Add a paint filter utility canvas (SkPaintFilterCanvas)

include/utils/SkPaintFilterCanvas.h

Index: include/utils/SkPaintFilterCanvas.h
diff --git a/include/utils/SkPaintFilterCanvas.h b/include/utils/SkPaintFilterCanvas.h
new file mode 100644
index 0000000000000000000000000000000000000000..942fbda8763d2cbaa7c623893748d1671aa91496
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+++ b/include/utils/SkPaintFilterCanvas.h
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+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkPaintFilterCanvas_DEFINED
+#define SkPaintFilterCanvas_DEFINED
+
+#include "SkNWayCanvas.h"
+
+/** \class SkPaintFilterCanvas
+
+    A utility proxy base class for implementing paint filters.
+*/
+class SK_API SkPaintFilterCanvas : public SkNWayCanvas {
+public:
+    SkPaintFilterCanvas(int width, int height);
+
+    enum Type {
+        kPaint_Type,
+        kPoint_Type,
+        kBitmap_Type,
+        kRect_Type,
+        kRRect_Type,
+        kDRRect_Type,
+        kOval_Type,
+        kPath_Type,
+        kPicture_Type,
+        kText_Type,
+        kTextBlob_Type,
+        kVertices_Type,
+        kPatch_Type,
+
+        kTypeCount
+    };
+
+protected:
+    /**
+     *  Called with the paint that will be used to draw the specified type.
+     *  The implementation may modify the paint as they wish.
+     *
+     *  Note: The base implementation calls onFilterPaint() for top-level/explicit paints only.
+     *        To also filter encapsulated paints (e.g. SkPicture, SkTextBlob), clients may need to
+     *        override the relevant methods (i.e. drawPicture, drawTextBlob).
+     */
+    virtual void onFilterPaint(SkPaint* paint, Type type) const = 0;
+
+    void onDrawPaint(const SkPaint&) override;
+    void onDrawPoints(PointMode, size_t count, const SkPoint pts[], const SkPaint&) override;
+    void onDrawRect(const SkRect&, const SkPaint&) override;
+    void onDrawRRect(const SkRRect&, const SkPaint&) override;
+    void onDrawDRRect(const SkRRect&, const SkRRect&, const SkPaint&) override;
+    void onDrawOval(const SkRect&, const SkPaint&) override;
+    void onDrawPath(const SkPath&, const SkPaint&) override;
+    void onDrawBitmap(const SkBitmap&, SkScalar left, SkScalar top, const SkPaint*) override;
+    void onDrawBitmapRect(const SkBitmap&, const SkRect* src, const SkRect& dst, const SkPaint*,
+                          DrawBitmapRectFlags flags) override;
+    void onDrawImage(const SkImage*, SkScalar left, SkScalar top, const SkPaint*) override;
+    void onDrawImageRect(const SkImage*, const SkRect* src, const SkRect& dst,
+                         const SkPaint*) override;
+    void onDrawBitmapNine(const SkBitmap&, const SkIRect& center, const SkRect& dst,
+                          const SkPaint*) override;
+    void onDrawSprite(const SkBitmap&, int left, int top, const SkPaint*) override;
+    void onDrawVertices(VertexMode vmode, int vertexCount,
+                              const SkPoint vertices[], const SkPoint texs[],
+                              const SkColor colors[], SkXfermode* xmode,
+                              const uint16_t indices[], int indexCount,
+                              const SkPaint&) override;
+    void onDrawPatch(const SkPoint cubics[12], const SkColor colors[4],
+                             const SkPoint texCoords[4], SkXfermode* xmode,
+                             const SkPaint& paint) override;
+    void onDrawPicture(const SkPicture*, const SkMatrix*, const SkPaint*) override;
+
+    void onDrawText(const void* text, size_t byteLength, SkScalar x, SkScalar y,
+                    const SkPaint&) override;
+    void onDrawPosText(const void* text, size_t byteLength, const SkPoint pos[],
+                       const SkPaint&) override;
+    void onDrawPosTextH(const void* text, size_t byteLength, const SkScalar xpos[],
+                        SkScalar constY, const SkPaint&) override;
+    void onDrawTextOnPath(const void* text, size_t byteLength, const SkPath& path,
+                          const SkMatrix* matrix, const SkPaint&) override;
+    void onDrawTextBlob(const SkTextBlob* blob, SkScalar x, SkScalar y,
+                        const SkPaint& paint) override;
+
+private:
+    class AutoPaintFilter;
+
+    typedef SkNWayCanvas INHERITED;
+};
+
+#endif