Implement difference clip rects with window rectangles

include/gpu/GrClip.h

Index: include/gpu/GrClip.h
diff --git a/include/gpu/GrClip.h b/include/gpu/GrClip.h
index a6a0a665bdca0174f5937bca753eb662a9a7ee34..26a88b3b7e403eaa6c18bda55f7b15d55556ab63 100644
--- a/include/gpu/GrClip.h
+++ b/include/gpu/GrClip.h
@@ -10,6 +10,7 @@
 
 #include "GrFragmentProcessor.h"
 #include "GrTypesPriv.h"
+#include "GrWindowRectangles.h"
 
 class GrDrawContext;
 
@@ -25,6 +26,7 @@ public:
     }
 
     const GrScissorState& scissorState() const { return fScissorState; }
+    const GrWindowRectangles& windows() const { return fWindows; }
     GrFragmentProcessor* clipCoverageFragmentProcessor() const { return fClipCoverageFP.get(); }
     bool hasStencilClip() const { return fHasStencilClip; }
 
@@ -35,6 +37,14 @@ public:
         return fScissorState.intersect(irect) && fClippedDrawBounds.intersect(SkRect::Make(irect));
     }
 
+    /**
+     * Adds an exclusive window rectangle to the clip. It is not currently supported to switch the
+     * windows to inclusive mode.
+     */
+    void addWindowRectangle(const SkIRect& window, const GrCaps& caps) {
+        fWindows.addWindow(window, caps);
+    }
+
     void addCoverageFP(sk_sp<GrFragmentProcessor> fp) {
         SkASSERT(!fClipCoverageFP);
         fClipCoverageFP = fp;
@@ -53,6 +63,7 @@ public:
 
 private:
     GrScissorState             fScissorState;
+    GrWindowRectangles         fWindows;
     sk_sp<GrFragmentProcessor> fClipCoverageFP;
     bool                       fHasStencilClip;
     SkRect                     fClippedDrawBounds;