зеркало из https://github.com/mozilla/gecko-dev.git
54a0194045
This patch does basically throttle animations on visibility:hidden element
and unthrottle it once the animating element became visible or a child of the
animating element became visible. But still there are some cases that we don't
throttle such animations perfectly. For example;
div.style.visibility = 'hidden'; // the 'div' has no children at this moment
div.animate(..);
// The animation is throttled
div.appendChild(visibleChild);
// The animation isn't throttled
visibleChild.style.visibility = 'hidden';
// Now the animation should be throttled again, but actually it's not.
To throttle this case properly, when the |visibleChild|'s visibility changed
to hidden, we would need to do either
1) Check all siblings of the |visibleChild| have no visible children
or
2) The parent element stores visible children count somewhere and decrease it
and check whether the count is zero
To achieve 1) we need to walk up ancestors and their siblings, actually it's
inefficient.
2) is somewhat similar to what we already do for animating images but it's hard
to reuse it for CSS animations since it does not take into account that
descendants' visibilities.
Another example that this patch does not optimize is the the case where
animating element has children whose visibility is inherited and the element
itself initially visible something like this;
let child = document.createElement('div'); // child visibility is 'inherit'
div.appendChild(child);
div.animate(..); // the 'div' is visible
// The animation isn't throttled since the animating element is visible
div.style.visiblily = 'hidden';
// Now the animation should be throttled, but it's not since this patch does
// not descend down all descendants to check they are invisible or not when the
// animating element visibility changed to hidden.
This patch adds a test case for this case introduced with todo_is().
Another test case added in this patch fails if we don't use
nsPlaceholderFrame::GetRealFrameFor() in HasNoVisibleDescendants().
MozReview-Commit-ID: BJwzQvP9Yc4
--HG--
extra : rebase_source : e56505706bb2799b59bbfb3bbcce4a9ce86892f4
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