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Fix stale terminal viewport synchronization #10

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Merged
bharathm03 merged 1 commit into from
Sep 1, 2026
Merged

Fix stale terminal viewport synchronization #10

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50 changes: 45 additions & 5 deletions pkgs/vte/ghostty_vte_flutter/lib/src/terminal_view.dart
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -489,6 +489,15 @@ class _GhosttyTerminalViewState extends State<GhosttyTerminalView> {
/// Latest offset-from-bottom awaiting a single post-frame engine drive.
int? _pendingEngineOffset;

/// Latest engine offset awaiting a post-frame Flutter scroll-layer sync.
/// A null value also cancels an already scheduled callback when a newer
/// local scroll takes ownership of the viewport.
int? _pendingFlutterOffset;

/// Prevents an engine-originated [ScrollController.jumpTo] from being sent
/// straight back to the engine as a new user scroll.
bool _isSyncingFlutterViewport = false;

/// True while the view is synchronously driving the engine viewport in
/// response to its OWN scroll. `scrollViewportToOffsetFromBottom` notifies
/// listeners (`_markDirty`), which re-enters `_onControllerChanged`; without
Expand Down Expand Up @@ -852,6 +861,8 @@ class _GhosttyTerminalViewState extends State<GhosttyTerminalView> {
void didUpdateWidget(covariant GhosttyTerminalView oldWidget) {
super.didUpdateWidget(oldWidget);
if (oldWidget.controller != widget.controller) {
_pendingEngineOffset = null;
_pendingFlutterOffset = null;
oldWidget.controller.removeListener(_onControllerChanged);
widget.controller.addListener(_onControllerChanged);
_lastReportedCols = -1;
Expand Down Expand Up @@ -966,6 +977,11 @@ class _GhosttyTerminalViewState extends State<GhosttyTerminalView> {
/// scrollbar is authoritative because column changes can reflow rows and
/// alter the offset-from-bottom even when the user did not scroll.
void _syncScrollOffsetFromEngine() {
// A local scroll has already been accepted but has not reached the engine
// yet. Its newer intent wins over notifications emitted in the meantime.
if (_pendingEngineOffset != null) {
return;
}
final bar = widget.controller.viewportScrollbar;
if (bar == null) {
return;
Expand All @@ -978,16 +994,28 @@ class _GhosttyTerminalViewState extends State<GhosttyTerminalView> {
if (!_scrollController.hasClients || _lastMeasuredLinePixels <= 0) {
return;
}
final alreadyScheduled = _pendingFlutterOffset != null;
_pendingFlutterOffset = next;
if (alreadyScheduled) {
return;
}
WidgetsBinding.instance.addPostFrameCallback((_) {
if (!mounted || !_scrollController.hasClients) {
final target = _pendingFlutterOffset;
_pendingFlutterOffset = null;
if (!mounted || target == null || !_scrollController.hasClients) {
return;
}
final clamped = (next * _lastMeasuredLinePixels).clamp(
final clamped = (target * _lastMeasuredLinePixels).clamp(
0.0,
_scrollController.position.maxScrollExtent,
);
if ((_scrollController.offset - clamped).abs() >= 0.5) {
_scrollController.jumpTo(clamped);
_isSyncingFlutterViewport = true;
try {
_scrollController.jumpTo(clamped);
} finally {
_isSyncingFlutterViewport = false;
}
}
});
}
Expand All @@ -996,6 +1024,11 @@ class _GhosttyTerminalViewState extends State<GhosttyTerminalView> {
if (!mounted || _lastMeasuredLinePixels <= 0) {
return;
}
if (!_isSyncingFlutterViewport) {
// Invalidate an older engine-to-Flutter callback before it can move the
// scroll layer back underneath this newer local scroll.
_pendingFlutterOffset = null;
}
final nextOffsetLines = (_scrollController.offset / _lastMeasuredLinePixels)
.round();
if (nextOffsetLines == _scrollOffsetLines) {
Expand All @@ -1004,7 +1037,9 @@ class _GhosttyTerminalViewState extends State<GhosttyTerminalView> {
setState(() {
_scrollOffsetLines = nextOffsetLines;
});
_driveEngineViewport(nextOffsetLines);
if (!_isSyncingFlutterViewport) {
_driveEngineViewport(nextOffsetLines);
}
}

bool _resetScrollOffsetToBottom() {
Expand Down Expand Up @@ -3220,6 +3255,7 @@ class _GhosttyTerminalViewState extends State<GhosttyTerminalView> {
_TerminalMetrics metrics, {
_TerminalSelectionGranularity granularity =
_TerminalSelectionGranularity.line,
bool autoScrollWhileHeld = false,
}) {
// See `_beginSelection`: a slow pinch can sit inside long-press slop long
// enough for the recognizer to fire — swallow it while the pinch is live.
Expand Down Expand Up @@ -3264,7 +3300,9 @@ class _GhosttyTerminalViewState extends State<GhosttyTerminalView> {
fallbackLocalPosition: localPosition,
);
}
_syncAutoScroll(localPosition, size, metrics);
if (autoScrollWhileHeld) {
_syncAutoScroll(localPosition, size, metrics);
}
}

Widget _buildPointerGestureLayer({
Expand All @@ -3288,6 +3326,7 @@ class _GhosttyTerminalViewState extends State<GhosttyTerminalView> {
size,
metrics,
granularity: _TerminalSelectionGranularity.visualRow,
autoScrollWhileHeld: true,
);
},
onLongPressMoveUpdate: (details) =>
Expand Down Expand Up @@ -3341,6 +3380,7 @@ class _GhosttyTerminalViewState extends State<GhosttyTerminalView> {
size,
metrics,
granularity: _TerminalSelectionGranularity.visualRow,
autoScrollWhileHeld: true,
);
} else {
_beginLineSelection(details.localPosition, size, metrics);
Expand Down
92 changes: 86 additions & 6 deletions pkgs/vte/ghostty_vte_flutter/test/terminal_view_test.dart
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1689,7 +1689,8 @@ void main() {
await tester.tapAt(firstRowTarget);
await tester.pumpAndSettle();

expect(currentContent?.text, 'Line 0');
expect(currentContent, isNotNull);
final liveBottomRowText = currentContent?.text;

final scrollbar = await tester.startGesture(const Offset(595, 48));
await scrollbar.moveTo(const Offset(595, 320));
Expand All @@ -1704,7 +1705,7 @@ void main() {
await tester.pumpAndSettle();

expect(currentContent, isNotNull);
expect(currentContent?.text, isNot('Line 0'));
expect(currentContent?.text, isNot(liveBottomRowText));
});

testWidgets(
Expand Down Expand Up @@ -1783,7 +1784,8 @@ void main() {
await tester.pump(const Duration(milliseconds: 40));
await tester.tapAt(firstRowTarget);
await tester.pumpAndSettle();
expect(currentContent?.text, 'Line 0');
expect(currentContent, isNotNull);
final liveBottomRowText = currentContent?.text;

scrollController.jumpTo(300);
await tester.pumpAndSettle();
Expand All @@ -1796,7 +1798,78 @@ void main() {
await tester.pumpAndSettle();

expect(currentContent, isNotNull);
expect(currentContent?.text, isNot('Line 0'));
expect(currentContent?.text, isNot(liveBottomRowText));
});

testWidgets('completed desktop triple-click does not keep auto-scrolling', (
tester,
) async {
if (!hasNativeTerminal) {
return;
}

final scrollController = ScrollController();
addTearDown(scrollController.dispose);
controller.appendDebugOutput(
List<String>.generate(120, (index) => 'Line $index').join('\r\n'),
);

await tester.pumpWidget(
buildView(
showHeader: false,
autofocus: true,
scrollController: scrollController,
),
);
await tester.pumpAndSettle();

scrollController.jumpTo(300);
await tester.pumpAndSettle();
final before = controller.viewportScrollbar!;
final beforeOffsetFromBottom =
before.total - before.length - before.offset;

const firstRowTarget = Offset(30, 24);
await tester.tapAt(firstRowTarget);
await tester.pump(const Duration(milliseconds: 40));
await tester.tapAt(firstRowTarget);
await tester.pump(const Duration(milliseconds: 40));
await tester.tapAt(firstRowTarget);
await tester.pumpAndSettle();

final after = controller.viewportScrollbar!;
expect(after.total - after.length - after.offset, beforeOffsetFromBottom);
expect(scrollController.offset, 300);
});

testWidgets('new output cannot overwrite a pending local viewport scroll', (
tester,
) async {
if (!hasNativeTerminal) {
return;
}

final scrollController = ScrollController();
addTearDown(scrollController.dispose);
controller.appendDebugOutput(
List<String>.generate(120, (index) => 'Line $index').join('\r\n'),
);

await tester.pumpWidget(
buildView(showHeader: false, scrollController: scrollController),
);
await tester.pumpAndSettle();

final observedOffsets = <double>[];
scrollController.addListener(
() => observedOffsets.add(scrollController.offset),
);
scrollController.jumpTo(300);
controller.appendDebugOutput('\r\nTail');
await tester.pumpAndSettle();

expect(observedOffsets, isNot(contains(0.0)));
expect(scrollController.offset, 300);
});

testWidgets('a trackpad two-finger scroll drives a program holding the '
Expand Down Expand Up @@ -2006,8 +2079,15 @@ void main() {
controller.appendDebugOutput('\r\nTail');
await tester.pumpAndSettle();

// Without auto-follow the viewport stays put.
expect(scrollController.offset, preservedOffset);
// Without auto-follow the same transcript row stays visible. Since the
// Flutter scroll layer measures from the live bottom, its coordinate
// grows when a new row is appended below that held viewport.
final bar = controller.viewportScrollbar!;
final expectedOffset =
(bar.total - bar.length - bar.offset) *
_measureTestMetrics().linePixels;
expect(scrollController.offset, expectedOffset);
expect(scrollController.offset, greaterThan(preservedOffset));

// The rendered first row must still show the same content as before the
// new output arrived — the viewport did not move.
Expand Down
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