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Test Info:

<!DOCTYPE html>
<html class="reftest-wait reftest-no-flush">
<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
<!--
A test for a partial pre-rendered transform animation moves to a place where
the partial pre-rendered area is completely out of the viewport but still
there remains some amount of area of the entire transform element.
If we mis-recognize it as NOT a jank, checkerboading will happen.
-->
<style>
html {
overflow: hidden;
}
body {
margin: 0px;
padding: 0px;
}
@keyframes anim {
/* translate to a position the partial pre-rendered area is outside of the */
/* viewport but still there should remain visible area. */
to { transform: translateX(-150vw); }
}
#target {
width: 200vw;
height: 200vh;
position: absolute;
transform: translateX(0vw);
}
</style>
<div id="target">
<!--
Put an SVG element so that the transform display item has a blob on
WebRender which means this test properly fails without the proper fix.
-->
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16">
<rect fill="green" width="16" height="16"></rect>
</svg>
</div>
<script>
document.addEventListener("MozReftestInvalidate", () => {
target.style.animation = "anim 100s 1s step-start";
target.addEventListener("animationstart", () => {
// animtionstart event is fired just before requestAnimationFrame callbacks,
// so we need to wait two rAF to make sure the initial animation value is
// composited on the compositor.
requestAnimationFrame(() => {
requestAnimationFrame(() => {
document.documentElement.classList.remove("reftest-wait");
});
});
});
}, { once: true });
</script>
</html>