Module scroll_timer 

Scroll physics timer callback — the core of the timer-based scroll architecture.

This module implements the scroll physics as a regular timer callback, using the same transactional push_change(CallbackChange::ScrollTo) pattern as all other state modifications. There is nothing special about the scroll timer — it is a normal user-space timer that happens to be started by the framework.

Architecture

Platform Event Handler
  → ScrollManager.record_scroll_input(ScrollInput)
  → starts SCROLL_MOMENTUM_TIMER if not running

Timer fires (every timer_interval_ms from ScrollPhysics):
  1. queue.take_recent(100) — consume up to 100 most recent inputs
  2. For each input:
     - TrackpadContinuous → set offset directly (OS handles momentum)
     - WheelDiscrete → add impulse to velocity
     - Programmatic → set target position
  3. Integrate physics: velocity decay, clamping
  4. push_change(CallbackChange::ScrollTo) for each updated node
  5. Return continue_and_update() or terminate_unchanged()

Key Design Decisions

• No mutable access to LayoutWindow needed: Uses CallbackChange::ScrollTo (the same transactional pattern as all other callbacks).
• Shared queue via Arc: The ScrollInputQueue is cloned into the timer’s RefAny data. Event handlers push, timer pops.
• Platform-independent: Works on macOS, Windows, Linux — anywhere timers work.
• Self-terminating: When all velocities are below threshold and no inputs pending, the timer returns TerminateTimer::Terminate.

Structs

NodeScrollPhysics

Per-node scroll physics state

ScrollPhysicsState

State stored in the timer’s RefAny data.

Functions

scroll_physics_timer_callback

The scroll physics timer callback.