add peekPixels to canvas

include/core/SkCanvas.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 SkCanvas_DEFINED
 #define SkCanvas_DEFINED
 
@@ skipping 108 matching lines @@
 
     /**
      * Return the GPU context of the device that is associated with the canvas.
      * For a canvas with non-GPU device, NULL is returned.
      */
     GrContext* getGrContext();
 
     ///////////////////////////////////////////////////////////////////////////
 
     /**
+     *  If the canvas has direct access to its pixels (i.e. they are in local
+     *  RAM) return the const-address of those pixels, and if not null, return

[hal.canary, 2014/02/12 15:11:02]

And if the canvas has a concept of "pixels" at all.

[reed1, 2014/02/12 17:24:10]

Done.

+     *  the ImageInfo and rowBytes. The returned address is only valid while
+     *  the canvas object is in scope and unchanged. Any API calls made on the
+     *  canvas can invalidate this address.
+     *
+     *  On failure, returns NULL and the info and rowBytes parameters are
+     *  ignored.
+     */
+    const void* peekPixels(SkImageInfo* info, size_t* rowBytes);
+
+    /**
      * This enum can be used with read/writePixels to perform a pixel ops to or
      * from an 8888 config other than Skia's native config (SkPMColor). There
      * are three byte orders supported: native, BGRA, and RGBA. Each has a
      * premultiplied and unpremultiplied variant.
      *
      * Components of a 8888 pixel can be packed/unpacked from a 32bit word using
      * either byte offsets or shift values. Byte offsets are endian-invariant
      * while shifts are not. BGRA and RGBA configs are defined by byte
      * orderings. The native config is defined by shift values (SK_A32_SHIFT,
      * ..., SK_B32_SHIFT).
@@ skipping 873 matching lines @@
         intptr_t          fStorage[32];
         class SkDrawIter* fImpl;    // this points at fStorage
         SkPaint           fDefaultPaint;
         bool              fDone;
     };
 
 protected:
     // default impl defers to getDevice()->newSurface(info)
     virtual SkSurface* onNewSurface(const SkImageInfo&);
 
+    // default impl defers to its device
+    virtual const void* onPeekPixels(SkImageInfo*, size_t* rowBytes);
+
     // Returns the canvas to be used by DrawIter. Default implementation
     // returns this. Subclasses that encapsulate an indirect canvas may
     // need to overload this method. The impl must keep track of this, as it
     // is not released or deleted by the caller.
     virtual SkCanvas* canvasForDrawIter();
 
     // Clip rectangle bounds. Called internally by saveLayer.
     // returns false if the entire rectangle is entirely clipped out
     // If non-NULL, The imageFilter parameter will be used to expand the clip
     // and offscreen bounds for any margin required by the filter DAG.
@@ skipping 168 matching lines @@
             fCanvas->endCommentGroup();
         }
     }
 
 private:
     SkCanvas* fCanvas;
 };
 #define SkAutoCommentBlock(...) SK_REQUIRE_LOCAL_VAR(SkAutoCommentBlock)
 
 #endif