Make skpaint->grpaint flow work for composing draws

src/gpu/SkGrPriv.h

 /*
  * 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 SkGrPriv_DEFINED
 #define SkGrPriv_DEFINED
 
 #include "GrTypes.h"
-#include "SkPoint.h"
+#include "SkImageInfo.h"
+#include "SkXfermode.h"
 
 class GrCaps;
+class GrContext;
+class GrFragmentProcessor;
+class GrPaint;
 class GrUniqueKey;
+class SkPaint;
+class SkMatrix;
+struct SkIRect;
 
 /**
  *  Our key includes the offset, width, and height so that bitmaps created by extractSubset()
  *  are unique.
  *
  *  The imageID is in the shared namespace (see SkNextID::ImageID()
  *      - SkBitmap/SkPixelRef
  *      - SkImage
  *      - SkImageGenerator
  *
  *  Note: width/height must fit in 16bits for this impl.
  */
 void GrMakeKeyFromImageID(GrUniqueKey* key, uint32_t imageID, const SkIRect& imageBounds,
                           const GrCaps&, SkImageUsageType);
 
+/** Converts an SkPaint to a GrPaint for a given GrContext. The matrix is required in order
+    to convert the SkShader (if any) on the SkPaint. */
+bool SkPaintToGrPaint(GrContext*,
+                      const SkPaint& skPaint,
+                      const SkMatrix& viewM,
+                      GrPaint* grPaint);
+
+/** Ignores the SkShader (if any) on skPaint. */
+bool SkPaintToGrPaintNoShader(GrContext* context,
+                              const SkPaint& skPaint,
+                              GrPaint* grPaint);
+
+/** Replaces the SkShader (if any) on skPaint with the passed in GrFragmentProcessor. The processor
+    should expect an unpremul input color and produce a premultiplied output color. */
+bool SkPaintToGrPaintReplaceShader(GrContext*,
+                                   const SkPaint& skPaint,
+                                   const GrFragmentProcessor* shaderFP,
+                                   GrPaint* grPaint);
+
+/** Blends the SkPaint's shader (or color if no shader) with the color which specified via a
+    GrBatch's GrPrimitiveProcesssor. Currently there is a bool param to indicate whether the
+    primitive color is the dst or src color to the blend in order to work around differences between
+    drawVertices and drawAtlas.
+ */
+bool SkPaintToGrPaintWithXfermode(GrContext* context,
+                                  const SkPaint& skPaint,
+                                  const SkMatrix& viewM,
+                                  SkXfermode::Mode primColorMode,
+                                  bool primitiveIsSrc,
+                                  GrPaint* grPaint);
+
 #endif