cc::LayerTreeHostImpl (Input Handler & Scroll Logic)
Blink28623 Syys 2025

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 scroll state of all scroll nodes (via the ScrollTree) and determines when a scroll has hit the extent of an element. Currently, this is where overscroll is detected and reported – but only for the root/viewport. For example, the InputHandler sets did_overscroll_root in the scroll result when the root scroll node reaches its boundary , triggering the elastic effect on the root. To support elastic overscroll on non-root elements, this logic in LayerTreeHostImpl (and its ScrollTree/ScrollNode handling) needs to be generalized: it must detect overscroll on any scrollable node and initiate the overscroll animation (via the helper/controller) for that node instead of chaining upward. Understanding LayerTreeHostImpl and how it yields overscroll information (e.g. populating InputHandlerScrollResult.unused_scroll_delta, accumulated overscroll, and overscroll_behavior flags ) is key, as changes here will route overscroll into the ElasticOverscrollController for the right element rather than exclusively the root.

Jaksot(391)

7 Blink View Transition Discovery and UA Stylesheet Generation

7 Blink View Transition Discovery and UA Stylesheet Generation

This document details how the Blink rendering engine manages the technical lifecycle of View Transitions by coordinating DOM updates with visual animations. Once a developer triggers a transition, the...

27 Tammi 31min

6 Blink and Compositor Handshake in View Transitions

6 Blink and Compositor Handshake in View Transitions

The provided text explains the technical handshake between the Blink rendering engine and the compositor during a web view transition. To ensure visual continuity, the system captures a snapshot of th...

27 Tammi 30min

Evolution of CSS: Working Group Drafts and Processes

Evolution of CSS: Working Group Drafts and Processes

The provided text outlines the operations and standardizing procedures of the W3C CSS Working Group, which manages the evolution of web presentation through a modular specification system. It details ...

27 Tammi 38min

5 View Transition Mechanics: Pre-paint and Snapshot Coordination

5 View Transition Mechanics: Pre-paint and Snapshot Coordination

The provided text explains how the Blink rendering engine manages view transitions by utilizing a stable coordinate space known as the snapshot root. This mechanism ensures that animations remain cons...

27 Tammi 27min

4 Blink View Transition Pseudo-Element Tree and Layout Integration

4 Blink View Transition Pseudo-Element Tree and Layout Integration

The provided text explains how the Blink rendering engine manages View Transitions by generating a temporary pseudo-element subtree to represent page changes. This system acts as an overlay, capturing...

26 Tammi 39min

GEM Modern CSS Scroll Positioning and Visibility Specifications

GEM Modern CSS Scroll Positioning and Visibility Specifications

These sources detail the CSS and DOM specifications that govern how elements are positioned and animated when moved into a user's visible area. The documentation introduces scroll-padding and scroll-m...

25 Tammi 33min

[GENERAL] Modern CSS Scroll Positioning and Visibility Specifications

[GENERAL] Modern CSS Scroll Positioning and Visibility Specifications

These sources collectively define the technical standards for how web browsers handle scrolling and element visibility. The documentation details the CSSOM View Module's specific algorithm for the scr...

25 Tammi 30min

Modern CSS Scroll Positioning and Visibility Specifications

Modern CSS Scroll Positioning and Visibility Specifications

These sources collectively define the technical standards for scroll-into-view behavior within modern CSS specifications, covering how elements are positioned and animated when navigated to or targete...

25 Tammi 38min