Bug 1236750 - Add some specialized typedefs of Matrix4x4 to represent layer transform matrices. r=kats

Also add a related PixelCastJustification and a utility function.

gfx/layers/LayersTypes.h

@@ -13,6 +13,7 @@
 #include "mozilla/layers/GonkNativeHandle.h"
 #endif
 
+#include "Units.h"
 #include "mozilla/gfx/Point.h"          // for IntPoint
 #include "mozilla/TypedEnumBits.h"
 #include "nsRegion.h"
@@ -284,6 +285,22 @@ enum TextureDumpMode {
   DoNotCompress  // dump texture uncompressed
 };
 
+// Some specialized typedefs of Matrix4x4Typed.
+typedef gfx::Matrix4x4Typed<LayerPixel, CSSTransformedLayerPixel> CSSTransformMatrix;
+// Several different async transforms can contribute to a layer's transform
+// (specifically, an async animation can contribute a transform, and each APZC
+// that scrolls a layer can contribute async scroll/zoom and overscroll
+// transforms).
+// To try to model this with typed units, we represent individual async
+// transforms as ParentLayer -> ParentLayer transforms (aliased as
+// AsyncTransformComponentMatrix), and we represent the product of all of them
+// as a CSSTransformLayer -> ParentLayer transform (aliased as
+// AsyncTransformMatrix). To create an AsyncTransformMatrix from component
+// matrices, a ViewAs operation is needed. A MultipleAsyncTransforms
+// PixelCastJustification is provided for this purpose.
+typedef gfx::Matrix4x4Typed<ParentLayerPixel, ParentLayerPixel> AsyncTransformComponentMatrix;
+typedef gfx::Matrix4x4Typed<CSSTransformedLayerPixel, ParentLayerPixel> AsyncTransformMatrix;
+
 } // namespace layers
 } // namespace mozilla
 

gfx/layers/apz/src/APZUtils.h

@@ -8,6 +8,8 @@
 #define mozilla_layers_APZUtils_h
 
 #include <stdint.h>                     // for uint32_t
+#include "LayersTypes.h"
+#include "UnitTransforms.h"
 #include "mozilla/gfx/Point.h"
 #include "mozilla/FloatingPoint.h"
 
@@ -61,6 +63,16 @@ static bool IsZero(const gfx::PointTyped<Units>& aPoint)
       && FuzzyEqualsAdditive(aPoint.y, 0.0f, COORDINATE_EPSILON);
 }
 
+// Deem an AsyncTransformComponentMatrix (obtained by multiplying together
+// one or more AsyncTransformComponentMatrix objects) as constituting a
+// complete async transform.
+inline AsyncTransformMatrix
+CompleteAsyncTransform(const AsyncTransformComponentMatrix& aMatrix)
+{
+  return ViewAs<AsyncTransformMatrix>(aMatrix,
+      PixelCastJustification::MultipleAsyncTransforms);
+}
+
 } // namespace layers
 } // namespace mozilla
 

layout/base/UnitTransforms.h

@@ -47,7 +47,11 @@ enum class PixelCastJustification : uint8_t {
   LayoutDeviceIsScreenForTabDims,
   // A combination of LayoutDeviceIsScreenForBounds and
   // ScreenIsParentLayerForRoot, which is how we're using it.
-  LayoutDeviceIsParentLayerForRCDRSF
+  LayoutDeviceIsParentLayerForRCDRSF,
+  // Used to treat the product of AsyncTransformComponentMatrix objects
+  // as an AsyncTransformMatrix. See the definitions of these matrices in
+  // LayersTypes.h for details.
+  MultipleAsyncTransforms
 };
 
 template <class TargetUnits, class SourceUnits>