add NewRasterDirect for creating a canvas drawing to pre-allocated pixels

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 70 matching lines @@
      *  Note: it is valid to request a supported ImageInfo, but with zero
      *  dimensions.
      */
     static SkCanvas* NewRaster(const SkImageInfo&);
 
     static SkCanvas* NewRasterN32(int width, int height) {
         return NewRaster(SkImageInfo::MakeN32Premul(width, height));
     }
 
     /**
+     *  Attempt to allocate raster canvas, matching the ImageInfo, that will draw directly into the
+     *  specified pixels. To access the pixels after drawing to them, the caller should call
+     *  flush() or call peekPixels(...).
+     *
+     *  On failure, return NULL. This can fail for several reasons:
+     *  1. invalid ImageInfo (e.g. negative dimensions)
+     *  2. unsupported ImageInfo for a canvas
+     *      - kUnknown_SkColorType, kIndex_8_SkColorType
+     *      - kIgnore_SkAlphaType
+     *      - this list is not complete, so others may also be unsupported
+     *
+     *  Note: it is valid to request a supported ImageInfo, but with zero
+     *  dimensions.
+     */
+    static SkCanvas* NewRasterDirect(const SkImageInfo&, void*, size_t);
+
+    static SkCanvas* NewRasterDirectN32(int width, int height, SkPMColor* pixels, size_t rowBytes) {
+        return NewRasterDirect(SkImageInfo::MakeN32Premul(width, height), pixels, rowBytes);
+    }
+
+    /**
      *  Creates an empty canvas with no backing device/pixels, and zero
      *  dimensions.
      */
     SkCanvas();
 
     /**
      *  Creates a canvas of the specified dimensions, but explicitly not backed
      *  by any device/pixels. Typically this use used by subclasses who handle
      *  the draw calls in some other way.
      */
@@ skipping 1364 matching lines @@
     bool asROBitmap(SkBitmap*) const;
 
 private:
     SkBitmap    fBitmap;    // used if peekPixels() fails
     const void* fAddr;      // NULL on failure
     SkImageInfo fInfo;
     size_t      fRowBytes;
 };
 
 #endif