support direct writing to top layer

src/core/SkBitmapDevice.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapDevice.h"
 #include "SkConfig8888.h"
 #include "SkDraw.h"
@@ skipping 250 matching lines @@
     SkRasterClip clip(SkIRect::MakeWH(fBitmap.width(), fBitmap.height()));
     SkDraw  draw;
     draw.fRC = &clip;
     draw.fClip = &clip.bwRgn();
     draw.fBitmap = &fBitmap; // canvas should have already called accessBitmap
     draw.fMatrix = &SkMatrix::I();
     this->drawSprite(draw, *sprite, x, y, paint);
 }
 #endif
 
+void* SkBitmapDevice::onAccessPixels(SkImageInfo* info, size_t* rowBytes) {
+    if (fBitmap.getPixels()) {
+        *info = fBitmap.info();
+        *rowBytes = fBitmap.rowBytes();
+        return fBitmap.getPixels();
+    }
+    return NULL;
+}
+
 static void rect_memcpy(void* dst, size_t dstRB, const void* src, size_t srcRB, size_t bytesPerRow,
                         int rowCount) {
     SkASSERT(bytesPerRow <= srcRB);
     SkASSERT(bytesPerRow <= dstRB);
     for (int i = 0; i < rowCount; ++i) {
         memcpy(dst, src, bytesPerRow);
         dst = (char*)dst + dstRB;
         src = (const char*)src + srcRB;
     }
 }
@@ skipping 285 matching lines @@
         paint.getStyle() != SkPaint::kFill_Style ||
         !SkXfermode::IsMode(paint.getXfermode(), SkXfermode::kSrcOver_Mode)) {
         // turn off lcd
         flags->fFlags = paint.getFlags() & ~SkPaint::kLCDRenderText_Flag;
         flags->fHinting = paint.getHinting();
         return true;
     }
     // we're cool with the paint as is
     return false;
 }