Fix drawVertices when there is a paint alpha

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
 
@@ skipping 36 matching lines @@
  */
 void GrMakeKeyFromImageID(GrUniqueKey* key, uint32_t imageID, const SkIRect& imageBounds,
                           const GrCaps&, SkImageUsageType);
 
 /**
  *  Given an "unstretched" key, and a stretch rec, produce a stretched key.
  */
 bool GrMakeStretchedKey(const GrUniqueKey& origKey, const SkGrStretch&, GrUniqueKey* stretchedKey);
 
 /** 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. */
+    to convert the SkShader (if any) on the SkPaint. The primitive itself has no color. */
 bool SkPaintToGrPaint(GrContext*,
                       const SkPaint& skPaint,
                       const SkMatrix& viewM,
                       GrPaint* grPaint);
 
-/** Ignores the SkShader (if any) on skPaint. */
+/** Same as above but 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. */
+    should expect an unpremul input color and produce a premultiplied output color. There is
+    no primitive 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.
- */
+    drawVertices and drawAtlas. */
 bool SkPaintToGrPaintWithXfermode(GrContext* context,
                                   const SkPaint& skPaint,
                                   const SkMatrix& viewM,
                                   SkXfermode::Mode primColorMode,
                                   bool primitiveIsSrc,
                                   GrPaint* grPaint);
 
+/** This is used when there is a primitive color, but the shader should be ignored. Currently,
+    the expectation is that the primitive color will be premultiplied, though it really should be
+    unpremultiplied so that interpolation is done in unpremul space. The paint's alpha will be
+    applied to the primitive color after interpolation. */
+inline bool SkPaintToGrPaintWithPrimitiveColor(GrContext* context, const SkPaint& skPaint,
+                                               GrPaint* grPaint) {
+    return SkPaintToGrPaintWithXfermode(context, skPaint, SkMatrix::I(), SkXfermode::kDst_Mode,
+                                        false, grPaint);
+}
+
 bool GrTextureUsageSupported(const GrCaps&, int width, int height, SkImageUsageType);
 
 #endif