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F11 — Scroll fidelity ​

A notched wheel click, a trackpad fling with momentum, and a high-resolution wheel are three different signals that frameworks routinely flatten into one lossy number. This demo logs the raw scroll stream per device class.

Requirements ​

  1. Log every scroll event with its full native payload, from both a notched wheel and a trackpad (where present):
    • Wayland: wl_pointer.axis value + axis_v120 (120ths) + axis_source (wheel/finger/continuous) + axis_stop + frame grouping (wl_pointer.frame).
    • X11: legacy buttons 4/5/6/7 AND XInput2 smooth scrolling (XI_Motion valuators with XIScrollClass) — log both representations of the same physical scroll.
    • Win32: WM_MOUSEWHEEL/WM_MOUSEHWHEEL raw wheelDelta, demonstrating correct accumulation of sub-120 deltas (precision touchpads send fractions of WHEEL_DELTA) until a line-scroll threshold; log SPI_GETWHEELSCROLLLINES.
    • macOS: scrollWheel: with scrollingDeltaX/Y, hasPreciseScrollingDeltas, phases (phase/momentumPhase began/changed/ended) through a full fling.
  2. Render a scrollable ruler so over/under-scroll bugs are visible; print per-gesture totals.
  3. Capture one identical physical gesture on both device classes and diff the event streams.

Instrumentation ​

scroll axis=v|h value=… v120=… source=… phase=… (fields as available per platform), scroll_stop, gesture summary lines.

Findings to record ​

  • Per platform: the smallest representable scroll step, how device class is distinguished, and how momentum is delivered (events vs app-synthesized).
  • The Win32 accumulation contract (what breaks if you truncate instead of accumulate).
  • The X11 dual representation and its double-event trap (core + XI2 for one scroll).
  • What a lossless framework scroll event must carry.

Verification ​

Wheel halves: Wayland/X11 Tier A with synthetic wheel input (xdotool click 4/5; weston test clients). Trackpad halves (momentum, phases, fractional deltas) need real hardware: Tier C on the Mac trackpad and a Windows precision touchpad. A[wine] covers Win32 message plumbing only.