Fix DCHECK when compositing additive CSS transform animations

Previously CSSTransformNonInterpolableValue assumed that anything that was composited on-top of would be single. However that is not true; in the simple case where there is a replace animation before it, the replace effect will be a pair: target.animate({ transform: [ 'scale(1)', 'scale(2)' ] }, 1000); target.animate({ transform: [ 'rotate(0)', 'rotate(90deg)' ] }, { duration: 1000, composite: 'add' }); In the example above, the scale animation would not yet have been reduced to a single interpolated value, so the DCHECK for is_single_ would fail. This CL fixes the logic to perform an interpolation in that case. Bug: 979952 Change-Id: I36a3221c55aa3d98281a21a4ac93d95d61c5a1ff Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1750200 Reviewed-by: Kevin Ellis <kevers@chromium.org> Commit-Queue: Stephen McGruer <smcgruer@chromium.org> Cr-Commit-Position: refs/heads/master@{#686789}
web-platform-tests · Aug 14, 2019 · eba08b2 · eba08b2
1 parent a06709f
commit eba08b2
Showing 1 changed file with 38 additions and 0 deletions.
diff --git a/css/css-transforms/animation/composited-transform.html b/css/css-transforms/animation/composited-transform.html
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+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Composition of transform animations</title>
+<link rel="help" href="https://drafts.csswg.org/css-transforms-2/#combining-transform-lists">
+<meta name="assert" content="transform animations should composite correctly">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<div id="target"><div>
+
+<script>
+test(() => {
+  var anim1 = target.animate(
+      { transform: [ 'translateX(0)', 'translateX(100px)' ]},
+      1000
+  );
+  var anim2 = target.animate(
+      { transform: [ 'translateY(0)', 'translateY(100px)' ]},
+      {duration: 1000, composite: 'add'}
+  );
+
+  anim1.pause();
+  anim2.pause();
+
+  anim1.currentTime = 200;
+  anim2.currentTime = 800;
+
+  // The computation here should be:
+  //   underlying_value = 'translateX(0)' --> 'translateX(100px)' @ 0.2
+  //                    = 'translateX(20px)'
+  //   final_value = 0.2 * ('translateX(20px) translateY(0)') +
+  //                 0.8 * ('translateX(20px) translateY(100px)')
+  //               = 'translateX(20px) translateY(80px)'
+  //               = 'matrix(1, 0, 0, 1, 20, 80)'
+  assert_equals(getComputedStyle(target).transform, 'matrix(1, 0, 0, 1, 20, 80)')
+}, 'An additive transform animation on-top of a replace transform animation ' +
+    'should composite correctly');
+</script>