 Okt 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 Okt 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 Okt 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 Okt 202547min

blink::PrePaintTreeWalk

blink::PrePaintTreeWalk

cross‑frame pre‑paint traversal. Runs in the InPrePaint lifecycle phase. Walks the entire layout tree starting at the root LocalFrameView, updating paint invalidation state and computing the context n...

10 Okt 202531min

blink::NGPhysicalFragment and friends

blink::NGPhysicalFragment and friends

Layout takes the styled DOM and produces a fragment tree of positioned boxes. In modern Blink this is LayoutNG; the core artifact is NGPhysicalFragment, which stores geometry and is used downstream fo...

10 Okt 202537min

blink::StyleEngine

blink::StyleEngine

style invalidation & resolution (recalc). 
Given DOM/style changes since the last frame, StyleEngine computes updated ComputedStyles, manages active stylesheets/media query state, and marks the right ...

10 Okt 202534min

blink::Document & blink::DocumentLifecycle

blink::Document & blink::DocumentLifecycle

states that gate phases. The document owns the DOM and keeps a DocumentLifecycle state machine that ensures we do things in phase order (style before layout, pre‑paint before paint, etc.). Lifecycle t...

10 Okt 202535min

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