Implement difference clip rects with window rectangles

src/gpu/GrAppliedClip.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrAppliedClip_DEFINED
+#define GrAppliedClip_DEFINED
+
+#include "GrWindowRectangles.h"
+
+/**
+ * Produced by GrClip. It provides a set of modifications to the drawing state that are used to
+ * create the final GrPipeline for a GrBatch.
+ */
+class GrAppliedClip : public SkNoncopyable {
+public:
+    GrAppliedClip(const SkRect& drawBounds)
+        : fHasStencilClip(false)
+        , fClippedDrawBounds(drawBounds) {
+    }
+
+    const GrScissorState& scissorState() const { return fScissorState; }
+    const GrWindowRectangles& windowRects() const { return fWindowRects; }
+    GrFragmentProcessor* clipCoverageFragmentProcessor() const { return fClipCoverageFP.get(); }
+    bool hasStencilClip() const { return fHasStencilClip; }
+
+    /**
+     * Intersects the applied clip with the provided rect. Returns false if the draw became empty.
+     */
+    bool addScissor(const SkIRect& irect) {
+        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) {
+        fWindowRects.addWindow(window);
+    }
+
+    void addCoverageFP(sk_sp<GrFragmentProcessor> fp) {
+        SkASSERT(!fClipCoverageFP);
+        fClipCoverageFP = fp;
+    }
+
+    void addStencilClip() {
+        SkASSERT(!fHasStencilClip);
+        fHasStencilClip = true;
+    }
+
+    /**
+     * Returns the device bounds of the draw after clip has been applied. TODO: Ideally this would
+     * consider the combined effect of all clipping techniques in play (scissor, stencil, fp, etc.).
+     */
+    const SkRect& clippedDrawBounds() const { return fClippedDrawBounds; }
+
+private:
+    GrScissorState             fScissorState;
+    GrWindowRectangles         fWindowRects;
+    sk_sp<GrFragmentProcessor> fClipCoverageFP;
+    bool                       fHasStencilClip;
+    SkRect                     fClippedDrawBounds;
+    typedef SkNoncopyable INHERITED;
+};
+
+#endif