extend SkShader to report a luminance-color to be used for gamma correction

src/core/SkShader.cpp

 /*
  * 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.
  */
 
 #include "SkBitmapProcShader.h"
 #include "SkEmptyShader.h"
 #include "SkReadBuffer.h"
@@ skipping 61 matching lines @@
     total.setConcat(*rec.fMatrix, fLocalMatrix);
 
     const SkMatrix* m = &total;
     if (rec.fLocalMatrix) {
         total.setConcat(*m, *rec.fLocalMatrix);
         m = &total;
     }
     return m->invert(totalInverse);
 }
 
+bool SkShader::asLuminanceColor(SkColor* colorPtr) const {
+    SkColor storage;
+    if (NULL == colorPtr) {
+        colorPtr = &storage;
+    }
+    if (this->onAsLuminanceColor(colorPtr)) {
+        *colorPtr = SkColorSetA(*colorPtr, 0xFF);   // we only return opaque
+        return true;
+    }
+    return false;
+}
+
 SkShader::Context* SkShader::createContext(const ContextRec& rec, void* storage) const {
     if (!this->computeTotalInverse(rec, NULL)) {
         return NULL;
     }
     return this->onCreateContext(rec, storage);
 }
 
 SkShader::Context* SkShader::onCreateContext(const ContextRec& rec, void*) const {
     return NULL;
 }
@@ skipping 295 matching lines @@
 #include "SkEmptyShader.h"
 
 void SkEmptyShader::toString(SkString* str) const {
     str->append("SkEmptyShader: (");
 
     this->INHERITED::toString(str);
 
     str->append(")");
 }
 #endif