Bug 1149923 - Let 2D mask effect can check whether to use IntermediateSurface or not in its own logic. r=roc

gfx/2d/Matrix.h

@@ -379,11 +379,18 @@ public:
   /**
    * Returns true if the matrix has any transform other
    * than a translation or scale; this is, if there is
-   * no rotation.
+   * rotation.
    */
   bool HasNonAxisAlignedTransform() const {
       return !FuzzyEqual(_21, 0.0) || !FuzzyEqual(_12, 0.0);
   }
+
+  /**
+   * Returns true if the matrix has negative scaling (i.e. flip).
+   */
+  bool HasNegativeScaling() const {
+      return (_11 < 0.0) || (_22 < 0.0);
+  }
 };
 
 class Matrix4x4

gfx/layers/Layers.cpp

@@ -1224,12 +1224,30 @@ ContainerLayer::DefaultComputeEffectiveTransforms(const Matrix4x4& aTransformToS
     } else {
       useIntermediateSurface = false;
       gfx::Matrix contTransform;
-      if (!mEffectiveTransform.Is2D(&contTransform) ||
+      bool checkClipRect = false;
+      bool checkMaskLayers = false;
+
+      if (!mEffectiveTransform.Is2D(&contTransform)) {
+        // In 3D case, always check if we should use IntermediateSurface.
+        checkClipRect = true;
+        checkMaskLayers = true;
+      } else {
 #ifdef MOZ_GFX_OPTIMIZE_MOBILE
-        !contTransform.PreservesAxisAlignedRectangles()) {
+        if (!contTransform.PreservesAxisAlignedRectangles()) {
 #else
-        gfx::ThebesMatrix(contTransform).HasNonIntegerTranslation()) {
+        if (gfx::ThebesMatrix(contTransform).HasNonIntegerTranslation()) {
 #endif
+          checkClipRect = true;
+        }
+        /* In 2D case, only translation and/or positive scaling can be done w/o using IntermediateSurface.
+         * Otherwise, when rotation or flip happen, we should check whether to use IntermediateSurface.
+         */
+        if (contTransform.HasNonAxisAlignedTransform() || contTransform.HasNegativeScaling()) {
+          checkMaskLayers = true;
+        }
+      }
+
+      if (checkClipRect || checkMaskLayers) {
         for (Layer* child = GetFirstChild(); child; child = child->GetNextSibling()) {
           const Maybe<ParentLayerIntRect>& clipRect = child->GetEffectiveClipRect();
           /* We can't (easily) forward our transform to children with a non-empty clip
@@ -1237,8 +1255,11 @@ ContainerLayer::DefaultComputeEffectiveTransforms(const Matrix4x4& aTransformToS
            * the calculations performed by CalculateScissorRect above.
            * Nor for a child with a mask layer.
            */
-          if ((clipRect && !clipRect->IsEmpty() && !child->GetVisibleRegion().IsEmpty()) ||
-              child->HasMaskLayers()) {
+          if (checkClipRect && (clipRect && !clipRect->IsEmpty() && !child->GetVisibleRegion().IsEmpty())) {
+            useIntermediateSurface = true;
+            break;
+          }
+          if (checkMaskLayers && child->HasMaskLayers()) {
             useIntermediateSurface = true;
             break;
           }