cc::LayerImpl: Compositor Layer Deep Dive
Blink2861 Marras 2025

cc::LayerImpl: Compositor Layer Deep Dive

The sources provide an exhaustive technical explanation of the cc::LayerImpl class, which is the core representation of a visual element within Chromium's multi-threaded rendering pipeline. These layers exist exclusively on the compositor thread and are created or updated during the commit process from the main thread, operating in a layer list mode that leverages four types of property trees (Transform, Clip, Effect, Scroll) to manage hierarchical relationships and properties instead of traditional parent-child pointers. The layer objects are crucial for the performance optimization of drawing frames, as they store geometry, manage input regions for hit testing, and are instrumental in the asynchronous tiling and rasterization system (especially through PictureLayerImpl) and the three-tree model (Active, Pending, Recycle) used for frame staging and reuse. Ultimately, each layer's state is used in the quad generation step to produce a viz::CompositorFrame for the display compositor.


Jaksot(397)

gpu::SkiaOutputSurfaceImplOnGpu / gpu::CommandBuffer

gpu::SkiaOutputSurfaceImplOnGpu / gpu::CommandBuffer

Bridges Skia’s recorded commands to the GPU command buffer; submits and SwapBuffers to present. (Backend: GL/Vulkan/Metal via GPU process.)

23 Syys 202532min

viz::SkiaRenderer

viz::SkiaRenderer

Renderer that turns quads into Skia operations (recording DDLs / drawing to the output surface).

23 Syys 202552min

viz::Display

viz::Display

The display compositor that walks the aggregated render passes and issues draw commands for the final output.

23 Syys 202538min

cc::LayerTreeHostImpl (Input Handler & Scroll Logic)

cc::LayerTreeHostImpl (Input Handler & Scroll Logic)

Scroll processing and overscroll detection in the compositor. The LayerTreeHostImpl in cc implements the compositor-thread InputHandler that processes gesture scroll updates and flings. It manages the...

23 Syys 202527min

blink::EventHandler (Blink core input handling)

blink::EventHandler (Blink core input handling)

Scroll chain builder and overscroll chaining logic. Blink’s EventHandler is responsible for building the scroll chain (the sequence of nested scrollable ancestors) when the user scrolls an element . I...

23 Syys 202526min

blink::ElasticOverscrollController

blink::ElasticOverscrollController

Overscroll orchestration and animation. This Blink-side controller manages the rubber-banding (elastic stretch and rebound) effect when a scrollable area is overscrolled. It observes gesture scroll ev...

23 Syys 202526min

viz::Surface / SurfaceAggregator

viz::Surface / SurfaceAggregator

Receives frames from one or more surfaces (main page and OOPIFs), aggregates them into a single display frame.

23 Syys 202535min

viz::CompositorFrameSink (client side)

viz::CompositorFrameSink (client side)

The submission interface used by cc to hand the frame to viz.

23 Syys 202531min