extend compose-colorfilter to 4f

include/core/SkColor.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkColor_DEFINED
 #define SkColor_DEFINED
 
@@ skipping 142 matching lines @@
     dependent order, to match the format of kARGB32 bitmaps.
 */
 SK_API SkPMColor SkPreMultiplyColor(SkColor c);
 
 /** Define a function pointer type for combining two premultiplied colors
 */
 typedef SkPMColor (*SkXfermodeProc)(SkPMColor src, SkPMColor dst);
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
+struct SkColor4f;
+
 /*
  *  The float values are 0...1 premultiplied
  */
 struct SkPM4f {
     enum {
         A = SK_A32_SHIFT/8,
         R = SK_R32_SHIFT/8,
         G = SK_G32_SHIFT/8,
         B = SK_B32_SHIFT/8,
     };
     float fVec[4];
 
     float a() const { return fVec[A]; }
 
+    SkColor4f unpremul() const;
+
     static SkPM4f FromPMColor(SkPMColor);
 
 #ifdef SK_DEBUG
     void assertIsUnit() const;
 #else
     void assertIsUnit() const {}
 #endif
 };
 
 /*
@@ skipping 19 matching lines @@
     static SkColor4f FromColor(SkColor);
 
     SkColor4f pin() const {
         return Pin(fA, fR, fG, fB);
     }
 
     SkPM4f premul() const;
 };
 
 #endif