edde746
a6cca37174
On Linux the Home page, a library's Recommended tab and movie/show detail pages could not be scrolled at all, while Browse, Collections, Playlists, search, downloads and settings scrolled normally. Those three screens are exactly the ones whose viewport is covered by horizontal hub rows. A wheel, trackball, trackpoint or button-scroll event expresses one-axis intent, but the host reports both axes in the same event: on Linux only touchpad-sourced scrolling becomes a pan/zoom sequence that resolves in the gesture arena, and everything else arrives as one PointerScrollEvent carrying whatever dx the device produced. A Scrollable claims a scroll signal as soon as the delta along its own axis is non-zero, and the deepest claimant wins the PointerSignalResolver, so a tenth of a pixel of dx handed the whole event to the horizontal row and the page behind it never moved. Collapse a scroll signal onto its dominant axis in the binding, before hit testing - the last point where the delta can still be corrected, because a Scrollable has already registered with the resolver by the time it sees the event. Pan/zoom events are left alone, so trackpad panning keeps both axes, and a horizontal wheel or tilt still scrolls the row it points at. close #2081
69 lines
3.1 KiB
Dart
69 lines
3.1 KiB
Dart
import 'package:flutter/gestures.dart';
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import 'package:flutter/widgets.dart';
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/// Collapses a diagonal scroll signal onto the axis the viewer actually moved.
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///
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/// A wheel, trackpoint, trackball or button-scroll event expresses one-axis
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/// intent, but the host can report both axes in the same event: on Linux only
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/// touchpad-sourced scrolling becomes a pan/zoom sequence (which resolves in the
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/// gesture arena), while wheel/continuous/tilt sources arrive as a single
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/// [PointerScrollEvent] carrying whatever `dx` the device produced. A trackball
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/// or libinput button-scrolling maps pointer motion straight onto both axes, so
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/// `dx` is essentially never zero there.
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///
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/// That matters because [Scrollable] claims a scroll signal as soon as the delta
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/// along *its own* axis is non-zero, and the deepest claimant wins the
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/// [PointerSignalResolver]. One pixel of `dx` therefore hands the whole event to
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/// a horizontal hub row and the page behind it never scrolls — the Home,
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/// library Recommended and media-detail freeze reported in #2081, on exactly the
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/// screens whose viewport is covered by horizontal rows.
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///
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/// Returns [event] unchanged when it is already single-axis, so the common wheel
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/// path allocates nothing.
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PointerScrollEvent lockScrollSignalToDominantAxis(PointerScrollEvent event) {
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final Offset delta = event.scrollDelta;
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if (delta.dx == 0.0 || delta.dy == 0.0) return event;
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// Ties go to the vertical axis: pages scroll vertically, rows are the nested
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// exception, so an ambiguous event should reach the page.
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final Offset dominant = delta.dx.abs() > delta.dy.abs() ? Offset(delta.dx, 0.0) : Offset(0.0, delta.dy);
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return PointerScrollEvent(
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viewId: event.viewId,
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timeStamp: event.timeStamp,
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kind: event.kind,
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device: event.device,
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position: event.position,
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scrollDelta: dominant,
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embedderId: event.embedderId,
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onRespond: event.respond,
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);
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}
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/// Applies [lockScrollSignalToDominantAxis] to every scroll signal before it is
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/// hit-tested, which is the only place the delta can still be corrected: by the
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/// time a [Scrollable] sees the event it has already registered with the
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/// [PointerSignalResolver], and only the first (deepest) registration runs.
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///
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/// Pan/zoom events are left alone — trackpad panning is resolved by the gesture
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/// arena, which already prefers the axis the viewer moved along.
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mixin PointerScrollAxisLock on GestureBinding {
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@override
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void handlePointerEvent(PointerEvent event) {
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super.handlePointerEvent(event is PointerScrollEvent ? lockScrollSignalToDominantAxis(event) : event);
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}
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}
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/// The app's binding, which exists solely to install [PointerScrollAxisLock].
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class PlezyWidgetsBinding extends WidgetsFlutterBinding with PointerScrollAxisLock {
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static bool _initialized = false;
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/// Creates the binding on first call and returns it afterwards, mirroring
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/// [WidgetsFlutterBinding.ensureInitialized].
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static WidgetsBinding ensureInitialized() {
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if (!_initialized) {
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PlezyWidgetsBinding();
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_initialized = true;
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}
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return WidgetsBinding.instance;
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}
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}
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