Chrome Compositor Architecture: LayerTreeHost and LayerTreeHostImpl

What this episode covers

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.

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