As per the CSS Animations spec [1], animations must behave as if 'will-change'
is specified, and as per the Will Change spec [2] the element having
'will-change' property other than 'auto' behaves as a containing block for
fixed-pos descendants. This reftest tests that behavior. The reason we also
specified visibility:hidden there is that we are going to optimize transform
animations on/inside visibility:hidden element, so this reftest also tests it.
In this reftest, if the containing block is correctly generated, the fixed-pos
element is rendered inside the parent element, thus the scrollable element
overflows, then the vertial scroll bar appears.
[1] https://drafts.csswg.org/css-animations-1/#animations
> While an animation is applied but has not finished, or has finished but has
> an animation-fill-mode of forwards or both, the user agent must act as if
> the will-change property ([css-will-change-1]) on the element additionally
> includes all the properties animated by the animation.
[2] https://drafts.csswg.org/css-will-change/#will-change
> If any non-initial value of a property would cause the element to generate
> a containing block for fixed positioned elements, specifying that property
> in will-change must cause the element to generate a containing block for
> fixed positioned elements.
MozReview-Commit-ID: Kx5Fdx8FJUG
--HG--
extra : rebase_source : 926f10590e90a10876339ccbea331a981f9f4773
As per the CSS Animations spec [1], animations must behave as if 'will-change'
is specified, and as per the Will Change spec [2] the element having
'will-change' property other than 'auto' behaves as a containing block for
fixed-pos descendants. This reftest tests that behavior. The reason we also
specified visibility:hidden there is that we are going to optimize transform
animations on/inside visibility:hidden element, so this reftest also tests it.
In this reftest, if the containing block is correctly generated, the fixed-pos
element is rendered inside the parent element, thus the scrollable element
overflows, then the vertial scroll bar appears.
[1] https://drafts.csswg.org/css-animations-1/#animations
> While an animation is applied but has not finished, or has finished but has
> an animation-fill-mode of forwards or both, the user agent must act as if
> the will-change property ([css-will-change-1]) on the element additionally
> includes all the properties animated by the animation.
[2] https://drafts.csswg.org/css-will-change/#will-change
> If any non-initial value of a property would cause the element to generate
> a containing block for fixed positioned elements, specifying that property
> in will-change must cause the element to generate a containing block for
> fixed positioned elements.
MozReview-Commit-ID: Kx5Fdx8FJUG
--HG--
extra : rebase_source : 926f10590e90a10876339ccbea331a981f9f4773
Hiroyuki Ikezoe
Margareta Eliza Balazs