8000 fix(terminal): make scroll wheel work again in alternate screen by egertaia · Pull Request #42 · amirlehmam/wmux · GitHub
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fix(terminal): make scroll wheel work again in alternate screen #42

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amirlehmam merged 1 commit into from
Jun 20, 2026
Merged

fix(terminal): make scroll wheel work again in alternate screen #42

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74 changes: 65 additions & 9 deletions src/renderer/hooks/useTerminal.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -210,15 +210,71 @@ export function useTerminal({ surfaceId, shell, cwd, visible = true, focused = t
const wheelHost = terminalRef.current;
const WheelEvent) => {
if (ev.deltaY === 0) return;
// Only hijack the wheel for scrollback on the NORMAL buffer. Full-screen
// TUIs (Claude Code, vim, less, htop…) switch to the ALTERNATE buffer
// (DECSET 1049), which has no scrollback — terminal.scrollLines() there is
// a no-op. If we still preventDefault/stopPropagation we also suppress
// xterm's native behavior of forwarding the wheel to the app (mouse-wheel
// reports when mouse tracking is on, otherwise arrow-key sequences), which
// is the ONLY way those apps scroll their own content. So on the alt
// buffer we fall through and let xterm handle it.
if (terminal.buffer.active.type !== 'normal') return;

if (terminal.buffer.active.type !== 'normal') {
// Alternate screen (Claude Code, vim, less, htop…): there is no scrollback
// buffer, so terminal.scrollLines() is a no-op. We must forward wheel events
// to the PTY application ourselves.
//
// xterm's own forwarding (_handleWheel / _handlePassiveWheel) is unreliable
// here because: (a) the wheel listener is only registered when the app has
// explicitly requested wheel mouse events via DECSET; (b) _consumeWheelEvent
// silently returns 0 when render-service cell dimensions are temporarily
// unavailable (e.g. after the WebGL context swap introduced in v0.8.4),
// causing _sendEvent to drop the event with no feedback. Taking ownership
// here avoids both failure modes. (#41 regression from v0.8.4+)
ev.preventDefault();
ev.stopPropagation();
const id = ptyIdRef.current;
if (!id) return;

// Compute scroll count (same heuristic as normal-buffer path).
let amount: number;
if (ev.deltaMode === 1 /* DOM_DELTA_LINE */) {
amount = ev.deltaY;
} else if (ev.deltaMode === 2 /* DOM_DELTA_PAGE */) {
amount = ev.deltaY * (terminal.rows || 24);
} else {
amount = ev.deltaY / 17;
}
const count = Math.sign(amount) * Math.max(1, Math.round(Math.abs(amount)));
if (count === 0) return;

// xterm adds .enable-mouse-events to the screen element when the app has
// enabled any mouse protocol (DECSET 1000/1002/1003). In that case we send
// SGR mouse-wheel sequences (button 64=up, 65=down) which all modern TUIs
// understand. Without mouse tracking we fall back to up/down arrow keys,
// which is what xterm's _handlePassiveWheel does natively.
const hasMouseTracking = !!(terminalRef.current?.querySelector('.enable-mouse-events'));

if (hasMouseTracking) {
// Compute approximate terminal column/row from mouse pixel position so
// apps that care about scroll origin (e.g. split-pane TUIs) work correctly.
const rect = terminalRef.current?.getBoundingClientRect();
const cellW = rect && terminal.cols > 0 ? rect.width / terminal.cols : 0;
const cellH = rect && terminal.rows > 0 ? rect.height / terminal.rows : 0;
const col = rect && cellW > 0
? Math.max(1, Math.min(terminal.cols, Math.ceil((ev.clientX - rect.left) / cellW)))
: Math.ceil(terminal.cols / 2);
const row = rect && cellH > 0
? Math.max(1, Math.min(terminal.rows, Math.ceil((ev.clientY - rect.top) / cellH)))
: Math.ceil(terminal.rows / 2);
const btn = count < 0 ? 64 : 65; // 64 = wheel-up, 65 = wheel-down
const seq = `\x1b[<${btn};${col};${row}M`;
for (let i = 0; i < Math.abs(count); i++) {
window.wmux.pty.write(id, seq);
}
} else {
// No mouse tracking: send arrow keys (up/down) as a line-by-line scroll.
const seq = count < 0 ? '\x1b[A' : '\x1b[B';
for (let i = 0; i < Math.abs(count); i++) {
window.wmux.pty.write(id, seq);
}
}
return;
}

// Normal buffer: scroll wmux's own scrollback.
ev.preventDefault();
ev.stopPropagation();
let amount: number;
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