add ways to peer into an image to get its pixels

include/core/SkImage.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImage_DEFINED
 #define SkImage_DEFINED
 
@@ skipping 58 matching lines @@
     /**
      *  Draw the image, cropped to the src rect, to the dst rect of a canvas.
      *  If src is larger than the bounds of the image, the rest of the image is
      *  filled with transparent black pixels.
      *
      *  See SkCanvas::drawBitmapRectToRect for similar behavior.
      */
     void draw(SkCanvas*, const SkRect* src, const SkRect& dst, const SkPaint*);
 
     /**
+     *  If the image 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
+     *  the ImageInfo and rowBytes. The returned address is only valid while
+     *  the image object is in scope.
+     *
+     *  On failure, returns NULL and the info and rowBytes parameters are
+     *  ignored.
+     */
+    const void* peekPixels(SkImageInfo* info, size_t* rowBytes) const;
+    
+    /**
      *  Encode the image's pixels and return the result as a new SkData, which
      *  the caller must manage (i.e. call unref() when they are done).
      *
      *  If the image type cannot be encoded, or the requested encoder type is
      *  not supported, this will return NULL.
      */
     SkData* encode(SkImageEncoder::Type t = SkImageEncoder::kPNG_Type,
                    int quality = 80) const;
 
 protected:
     SkImage(int width, int height) :
         fWidth(width),
         fHeight(height),
         fUniqueID(NextUniqueID()) {
 
         SkASSERT(width >= 0);
         SkASSERT(height >= 0);
     }
 
 private:
     const int       fWidth;
     const int       fHeight;
     const uint32_t  fUniqueID;
 
     static uint32_t NextUniqueID();
 
     typedef SkRefCnt INHERITED;
+
+    /**
+     *  Return a copy of the image's pixels, limiting them to the subset
+     *  rectangle's intersection wit the image bounds. If subset is NULL, then
+     *  the entire image will be considered.
+     *
+     *  If the bitmap's pixels have already been allocated, then readPixels()
+     *  will succeed only if it can support converting the image's pixels into
+     *  the bitmap's ColorType/AlphaType. Any pixels in the bitmap that do not
+     *  intersect with the image's bounds and the subset (if not null) will be
+     *  left untouched.
+     *
+     *  If the bitmap is initially empty/unallocated, then it will be allocated
+     *  using the default allocator, and the ColorType/AlphaType will be chosen
+     *  to most closely fit the image's configuration.
+     *
+     *  On failure, false will be returned, and bitmap will unmodified.
+     */
+    // On ice for now:
+    // - should it respect the particular colortype/alphatype of the src
+    // - should it have separate entrypoints for preallocated and not bitmaps?
+    // - isn't it enough to allow the caller to draw() the image into a canvas?
+    bool readPixels(SkBitmap* bitmap, const SkIRect* subset = NULL) const;
 };
 
 #endif