Make peekPixels() usable with raster surface snapshots

src/image/SkSurface_Raster.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkSurface_Base.h"
 #include "SkImagePriv.h"
 #include "SkCanvas.h"
@@ skipping 100 matching lines @@
 SkSurface* SkSurface_Raster::onNewSurface(const SkImageInfo& info) {
     return SkSurface::NewRaster(info, &this->props());
 }
 
 void SkSurface_Raster::onDraw(SkCanvas* canvas, SkScalar x, SkScalar y,
                               const SkPaint* paint) {
     canvas->drawBitmap(fBitmap, x, y, paint);
 }
 
 SkImage* SkSurface_Raster::onNewImageSnapshot(Budgeted) {
-    return SkNewImageFromRasterBitmap(fBitmap, fWeOwnThePixels, &this->props());
+    // Our pixels are in memory, so read access on the snapshot SkImage could be cheap.
+    // Lock the shared pixel ref to ensure peekPixels() is usable.
+    return SkNewImageFromRasterBitmap(fBitmap, fWeOwnThePixels, &this->props(),
+                                      kLocked_SharedPixelRefMode);
 }
 
 void SkSurface_Raster::onCopyOnWrite(ContentChangeMode mode) {
     // are we sharing pixelrefs with the image?
     SkASSERT(this->getCachedImage(kNo_Budgeted));
     if (SkBitmapImageGetPixelRef(this->getCachedImage(kNo_Budgeted)) == fBitmap.pixelRef()) {
         SkASSERT(fWeOwnThePixels);
         if (kDiscard_ContentChangeMode == mode) {
             fBitmap.setPixelRef(NULL);
             fBitmap.allocPixels();
@@ skipping 36 matching lines @@
     if (!SkSurface_Raster::Valid(info)) {
         return NULL;
     }
 
     SkAutoTUnref<SkPixelRef> pr(SkMallocPixelRef::NewAllocate(info, 0, NULL));
     if (NULL == pr.get()) {
         return NULL;
     }
     return SkNEW_ARGS(SkSurface_Raster, (pr, props));
 }