Bug 1430884 - A reftest that transform animation makes the element as a containing block for fixed-pos descendants even if the element is visibility:hidden and if the animating value is 'transform:none'. r?birtles
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
new file mode 100644
--- /dev/null
+++ b/layout/reftests/css-animations/containing-block-on-visibility-hidden-ref.html
@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<style>
+#parent {
+ visibility: hidden;
+ will-change: transform;
+}
+
+#fixed {
+ position: fixed;
+ background-color: green;
+ height: 100px;
+ width: 100px;
+}
+
+#scroll {
+ overflow-y: scroll;
+ overflow-x: hidden;
+ height: 80px;
+ width: 100px;
+}
+</style>
+<div id="scroll">
+ <div id="parent">
+ <div id="fixed"></div>
+ </div>
+</div>
new file mode 100644
--- /dev/null
+++ b/layout/reftests/css-animations/containing-block-on-visibility-hidden.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<title>
+Transform animation generates a containing block for fixed-pos descendants
+even if the animation value is 'transform:none'
+</title>
+<style>
+#parent {
+ visibility: hidden;
+ animation: anim 100s step-end;
+}
+
+#fixed {
+ position: fixed;
+ background-color: green;
+ height: 100px;
+ width: 100px;
+}
+
+#scroll {
+ overflow-y: scroll;
+ overflow-x: hidden;
+ height: 80px;
+ width: 100px;
+}
+@keyframes anim {
+ 0% { transform: none; }
+ 100% { transform: translateX(0px); }
+}
+</style>
+<div id="scroll">
+ <div id="parent">
+ <div id="fixed"></div>
+ </div>
+</div>
--- a/layout/reftests/css-animations/reftest.list
+++ b/layout/reftests/css-animations/reftest.list
@@ -65,8 +65,9 @@ fails-if(layerChecksEnabled) == backgrou
== no-style-sharing-with-animations.html no-style-sharing-with-animations-ref.html
== continuation-opacity.html continuation-opacity-ref.html
== ib-split-sibling-opacity.html about:blank
== opacity-animation-in-fixed-opacity-parent.html opacity-animation-in-fixed-opacity-parent-ref.html
== opacity-animation-in-delay.html about:blank
== transform-animation-in-delay.html transform-animation-in-delay-ref.html
+== containing-block-on-visibility-hidden.html containing-block-on-visibility-hidden-ref.html
