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Bug 1922904 - Fix bug 1780701 in a different approach. r=botond

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In bug 1780701, we changed ScrollSnapUtils::GetSnapPointForDestination not to
return a valid SnapDestination if the snap position is equal to the original
scroll destination. But it has a bad side-effect on wheel scrolling.

While wheel scrolling, there are multiple wheel inputs comming from OS, in every
wheel input we do use the destination of the animation running at that moment
[1].  So if in the first wheel input we created a smooth animation for snapping
to the SnapDestination, and then in the second wheel input
GetSnapPointForDestination doesn't return any valid SnapDestination so that the
smooth animation is clobbered [2].

To avoid this bad side-effect, we do skip scroll snapping in the call site,
ScrollContainerFrame::ScrollSnap, if the snap position equals to the original
scroll destination.

[1] https://searchfox.org/mozilla-central/rev/53e8dfd81c32f1ab275516406ec06a68136aaef0/gfx/layers/apz/src/AsyncPanZoomController.cpp#2585-2586
[2] https://searchfox.org/mozilla-central/rev/53e8dfd81c32f1ab275516406ec06a68136aaef0/gfx/layers/apz/src/AsyncPanZoomController.cpp#2603

Differential Revision: https://phabricator.services.mozilla.com/D227409
This commit is contained in:
Hiroyuki Ikezoe
2024-11-02 06:37:14 +00:00
parent 9ca48497fc
commit e38ad9d39d
6 changed files with 143 additions and 16 deletions
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7
layout/generic/ScrollContainerFrame.cpp
View File

@@ -5024,6 +5024,13 @@ void ScrollContainerFrame::ScrollSnap(const nsPoint& aDestination,
// site using `GetScrollPosition()` as |aStartPos|.
if (auto snapDestination = GetSnapPointForDestination(
ScrollUnit::DEVICE_PIXELS, snapFlags, pos, destination)) {
// Bail out if there's no scroll position change to do a workaround for bug
// 1665932 (even if the __layout__ scroll position is unchanged, the
// corresponding scroll offset update will change the __visual__ scroll
// offset in APZ).
if (snapDestination->mPosition == destination) {
return;
}
destination = snapDestination->mPosition;
ScrollToWithOrigin(
destination, nullptr /* range */,