alpha threshold bitmap shader

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
@@ skipping 300 matching lines @@
         SkScalar*   fColorOffsets;  //!< The unit offset for color transitions.
         SkPoint     fPoint[2];      //!< Type specific, see above.
         SkScalar    fRadius[2];     //!< Type specific, see above.
         TileMode    fTileMode;      //!< The tile mode used.
         uint32_t    fGradientFlags; //!< see SkGradientShader::Flags
     };
 
     virtual GradientType asAGradient(GradientInfo* info) const;
 
     /**
-     *  If the shader subclass has a GrEffect implementation, this installs an effect on the stage.
-     *  The GrContext may be used by the effect to create textures. The GPU device does not call
-     *  setContext. Instead we pass the paint here in case the shader needs paint info.
+     *  If the shader subclass has a GrEffect implementation, this resturns the effect to install.
+     *  The incoming color to the effect has r=g=b=a all extracted from the SkPaint's alpha.
+     *  The output color should be the computed SkShader premul color modulated by the incoming
+     *  color. The GrContext may be used by the effect to create textures. The GPU device does not
+     *  call setContext. Instead we pass the SkPaint here in case the shader needs paint info.
      */
     virtual GrEffectRef* asNewEffect(GrContext* context, const SkPaint& paint) const;
 
     //////////////////////////////////////////////////////////////////////////
     //  Factory methods for stock shaders
 
     /** Call this to create a new shader that will draw with the specified bitmap.
      *
      *  If the bitmap cannot be used (e.g. has no pixels, or its dimensions
      *  exceed implementation limits (currently at 64K - 1)) then SkEmptyShader
@@ skipping 34 matching lines @@
     SkDEBUGCODE(SkBool8 fInSetContext;)
 
     static SkShader* CreateBitmapShader(const SkBitmap& src,
                                         TileMode, TileMode,
                                         void* storage, size_t storageSize);
     friend class SkAutoBitmapShaderInstall;
     typedef SkFlattenable INHERITED;
 };
 
 #endif