Chromium LayerContext Deep Dive: RenderingNG and Scroll Updates

The source material, primarily an excerpt from a 2025 technical report, provides an in-depth analysis of the LayerContext abstraction within the Chromium RenderingNG pipeline, specifically when the browser's compositor and the GPU's display compositor run in separate processes using the "Trees In Viz" configuration. LayerContext acts as the crucial boundary object, with the VizLayerContext implementation on the client side responsible for serializing incremental updates—including property tree changes, layer properties, and scroll offsets—into Mojo messages. Conversely, the LayerContextImpl on the server (GPU) side receives these messages, applies the updates to its local LayerTreeHostImpl, and then draws and submits the final frame. This mechanism is central to ensuring efficient synchronization of scroll deltas and other state changes across process boundaries without requiring a full commit for every update.