add ImageShader, sharing code with its Bitmap cousin

include/core/SkShader.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 SkShader_DEFINED
 #define SkShader_DEFINED
 
@@ skipping 395 matching lines @@
      *  and, if not NULL, the localMatrix. If not, return NULL and ignore the localMatrix parameter.
      *
      *  Note: the returned shader (if not NULL) will have been ref'd, and it is the responsibility
      *  of the caller to balance that with unref() when they are done.
      */
     virtual SkShader* refAsALocalMatrixShader(SkMatrix* localMatrix) const;
 
     SK_TO_STRING_VIRT()
     SK_DEFINE_FLATTENABLE_TYPE(SkShader)
 
+    // Should be protected, but sometimes a subclass needs to call it on another shader
+    bool computeTotalInverse(const ContextRec&, SkMatrix* totalInverse) const;

[f(malita), 2015/09/15 15:01:41]

Befriend SkBitmapProcShader instead?

+
 protected:
     void flatten(SkWriteBuffer&) const override;
 
-    bool computeTotalInverse(const ContextRec&, SkMatrix* totalInverse) const;
-
     /**
      *  Your subclass must also override contextSize() if it overrides onCreateContext().
      *  Base class impl returns NULL.
      */
     virtual Context* onCreateContext(const ContextRec&, void* storage) const;
 
     virtual bool onAsLuminanceColor(SkColor*) const {
         return false;
     }
 
     virtual bool onIsABitmap(SkBitmap*, SkMatrix*, TileMode[2]) const {
         return false;
     }
 
 private:
     // This is essentially const, but not officially so it can be modified in
     // constructors.
     SkMatrix fLocalMatrix;
 
     // So the SkLocalMatrixShader can whack fLocalMatrix in its SkReadBuffer constructor.
     friend class SkLocalMatrixShader;
 
     typedef SkFlattenable INHERITED;
 };
 
 #endif