cc: Return a NullCanvas instead of NULL in context lost situations.

cc/resources/resource_provider.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/resources/resource_provider.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/containers/hash_tables.h"
 #include "base/debug/trace_event.h"
 #include "base/stl_util.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "cc/base/util.h"
 #include "cc/output/gl_renderer.h"  // For the GLC() macro.
 #include "cc/resources/platform_color.h"
 #include "cc/resources/returned_resource.h"
 #include "cc/resources/shared_bitmap_manager.h"
 #include "cc/resources/texture_uploader.h"
 #include "cc/resources/transferable_resource.h"
 #include "gpu/GLES2/gl2extchromium.h"
 #include "gpu/command_buffer/client/gles2_interface.h"
 #include "third_party/khronos/GLES2/gl2.h"
 #include "third_party/khronos/GLES2/gl2ext.h"
 #include "third_party/skia/include/core/SkSurface.h"
 #include "third_party/skia/include/gpu/GrContext.h"
+#include "third_party/skia/include/utils/SkNullCanvas.h"
 #include "ui/gfx/frame_time.h"
 #include "ui/gfx/rect.h"
 #include "ui/gfx/vector2d.h"
 
 using gpu::gles2::GLES2Interface;
 
 namespace cc {
 
 class IdAllocator {
  public:
@@ skipping 409 matching lines @@
 }
 
 ResourceProvider::GpuRasterBuffer::~GpuRasterBuffer() {
 }
 
 skia::RefPtr<SkCanvas> ResourceProvider::GpuRasterBuffer::AcquireSkCanvas() {
   // Note that this function is called from a worker thread.
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
                "ResourceProvider::GpuRasterBuffer::AcquireSkCanvas");
 
-  return surface_ ? skia::SharePtr(surface_->getCanvas())
-                  : skia::RefPtr<SkCanvas>();
+  skia::RefPtr<SkCanvas> canvas = surface_
+                                      ? skia::SharePtr(surface_->getCanvas())
+                                      : skia::AdoptRef(SkCreateNullCanvas());
+  canvas->save();
+  return canvas;
 }
 
 void ResourceProvider::GpuRasterBuffer::ReleaseSkCanvas(
     const skia::RefPtr<SkCanvas>& canvas) {
   // Note that this function is called from a worker thread.
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
                "ResourceProvider::GpuRasterBuffer::ReleaseSkCanvas");
+
+  canvas->restore();
 }
 
 ResourceProvider::ImageRasterBuffer::ImageRasterBuffer(
     const Resource* resource,
     ResourceProvider* resource_provider)
     : resource_(resource),
       resource_provider_(resource_provider),
       mapped_buffer_(NULL),
       raster_bitmap_changed_(false),
       stride_(0) {
@@ skipping 23 matching lines @@
   }
   return raster_bitmap_changed_;
 }
 
 skia::RefPtr<SkCanvas> ResourceProvider::ImageRasterBuffer::AcquireSkCanvas() {
   // Note that this function is called from a worker thread.
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
                "ResourceProvider::ImageRasterBuffer::AcquireSkCanvas");
 
   if (!mapped_buffer_)
-    return skia::RefPtr<SkCanvas>();
+    return skia::AdoptRef(SkCreateNullCanvas());
 
   MakeBitmap(&raster_bitmap_,
              mapped_buffer_,
              resource_->format,
              resource_->size,
              stride_);
   raster_bitmap_changed_ = true;
   return skia::AdoptRef(new SkCanvas(raster_bitmap_));
 }
 
@@ skipping 43 matching lines @@
   }
   return raster_bitmap_changed_;
 }
 
 skia::RefPtr<SkCanvas> ResourceProvider::PixelRasterBuffer::AcquireSkCanvas() {
   // Note that this function is called from a worker thread.
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
                "ResourceProvider::PixelRasterBuffer::AcquireSkCanvas");
 
   if (!mapped_buffer_)
-    return skia::RefPtr<SkCanvas>();
+    return skia::AdoptRef(SkCreateNullCanvas());
 
   MakeBitmap(&raster_bitmap_,
              mapped_buffer_,
              resource_->format,
              resource_->size,
              stride_);
   raster_bitmap_changed_ = true;
   return skia::AdoptRef(new SkCanvas(raster_bitmap_));
 }
 
@@ skipping 1717 matching lines @@
   ContextProvider* context_provider = output_surface_->context_provider();
   return context_provider ? context_provider->ContextGL() : NULL;
 }
 
 class GrContext* ResourceProvider::GrContext() const {
   ContextProvider* context_provider = output_surface_->context_provider();
   return context_provider ? context_provider->GrContext() : NULL;
 }
 
 }  // namespace cc