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fix: prefer pointer events over semantics tap for mouse clicks on web - #191529
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This pull request updates the ClickDebouncer in the Flutter Web engine to flush queued pointer events and drop the click event for mouse-generated clicks, allowing mouse gestures to be recognized precisely instead of using SemanticsAction.tap. Corresponding tests have been updated to use touch events, and a regression test has been added. Feedback is provided to add a defensive check in _isDebouncingMouseEvents to prevent a potential StateError when accessing the first element of an empty queue.
| bool get _isDebouncingMouseEvents { | ||
| final List<ui.PointerData>? data = _state?.queue.first.data; | ||
| return data != null && data.isNotEmpty && data.first.kind == ui.PointerDeviceKind.mouse; | ||
| } |
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To prevent potential StateError crashes when accessing .first on an empty queue, it is safer to use defensive programming and check if the queue is null or empty before accessing its elements.
| bool get _isDebouncingMouseEvents { | |
| final List<ui.PointerData>? data = _state?.queue.first.data; | |
| return data != null && data.isNotEmpty && data.first.kind == ui.PointerDeviceKind.mouse; | |
| } | |
| bool get _isDebouncingMouseEvents { | |
| final queue = _state?.queue; | |
| if (queue == null || queue.isEmpty) { | |
| return false; | |
| } | |
| final List<ui.PointerData>? data = queue.first.data; | |
| return data != null && data.isNotEmpty && data.first.kind == ui.PointerDeviceKind.mouse; | |
| } |
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Thanks for working on this, the #188859 problem is real and the patch is nice and small.
One concern before it can land: on Chrome, screen reader activation also produces mouse pointer events. Blink sends pointerdown, pointerup and click with pointerType: 'mouse' at the element center, all in one task. That sequence
now takes the new mouse branch, so the click is dropped and nodes that rely on SemanticsAction.tap, such as Semantics(onTap: ...) with no gesture detector underneath, stop responding.
I verified it with VoiceOver on macOS Chrome:
- Before: https://flutter-demo-82-before.web.app
- After, with this PR: https://flutter-demo-82-after.web.app
Press VO+U, pick "Semantics only button" from the Buttons list, then press VO+Space. The counter goes up on the before app but stays at 0 on the after app.
It would also be great to add a test for the one-task mouse sequence that still expects SemanticsAction.tap.
|
@flutter-zl Good catch, thanks for the repro. Updated the PR so the mouse branch is skipped when |
Chrome turns screen reader activation into mouse pointerdown, pointerup and click events dispatched in one task. Only flush pointer events for mouse clicks once debouncing has started, which happens after the pointerdown's task, so screen reader activation keeps producing SemanticsAction.tap.
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Thanks for the quick update, this looks good to me.
I rebuilt my demos on the new head and verified with VoiceOver on macOS Chrome: activating "Semantics only button" now counts up on https://flutter-demo-82-after.web.app, so screen reader taps on Semantics(onTap: ...) nodes work again. A physical mouse click is flushed as pointer events, matching the behavior with semantics off.
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Roll Flutter from fcfb4f203eae to 934720261be0 (38 revisions) flutter/flutter@fcfb4f2...9347202 2026-11-03 [email protected] Roll Skia from 5bceaa033999 to c733ad3e37cb (5 revisions) (flutter/flutter#195872) 2026-11-03 [email protected] Roll Skia from 34d2bf479385 to 5bceaa033999 (9 revisions) (flutter/flutter#195864) 2026-11-03 [email protected] fix: prefer pointer events over semantics tap for mouse clicks on web (flutter/flutter#191529) 2026-11-03 [email protected] [VPAT] Expose a semantics text field value while it is not being edited (flutter/flutter#195445) 2026-11-03 [email protected] [Impeller] Make a GL context current before constructing an AiksContext without a surface (flutter/flutter#195629) 2026-11-03 [email protected] [flutter_tools] Eliminate globals.dart from project.dart (flutter/flutter#194066) 2026-11-03 [email protected] [tool] Complete context runner elimination and migrate AppContext usages to ToolContext (flutter/flutter#190797) 2026-11-03 [email protected] [web] Unify font collections between CanvasKit and Skwasm (flutter/flutter#195539) 2026-11-03 [email protected] [Android] Replay predictive back state for retained engines (flutter/flutter#192286) 2026-11-03 [email protected] [vulkan]: Adds depth/stencil synchronization for subpasses (flutter/flutter#195689) 2026-11-03 [email protected] [web] Honor requested upscaling in instantiateImageCodecWithSize and ImageDescriptor.instantiateCodec (flutter/flutter#195836) 2026-11-03 [email protected] Roll Skia from 866b61ca92c9 to 34d2bf479385 (9 revisions) (flutter/flutter#195848) 2026-11-03 [email protected] Roll Fuchsia Test Scripts from xl1LWBuppzu-BnOzV... to B6zarykZp6PKWRueg... 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This PR fixes
Tap*Detailsreporting the center of the semantics node andPointerDeviceKind.unknownfor mouse clicks on web when semantics is enabled.When semantics is enabled,
ClickDebouncerwithholds the pointer events that lead up to a DOM "click" on a tappable semantics node and forwards the click as aSemanticsAction.tapinstead. That action carries neither a position nor a device kind, so the framework synthesizes the tap at the center of the semantics node withPointerDeviceKind.unknown. For a merged semantics node that also means the tap is attributed to the merged node rather than to whatever was actually under the cursor.The debouncer exists for assistive technologies, which drive taps either through clicks that come with no pointer events at all, or through touch. Neither of those paths is affected by this change: when the withheld pointer events came from a mouse, they are now flushed to the framework and the click is dropped, so mouse gestures are recognized exactly like they are when semantics is off.
Fixes: #188859
Fixes: #146063
Pre-launch Checklist
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