Add flag to gradients to interpolate colors in premul space. Experimental API to encapsulate the sh…

include/effects/SkGradientShader.h

Index: include/effects/SkGradientShader.h
diff --git a/include/effects/SkGradientShader.h b/include/effects/SkGradientShader.h
index dbeb2fb069818b4e9dab862bd66cb2aecb3a6f51..ed0f1bf75b5454e5809fbfb1f09449d881b71110 100644
--- a/include/effects/SkGradientShader.h
+++ b/include/effects/SkGradientShader.h
@@ -1,4 +1,3 @@
-
 /*
  * Copyright 2006 The Android Open Source Project
  *
@@ -6,7 +5,6 @@
  * found in the LICENSE file.
  */
 
-
 #ifndef SkGradientShader_DEFINED
 #define SkGradientShader_DEFINED
 
@@ -21,6 +19,15 @@ class SkUnitMapper;
 */
 class SK_API SkGradientShader {
 public:
+    enum Flags {
+        /** By default gradients will interpolate their colors in unpremul space
+         *  and then premultiply each of the results. By setting this flag, the
+         *  gradients will premultiply their colors first, and then interpolate
+         *  between them.
+         */
+        kInterpolateColorsInPremul_Flag = 1 << 0,
+    };
+
     /** Returns a shader that generates a linear gradient between the two
         specified points.
         <p />
@@ -38,10 +45,11 @@ public:
         @param  mode    The tiling mode
         @param  mapper  May be NULL. Callback to modify the spread of the colors.
     */
-    static SkShader* CreateLinear(  const SkPoint pts[2],
-                                    const SkColor colors[], const SkScalar pos[], int count,
-                                    SkShader::TileMode mode,
-                                    SkUnitMapper* mapper = NULL);
+    static SkShader* CreateLinear(const SkPoint pts[2],
+                                  const SkColor colors[], const SkScalar pos[], int count,
+                                  SkShader::TileMode mode,
+                                  SkUnitMapper* mapper = NULL,
+                                  uint32_t flags = 0);
 
     /** Returns a shader that generates a radial gradient given the center and radius.
         <p />
@@ -60,10 +68,11 @@ public:
         @param  mode    The tiling mode
         @param  mapper  May be NULL. Callback to modify the spread of the colors.
     */
-    static SkShader* CreateRadial(  const SkPoint& center, SkScalar radius,
-                                    const SkColor colors[], const SkScalar pos[], int count,
-                                    SkShader::TileMode mode,
-                                    SkUnitMapper* mapper = NULL);
+    static SkShader* CreateRadial(const SkPoint& center, SkScalar radius,
+                                  const SkColor colors[], const SkScalar pos[], int count,
+                                  SkShader::TileMode mode,
+                                  SkUnitMapper* mapper = NULL,
+                                  uint32_t flags = 0);
 
     /** Returns a shader that generates a radial gradient given the start position, start radius, end position and end radius.
         <p />
@@ -92,7 +101,8 @@ public:
                                           const SkColor colors[],
                                           const SkScalar pos[], int count,
                                           SkShader::TileMode mode,
-                                          SkUnitMapper* mapper = NULL);
+                                          SkUnitMapper* mapper = NULL,
+                                          uint32_t flags = 0);
 
     /**
      *  Returns a shader that generates a conical gradient given two circles, or
@@ -101,13 +111,14 @@ public:
      *  http://dev.w3.org/html5/2dcontext/#dom-context-2d-createradialgradient
      */
     static SkShader* CreateTwoPointConical(const SkPoint& start,
-                                          SkScalar startRadius,
-                                          const SkPoint& end,
-                                          SkScalar endRadius,
-                                          const SkColor colors[],
-                                          const SkScalar pos[], int count,
-                                          SkShader::TileMode mode,
-                                          SkUnitMapper* mapper = NULL);
+                                           SkScalar startRadius,
+                                           const SkPoint& end,
+                                           SkScalar endRadius,
+                                           const SkColor colors[],
+                                           const SkScalar pos[], int count,
+                                           SkShader::TileMode mode,
+                                           SkUnitMapper* mapper = NULL,
+                                           uint32_t flags = 0);
 
     /** Returns a shader that generates a sweep gradient given a center.
         <p />
@@ -127,7 +138,8 @@ public:
     */
     static SkShader* CreateSweep(SkScalar cx, SkScalar cy,
                                  const SkColor colors[], const SkScalar pos[],
-                                 int count, SkUnitMapper* mapper = NULL);
+                                 int count, SkUnitMapper* mapper = NULL,
+                                 uint32_t flags = 0);
 
     SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
 };