Bug 1394308 - Apply inherited scale for OMTA to support layers-free, r=kats

Expose the API to get/set inherited scale from stacking context and we can
use these APIs to calculate correct scale for OMTA

MozReview-Commit-ID: DZEkodHTy8v

--HG--
extra : rebase_source : be3c978c8f48c9b1bfcd01cff6bb8200092b5e60

gfx/layers/wr/StackingContextHelper.cpp

@@ -102,6 +102,7 @@ StackingContextHelper::StackingContextHelper(const StackingContextHelper& aParen
     mTransform.PostScale(aParentSC.mXScale, aParentSC.mYScale, 1.0);
     mTransform.NudgeToIntegersFixedEpsilon();
 
+    // Calculate the correct scale for current stacking context
     gfx::Size scale = mTransform.As2D().ScaleFactors(true);
 
     // Restore the scale to default if the scale is too small
@@ -112,7 +113,7 @@ StackingContextHelper::StackingContextHelper(const StackingContextHelper& aParen
 
     mTransform.PreScale(1.0f/scale.width, 1.0f/scale.height, 1.0);
 
-    // Store the inherited scale if has
+    // Store the inherited scale for child
     this->mXScale = scale.width;
     this->mYScale = scale.height;
   } else {

gfx/layers/wr/StackingContextHelper.h

@@ -83,6 +83,18 @@ public:
   // Same but rounds the rectangle to ints after transforming.
   wr::LayoutRect ToRelativeLayoutRectRounded(const LayoutDeviceRect& aRect) const;
 
+  // Export the inherited scale
+  gfx::Size GetInheritedScale() const {
+    return gfx::Size(mXScale, mYScale);
+  }
+
+  // Provide interface to setup the inherited scale to support
+  // special cases, like OMTA
+  void SetInheritedScale(const gfx::Size& aScale) {
+    mXScale = aScale.width;
+    mYScale = aScale.height;
+  }
+
   bool IsBackfaceVisible() const { return mTransform.IsBackfaceVisible(); }
 
 private:

layout/painting/nsDisplayList.cpp

@@ -7812,15 +7812,6 @@ nsDisplayTransform::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBu
     // transform animation, the transform value will be resolved
     // after animation sampling on the compositor
     transformForSC = nullptr;
-
-    // Pass default transform to compositor in case gecko fails to
-    // get animated value after animation sampling.
-    OptionalTransform transformForCompositor = newTransformMatrix;
-
-    OpAddCompositorAnimations
-      anim(CompositorAnimations(animationInfo.GetAnimations(), animationsId),
-           transformForCompositor, void_t());
-    aManager->WrBridge()->AddWebRenderParentCommand(anim);
   }
 
   gfx::Matrix4x4Typed<LayerPixel, LayerPixel> boundTransform = ViewAs< gfx::Matrix4x4Typed<LayerPixel, LayerPixel> >(newTransformMatrix);
@@ -7841,6 +7832,32 @@ nsDisplayTransform::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBu
                            nullptr,
                            filters);
 
+  if (animationsId) {
+    // Get the inheritedScale from parent and pass the scale to compositor
+    // to get correct sampling result
+    gfx::Size scale = aSc.GetInheritedScale();
+    for (layers::Animation& animation : animationInfo.GetAnimations()) {
+      if (animation.property() == eCSSProperty_transform) {
+        TransformData& transformData = animation.data().get_TransformData();
+        transformData.inheritedXScale() = scale.width;
+        transformData.inheritedYScale() = scale.height;
+      }
+    }
+
+    // Pass default transform to compositor in case gecko fails to
+    // get animated value after animation sampling.
+    OptionalTransform transformForCompositor = newTransformMatrix;
+    OpAddCompositorAnimations
+      anim(CompositorAnimations(animationInfo.GetAnimations(), animationsId),
+           transformForCompositor, void_t());
+    aManager->WrBridge()->AddWebRenderParentCommand(anim);
+
+    // Since we passed a nullptr transformForSC to the StackingContextHelper,
+    // we now set up the correct inherited scale for the stacking context.
+    newTransformMatrix.PostScale(scale.width, scale.height, 1.0f);
+    sc.SetInheritedScale(newTransformMatrix.As2D().ScaleFactors(true));
+
+  }
   return mStoredList.CreateWebRenderCommands(aBuilder, sc, aParentCommands,
                                              aManager, aDisplayListBuilder);
 }