Module scroll_state 

Pure scroll state management — the single source of truth for scroll offsets.

Architecture

ScrollManager is the exclusive owner of all scroll state. Other modules interact with scrolling only through its public API:

• Platform shell (macos/events.rs, etc.): Calls record_scroll_from_hit_test() to queue trackpad/mouse wheel input for the physics timer.
• Scroll physics timer (scroll_timer.rs): Consumes inputs via ScrollInputQueue, applies physics, and pushes CallbackChange::ScrollTo for each updated node.
• Event processing (event_v2.rs): Processes ScrollTo changes, sets scroll positions, and checks VirtualView re-invocation transparently.
• Gesture manager (gesture.rs): Tracks drag state and emits AutoScrollDirection — does NOT modify scroll offsets directly.
• Render loop: Calls tick() every frame to advance easing animations.
• WebRender sync (wr_translate2.rs): Reads offsets via get_scroll_states_for_dom() to synchronize scroll frames.
• Layout (cache.rs): Registers scroll nodes via register_or_update_scroll_node() after layout completes.

Scroll Flow

Platform Event Handler
  → record_scroll_from_hit_test() → ScrollInputQueue
  → starts SCROLL_MOMENTUM_TIMER_ID if not running

Timer fires (every ~16ms):
  → queue.take_all() → physics integration
  → push_change(CallbackChange::ScrollTo)

ScrollTo processing (event_v2.rs):
  → scroll_manager.set_scroll_position()
  → virtual_view_manager.check_reinvoke() (transparent VirtualView support)
  → repaint

This module provides:

• Smooth scroll animations with easing
• Event source classification for scroll events
• Scrollbar geometry and hit-testing
• Virtual scroll bounds for VirtualView nodes

Structs

AnimatedScrollState

The complete scroll state for a single node (with animation support)

ScrollAnimation

Details of an in-progress smooth scroll animation.

ScrollInput

A single scroll input event to be processed by the physics timer.

ScrollInputQueue

Thread-safe queue for scroll inputs, shared between event handlers and timer callbacks.

ScrollManager

Manages all scroll state and animations for a window

ScrollNodeInfo

Read-only snapshot of a scroll node’s state, returned by CallbackInfo queries.

ScrollTickResult

Result of a scroll tick, indicating what actions are needed

ScrollbarHit

Result of a scrollbar hit-test

ScrollbarState

Scrollbar geometry state (calculated per frame, used for hit-testing and rendering)

Enums

ScrollInputSource

Classifies the source of a scroll input event.

ScrollbarComponent

Which component of a scrollbar was hit during hit-testing