Bug 1430884 - Throttle transform animations without %0 or 100% keyframe. r=birtles

MozReview-Commit-ID: 3vLAlSkLz97

--HG--
extra : rebase_source : 424a94ace113c3383fd91300802973ba60da5f7d

dom/animation/KeyframeEffect.cpp

@@ -1617,9 +1617,25 @@ KeyframeEffect::CalculateCumulativeChangeHint(const ComputedStyle* aComputedStyl
       // on invisible elements because we can't calculate the change hint for
       // such properties until we compose it.
       if (!segment.HasReplaceableValues()) {
-        mCumulativeChangeHint = ~nsChangeHint_Hints_CanIgnoreIfNotVisible;
-        return;
+        if (property.mProperty != eCSSProperty_transform) {
+          mCumulativeChangeHint = ~nsChangeHint_Hints_CanIgnoreIfNotVisible;
+          return;
+        }
+        // We try a little harder to optimize transform animations simply
+        // because they are so common (the second-most commonly animated
+        // property at the time of writing).  So if we encounter a transform
+        // segment that needs composing with the underlying value, we just add
+        // all the change hints a transform animation is known to be able to
+        // generate.
+        mCumulativeChangeHint |= nsChangeHint_AddOrRemoveTransform |
+                                 nsChangeHint_RepaintFrame |
+                                 nsChangeHint_UpdateContainingBlock |
+                                 nsChangeHint_UpdateOverflow |
+                                 nsChangeHint_UpdatePostTransformOverflow |
+                                 nsChangeHint_UpdateTransformLayer;
+        continue;
       }
+
       RefPtr<ComputedStyle> fromContext =
         CreateComputedStyleForAnimationValue(property.mProperty,
                                              segment.mFromValue,

dom/animation/test/mozilla/file_restyles.html

@@ -1774,6 +1774,25 @@ waitForAllPaints(() => {
     await ensureElementRemoval(div);
   });
 
+  add_task(async function restyling_transform_aimations_on_invisible_element() {
+    // 'opacity: 0' prevents transform animations to be sent to the compositor.
+    const div = addDiv(null, { style: 'visibility: hidden; opacity: 0' });
+
+    const animation =
+      div.animate([ { transform: 'rotate(360deg)' } ],
+                  { duration: 100 * MS_PER_SEC,
+                    iterations: Infinity });
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Transform animations without 100% keyframe on visibility hidden ' +
+       'element should be throttled');
+    await ensureElementRemoval(div);
+  });
+
 });
 
 </script>

layout/style/nsStyleStruct.cpp

@@ -3694,6 +3694,9 @@ CompareTransformValues(const RefPtr<nsCSSValueSharedList>& aList,
                        const RefPtr<nsCSSValueSharedList>& aNewList)
 {
   nsChangeHint result = nsChangeHint(0);
+
+  // Note: If we add a new change hint for transform changes here, we have to
+  // modify KeyframeEffect::CalculateCumulativeChangeHint too!
   if (!aList != !aNewList || (aList && *aList != *aNewList)) {
     result |= nsChangeHint_UpdateTransformLayer;
     if (aList && aNewList) {
@@ -3818,6 +3821,10 @@ nsStyleDisplay::CalcDifference(const nsStyleDisplay& aNewData) const
     // We do not need to apply nsChangeHint_UpdateTransformLayer since
     // nsChangeHint_RepaintFrame will forcibly invalidate the frame area and
     // ensure layers are rebuilt (or removed).
+    //
+    // Note: If we add a new change hint for transform changes here or in
+    // CompareTransformValues(), we have to modify
+    // KeyframeEffect::CalculateCumulativeChangeHint too!
     hint |= nsChangeHint_UpdateContainingBlock |
             nsChangeHint_AddOrRemoveTransform |
             nsChangeHint_UpdateOverflow |