## TUI2: Normalize Mouse Scroll Input Across Terminals (Wheel +
Trackpad)
This changes TUI2 scrolling to a stream-based model that normalizes
terminal scroll event density into consistent wheel behavior (default:
~3 transcript lines per physical wheel notch) while keeping trackpad
input higher fidelity via fractional accumulation.
Primary code: `codex-rs/tui2/src/tui/scrolling/mouse.rs`
Doc of record (model + probe-derived data):
`codex-rs/tui2/docs/scroll_input_model.md`
### Why
Terminals encode both mouse wheels and trackpads as discrete scroll
up/down events with direction but no magnitude, and they vary widely in
how many raw events they emit per physical wheel notch (commonly 1, 3,
or 9+). Timing alone doesn’t reliably distinguish wheel vs trackpad, so
cadence-based heuristics are unstable across terminals/hardware.
This PR treats scroll input as short *streams* separated by silence or
direction flips, normalizes raw event density into tick-equivalents,
coalesces redraws for dense streams, and exposes explicit config
overrides.
### What Changed
#### Scroll Model (TUI2)
- Stream detection
- Start a stream on the first scroll event.
- End a stream on an idle gap (`STREAM_GAP_MS`) or a direction flip.
- Normalization
- Convert raw events into tick-equivalents using per-terminal
`tui.scroll_events_per_tick`.
- Wheel-like vs trackpad-like behavior
- Wheel-like: fixed “classic” lines per wheel notch; flush immediately
for responsiveness.
- Trackpad-like: fractional accumulation + carry across stream
boundaries; coalesce flushes to ~60Hz to avoid floods and reduce “stop
lag / overshoot”.
- Trackpad divisor is intentionally capped: `min(scroll_events_per_tick,
3)` so terminals with dense wheel ticks (e.g. 9 events per notch) don’t
make trackpads feel artificially slow.
- Auto mode (default)
- Start conservatively as trackpad-like (avoid overshoot).
- Promote to wheel-like if the first tick-worth of events arrives
quickly.
- Fallback for 1-event-per-tick terminals (no tick-completion timing
signal).
#### Trackpad Acceleration
Some terminals produce relatively low vertical event density for
trackpad gestures, which makes large/faster swipes feel sluggish even
when small motions feel correct. To address that, trackpad-like streams
apply a bounded multiplier based on event count:
- `multiplier = clamp(1 + abs(events) / scroll_trackpad_accel_events,
1..scroll_trackpad_accel_max)`
The multiplier is applied to the trackpad stream’s computed line delta
(including carried fractional remainder). Defaults are conservative and
bounded.
#### Config Knobs (TUI2)
All keys live under `[tui]`:
- `scroll_wheel_lines`: lines per physical wheel notch (default: 3).
- `scroll_events_per_tick`: raw vertical scroll events per physical
wheel notch (terminal-specific default; fallback: 3).
- Wheel-like per-event contribution: `scroll_wheel_lines /
scroll_events_per_tick`.
- `scroll_trackpad_lines`: baseline trackpad sensitivity (default: 1).
- Trackpad-like per-event contribution: `scroll_trackpad_lines /
min(scroll_events_per_tick, 3)`.
- `scroll_trackpad_accel_events` / `scroll_trackpad_accel_max`: bounded
trackpad acceleration (defaults: 30 / 3).
- `scroll_mode = auto|wheel|trackpad`: force behavior or use the
heuristic (default: `auto`).
- `scroll_wheel_tick_detect_max_ms`: auto-mode promotion threshold (ms).
- `scroll_wheel_like_max_duration_ms`: auto-mode fallback for
1-event-per-tick terminals (ms).
- `scroll_invert`: invert scroll direction (applies to wheel +
trackpad).
Config docs: `docs/config.md` and field docs in
`codex-rs/core/src/config/types.rs`.
#### App Integration
- The app schedules follow-up ticks to close idle streams (via
`ScrollUpdate::next_tick_in` and `schedule_frame_in`) and finalizes
streams on draw ticks.
- `codex-rs/tui2/src/app.rs`
#### Docs
- Single doc of record describing the model + preserved probe
findings/spec:
- `codex-rs/tui2/docs/scroll_input_model.md`
#### Other (jj-only friendliness)
- `codex-rs/tui2/src/diff_render.rs`: prefer stable cwd-relative paths
when the file is under the cwd even if there’s no `.git`.
### Terminal Defaults
Per-terminal defaults are derived from scroll-probe logs (see doc).
Notable:
- Ghostty currently defaults to `scroll_events_per_tick = 3` even though
logs measured ~9 in one setup. This is a deliberate stopgap; if your
Ghostty build emits ~9 events per wheel notch, set:
```toml
[tui]
scroll_events_per_tick = 9
```
### Testing
- `just fmt`
- `just fix -p codex-core --allow-no-vcs`
- `cargo test -p codex-core --lib` (pass)
- `cargo test -p codex-tui2` (scroll tests pass; remaining failures are
known flaky VT100 color tests in `insert_history`)
### Review Focus
- Stream finalization + frame scheduling in `codex-rs/tui2/src/app.rs`.
- Auto-mode promotion thresholds and the 1-event-per-tick fallback
behavior.
- Trackpad divisor cap (`min(events_per_tick, 3)`) and acceleration
defaults.
- Ghostty default tradeoff (3 vs ~9) and whether we should change it.
Introduce a full codex-tui source snapshot under the new codex-tui2
crate so viewport work can be replayed in isolation.
This change copies the entire codex-rs/tui/src tree into
codex-rs/tui2/src in one atomic step, rather than piecemeal, to keep
future diffs vs the original viewport bookmark easy to reason about.
The goal is for codex-tui2 to render identically to the existing TUI
behind the `features.tui2` flag while we gradually port the
viewport/history commits from the joshka/viewport bookmark onto this
forked tree.
While on this baseline change, we also ran the codex-tui2 snapshot test
suite and accepted all insta snapshots for the new crate, so the
snapshot files now use the codex-tui2 naming scheme and encode the
unmodified legacy TUI behavior. This keeps later viewport commits
focused on intentional behavior changes (and their snapshots) rather
than on mechanical snapshot renames.
Josh McKinney ·