SkImage_Raster's pixels are always immutable.

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"
 #include "SkDevice.h"
 #include "SkMallocPixelRef.h"
 
 static const size_t kIgnoreRowBytesValue = (size_t)~0;
 
 class SkSurface_Raster : public SkSurface_Base {
 public:
     static bool Valid(const SkImageInfo&, size_t rb = kIgnoreRowBytesValue);
 
     SkSurface_Raster(const SkImageInfo&, void*, size_t rb,
                      void (*releaseProc)(void* pixels, void* context), void* context,
                      const SkSurfaceProps*);
     SkSurface_Raster(SkPixelRef*, const SkSurfaceProps*);
 
     SkCanvas* onNewCanvas() override;
     SkSurface* onNewSurface(const SkImageInfo&) override;
     SkImage* onNewImageSnapshot(Budgeted) override;
     void onDraw(SkCanvas*, SkScalar x, SkScalar y, const SkPaint*) override;
     void onCopyOnWrite(ContentChangeMode) override;
+    void onRestoreBackingMutability() override;
 
 private:
     SkBitmap    fBitmap;
     bool        fWeOwnThePixels;
 
     typedef SkSurface_Base INHERITED;
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
@@ skipping 71 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) {
+    if (fWeOwnThePixels) {
+        // SkImage_raster requires these pixels are immutable for its full lifetime.
+        // We'll undo this via onRestoreBackingMutability() if we can avoid the COW.
+        if (SkPixelRef* pr = fBitmap.pixelRef()) {
+            pr->setTemporarilyImmutable();
+        }
+    }
     // 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);
+    return SkNewImageFromRasterBitmap(fBitmap, &this->props(), kLocked_SharedPixelRefMode,
+                                      fWeOwnThePixels ? kNo_ForceCopyMode : kYes_ForceCopyMode);
+}
+
+void SkSurface_Raster::onRestoreBackingMutability() {
+    SkASSERT(!this->hasCachedImage());  // Shouldn't be any snapshots out there.
+    if (SkPixelRef* pr = fBitmap.pixelRef()) {
+        pr->restoreMutability();
+    }
 }
 
 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 16 matching lines @@
                                                  void* context, const SkSurfaceProps* props) {
     if (NULL == releaseProc) {
         context = NULL;
     }
     if (!SkSurface_Raster::Valid(info, rb)) {
         return NULL;
     }
     if (NULL == pixels) {
         return NULL;
     }
-    
+
     return SkNEW_ARGS(SkSurface_Raster, (info, pixels, rb, releaseProc, context, props));
 }
 
 SkSurface* SkSurface::NewRasterDirect(const SkImageInfo& info, void* pixels, size_t rowBytes,
                                       const SkSurfaceProps* props) {
     return NewRasterDirectReleaseProc(info, pixels, rowBytes, NULL, NULL, props);
 }
 
 SkSurface* SkSurface::NewRaster(const SkImageInfo& info, const SkSurfaceProps* props) {
     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));
 }