The source text explains how Chromium handles gesture and scroll events within its input pipeline, particularly focusing on the interaction between the Blink/UI thread and the compositor thread. It details the lifecycle of a scroll sequence, where a GestureScrollBegin/Update/End event drives a corresponding ScrollBegin/Update/End on the compositor, which is responsible for latching a target scroll node and applying scroll offsets. The document emphasizes that scroll sequences are generally non-overlapping on the compositor, meaning only one scroll is active at a time, and a new scroll event must terminate the previous one before starting. A key exception is highlighted: pinch-zoom gestures can overlap concurrently with scroll sequences, as Chromium uses separate state and logic to handle the scaling and panning associated with pinching alongside an ongoing scroll.
