1 files changed, 54 insertions, 0 deletions
diff --git a/layout/reftests/transform/partial-prerender-translate-6.html b/layout/reftests/transform/partial-prerender-translate-6.html
new file mode 100644
index 0000000000..1ec13f44d7
--- /dev/null
+++ b/layout/reftests/transform/partial-prerender-translate-6.html
@@ -0,0 +1,54 @@
+<!DOCTYPE html>
+<html class="reftest-wait reftest-no-flush">
+<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
+<style>
+html {
+  overflow: hidden;
+}
+body {
+  margin: 0px;
+  padding: 0px;
+}
+@keyframes anim {
+  /* The reftest window size is (800x1000), which means the partial prerender */
+  /* area is (1125x900). Thus -325px(= 800 - 1125) is the boundary where jank */
+  /* happens, so we choose a value close to -325px so that within a next      */
+  /* couple of frames jank should happen. */
+  0% { transform: translateX(-324px); }
+  100% { transform: translateX(-2000px); }
+}
+#target {
+  width: 1600px;
+  /* Use a smallar value than the reftest window height to avoid bloating up  */
+  /* svg inside this element beyond the window height */
+  height: 900px;
+  position: absolute;
+  transform: translateX(0px);
+}
+</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 1600 900">
+    <!-- green on the pre-render area -->
+    <rect fill="green" x="0" width="1125" height="900"></rect>
+    <rect fill="red" x="1125" width="875" height="900"></rect>
+  </svg>
+</div>
+<script>
+document.addEventListener("MozReftestInvalidate", () => {
+  // A shorter animation-duration than we normally use (100s) because if we used
+  // the longer duration it may NOT fail this test even if any jank happens.
+  target.style.animation = "anim 10s 1s";
+  target.addEventListener("animationstart", () => {
+    // Wait a second to make sure the animation gets stucked (i.e. jank) at the
+    // boundary (325px).
+    setTimeout(() => {
+      document.documentElement.classList.remove("reftest-wait");
+    }, 1000);
+  });
+}, { once: true });
+</script>
+</html>