Revert 97644 - Unify MacOS resizing path with glResizeCHROMIUM.

Review URL: http://codereview.chromium.org/7671035

TBR=nduca@chromium.org
Review URL: http://codereview.chromium.org/7713001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@97645 0039d316-1c4b-4281-b951-d872f2087c98

10 files changed, 204 insertions, 174 deletions

diff --git a/gpu/command_buffer/build_gles2_cmd_buffer.py b/gpu/command_buffer/build_gles2_cmd_buffer.py
index b09e24a..574897e 100755
--- a/gpu/command_buffer/build_gles2_cmd_buffer.py
+++ b/gpu/command_buffer/build_gles2_cmd_buffer.py
@@ -1727,8 +1727,7 @@ _FUNCTION_INFO = {
                   'GLsizei stride, GLuint offset',
   },
   'ResizeCHROMIUM': {
-      'type': 'Custom',
-      'impl_func': False,
+      'decoder_func': 'DoResizeCHROMIUM',
       'unit_test': False,
       'extension': True,
       'chromium': True,
diff --git a/gpu/command_buffer/client/gles2_implementation.cc b/gpu/command_buffer/client/gles2_implementation.cc
index 956ac62..e34e476 100644
--- a/gpu/command_buffer/client/gles2_implementation.cc
+++ b/gpu/command_buffer/client/gles2_implementation.cc
@@ -2482,12 +2482,6 @@ void GLES2Implementation::UnmapTexSubImage2DCHROMIUM(const void* mem) {
   mapped_textures_.erase(it);
 }
 
-void GLES2Implementation::ResizeCHROMIUM(GLuint width, GLuint height) {
-  GPU_CLIENT_LOG("[" << this << "] glResizeCHROMIUM("
-                 << width << ", " << height << ")");
-  helper_->ResizeCHROMIUM(width, height);
-}
-
 const GLchar* GLES2Implementation::GetRequestableExtensionsCHROMIUM() {
   GPU_CLIENT_LOG("[" << this << "] glGetRequestableExtensionsCHROMIUM()");
   TRACE_EVENT0("gpu",
@@ -2631,3 +2625,4 @@ void GLES2Implementation::GetProgramInfoCHROMIUM(
 
 }  // namespace gles2
 }  // namespace gpu
+
diff --git a/gpu/command_buffer/client/gles2_implementation_autogen.h b/gpu/command_buffer/client/gles2_implementation_autogen.h
index 021e3e9..ba061a5 100644
--- a/gpu/command_buffer/client/gles2_implementation_autogen.h
+++ b/gpu/command_buffer/client/gles2_implementation_autogen.h
@@ -1254,7 +1254,10 @@ void* MapTexSubImage2DCHROMIUM(
 
 void UnmapTexSubImage2DCHROMIUM(const void* mem);
 
-void ResizeCHROMIUM(GLuint width, GLuint height);
+void ResizeCHROMIUM(GLuint width, GLuint height) {
+  GPU_CLIENT_LOG("[" << this << "] glResizeCHROMIUM(" << width << ", " << height << ")");  // NOLINT
+  helper_->ResizeCHROMIUM(width, height);
+}
 
 const GLchar* GetRequestableExtensionsCHROMIUM();
 
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 5e500bb..4f35103 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -468,7 +468,8 @@ class GLES2DecoderImpl : public base::SupportsWeakPtr<GLES2DecoderImpl>,
   virtual void Destroy();
   virtual bool SetParent(GLES2Decoder* parent_decoder,
                          uint32 parent_texture_id);
-  virtual bool ResizeOffscreenFrameBuffer(const gfx::Size& size);
+  virtual void ResizeOffscreenFrameBuffer(const gfx::Size& size);
+  virtual bool UpdateOffscreenFrameBufferSize();
   void UpdateParentTextureInfo();
   virtual bool MakeCurrent();
   virtual GLES2Util* GetGLES2Util() { return &util_; }
@@ -1034,6 +1035,8 @@ class GLES2DecoderImpl : public base::SupportsWeakPtr<GLES2DecoderImpl>,
   // Wrapper for glValidateProgram.
   void DoValidateProgram(GLuint program_client_id);
 
+  void DoResizeCHROMIUM(GLuint width, GLuint height);
+
   void DoSetSurfaceCHROMIUM(GLint surface_id);
 
   // Gets the number of values that will be returned by glGetXXX. Returns
@@ -1178,6 +1181,10 @@ class GLES2DecoderImpl : public base::SupportsWeakPtr<GLES2DecoderImpl>,
   // The parent pointer is reset if the parent is destroyed.
   base::WeakPtr<GLES2DecoderImpl> parent_;
 
+  // Width and height to which an offscreen frame buffer should be resized on
+  // the next call to SwapBuffers.
+  gfx::Size pending_offscreen_size_;
+
   // Current width and height of the offscreen frame buffer.
   gfx::Size offscreen_size_;
 
@@ -1910,7 +1917,8 @@ bool GLES2DecoderImpl::Initialize(
 
     // Allocate the render buffers at their initial size and check the status
     // of the frame buffers is okay.
-    if (!ResizeOffscreenFrameBuffer(size)) {
+    pending_offscreen_size_ = size;
+    if (!UpdateOffscreenFrameBufferSize()) {
       LOG(ERROR) << "Could not allocate offscreen buffer storage.";
       Destroy();
       return false;
@@ -2218,6 +2226,140 @@ GLenum GLES2DecoderImpl::GetBoundDrawFrameBufferInternalFormat() {
   }
 }
 
+bool GLES2DecoderImpl::UpdateOffscreenFrameBufferSize() {
+  if (offscreen_size_ == pending_offscreen_size_)
+    return true;
+
+  offscreen_size_ = pending_offscreen_size_;
+  int w = offscreen_size_.width();
+  int h = offscreen_size_.height();
+  if (w < 0 || h < 0 || h >= (INT_MAX / 4) / (w ? w : 1)) {
+    LOG(ERROR) << "GLES2DecoderImpl::UpdateOffscreenFrameBufferSize failed "
+               << "to allocate storage due to excessive dimensions.";
+    return false;
+  }
+
+  // Reallocate the offscreen target buffers.
+  DCHECK(offscreen_target_color_format_);
+  if (IsOffscreenBufferMultisampled()) {
+    if (!offscreen_target_color_render_buffer_->AllocateStorage(
+        pending_offscreen_size_, offscreen_target_color_format_,
+        offscreen_target_samples_)) {
+      LOG(ERROR) << "GLES2DecoderImpl::UpdateOffscreenFrameBufferSize failed "
+                 << "to allocate storage for offscreen target color buffer.";
+      return false;
+    }
+  } else {
+    if (!offscreen_target_color_texture_->AllocateStorage(
+        pending_offscreen_size_, offscreen_target_color_format_)) {
+      LOG(ERROR) << "GLES2DecoderImpl::UpdateOffscreenFrameBufferSize failed "
+                 << "to allocate storage for offscreen target color texture.";
+      return false;
+    }
+  }
+  if (offscreen_target_depth_format_ &&
+      !offscreen_target_depth_render_buffer_->AllocateStorage(
+      pending_offscreen_size_, offscreen_target_depth_format_,
+      offscreen_target_samples_)) {
+    LOG(ERROR) << "GLES2DecoderImpl::UpdateOffscreenFrameBufferSize failed "
+               << "to allocate storage for offscreen target depth buffer.";
+    return false;
+  }
+  if (offscreen_target_stencil_format_ &&
+      !offscreen_target_stencil_render_buffer_->AllocateStorage(
+      pending_offscreen_size_, offscreen_target_stencil_format_,
+      offscreen_target_samples_)) {
+    LOG(ERROR) << "GLES2DecoderImpl::UpdateOffscreenFrameBufferSize failed "
+               << "to allocate storage for offscreen target stencil buffer.";
+    return false;
+  }
+
+  // Attach the offscreen target buffers to the target frame buffer.
+  if (IsOffscreenBufferMultisampled()) {
+    offscreen_target_frame_buffer_->AttachRenderBuffer(
+        GL_COLOR_ATTACHMENT0,
+        offscreen_target_color_render_buffer_.get());
+  } else {
+    offscreen_target_frame_buffer_->AttachRenderTexture(
+        offscreen_target_color_texture_.get());
+  }
+  if (offscreen_target_depth_format_) {
+    offscreen_target_frame_buffer_->AttachRenderBuffer(
+        GL_DEPTH_ATTACHMENT,
+        offscreen_target_depth_render_buffer_.get());
+  }
+  const bool packed_depth_stencil =
+      offscreen_target_depth_format_ == GL_DEPTH24_STENCIL8;
+  if (packed_depth_stencil) {
+    offscreen_target_frame_buffer_->AttachRenderBuffer(
+        GL_STENCIL_ATTACHMENT,
+        offscreen_target_depth_render_buffer_.get());
+  } else if (offscreen_target_stencil_format_) {
+    offscreen_target_frame_buffer_->AttachRenderBuffer(
+        GL_STENCIL_ATTACHMENT,
+        offscreen_target_stencil_render_buffer_.get());
+  }
+
+  if (offscreen_target_frame_buffer_->CheckStatus() !=
+      GL_FRAMEBUFFER_COMPLETE) {
+      LOG(ERROR) << "GLES2DecoderImpl::UpdateOffscreenFrameBufferSize failed "
+                 << "because offscreen FBO was incomplete.";
+    return false;
+  }
+
+  // Clear the target frame buffer.
+  {
+    ScopedFrameBufferBinder binder(this, offscreen_target_frame_buffer_->id());
+    glClearColor(0, 0, 0, (GLES2Util::GetChannelsForFormat(
+        offscreen_target_color_format_) & 0x0008) != 0 ? 0 : 1);
+    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
+    glClearStencil(0);
+    glStencilMaskSeparate(GL_FRONT, -1);
+    glStencilMaskSeparate(GL_BACK, -1);
+    glClearDepth(0);
+    glDepthMask(GL_TRUE);
+    glDisable(GL_SCISSOR_TEST);
+    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
+    RestoreClearState();
+  }
+
+  // Allocate the offscreen saved color texture.
+  DCHECK(offscreen_saved_color_format_);
+  offscreen_saved_color_texture_->AllocateStorage(
+      pending_offscreen_size_, offscreen_saved_color_format_);
+
+  offscreen_saved_frame_buffer_->AttachRenderTexture(
+      offscreen_saved_color_texture_.get());
+  if (offscreen_saved_frame_buffer_->CheckStatus() !=
+      GL_FRAMEBUFFER_COMPLETE) {
+    LOG(ERROR) << "GLES2DecoderImpl::UpdateOffscreenFrameBufferSize failed "
+               << "because offscreen saved FBO was incomplete.";
+    return false;
+  }
+
+  // Destroy the offscreen resolved framebuffers.
+  if (offscreen_resolved_frame_buffer_.get())
+    offscreen_resolved_frame_buffer_->Destroy();
+  if (offscreen_resolved_color_texture_.get())
+    offscreen_resolved_color_texture_->Destroy();
+  offscreen_resolved_color_texture_.reset();
+  offscreen_resolved_frame_buffer_.reset();
+
+  // Clear the offscreen color texture.
+  {
+    ScopedFrameBufferBinder binder(this, offscreen_saved_frame_buffer_->id());
+    glClearColor(0, 0, 0, 0);
+    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
+    glDisable(GL_SCISSOR_TEST);
+    glClear(GL_COLOR_BUFFER_BIT);
+    RestoreClearState();
+  }
+
+  UpdateParentTextureInfo();
+
+  return true;
+}
+
 void GLES2DecoderImpl::UpdateParentTextureInfo() {
   if (parent_) {
     // Update the info about the offscreen saved color texture in the parent.
@@ -2236,8 +2378,8 @@ void GLES2DecoderImpl::UpdateParentTextureInfo() {
         GL_TEXTURE_2D,
         0,  // level
         GL_RGBA,
-        offscreen_size_.width(),
-        offscreen_size_.height(),
+        pending_offscreen_size_.width(),
+        pending_offscreen_size_.height(),
         1,  // depth
         0,  // border
         GL_RGBA,
@@ -2265,8 +2407,7 @@ void GLES2DecoderImpl::UpdateParentTextureInfo() {
   }
 }
 
-void GLES2DecoderImpl::SetResizeCallback(
-    Callback1<gfx::Size>::Type* callback) {
+void GLES2DecoderImpl::SetResizeCallback(Callback1<gfx::Size>::Type* callback) {
   resize_callback_.reset(callback);
 }
 
@@ -2412,166 +2553,22 @@ bool GLES2DecoderImpl::SetParent(GLES2Decoder* new_parent,
   return true;
 }
 
-bool GLES2DecoderImpl::ResizeOffscreenFrameBuffer(const gfx::Size& size) {
-  bool is_offscreen = !!offscreen_target_frame_buffer_.get();
-  if (!is_offscreen) {
-    LOG(ERROR) << "GLES2DecoderImpl::ResizeOffscreenFrameBuffer called "
-               << " with an onscreen framebuffer.";
-    return false;
-  }
-
-  if (offscreen_size_ == size)
-    return true;
-
-  offscreen_size_ = size;
-  int w = offscreen_size_.width();
-  int h = offscreen_size_.height();
-  if (w < 0 || h < 0 || h >= (INT_MAX / 4) / (w ? w : 1)) {
-    LOG(ERROR) << "GLES2DecoderImpl::ResizeOffscreenFrameBuffer failed "
-               << "to allocate storage due to excessive dimensions.";
-    return false;
-  }
-
-  // Reallocate the offscreen target buffers.
-  DCHECK(offscreen_target_color_format_);
-  if (IsOffscreenBufferMultisampled()) {
-    if (!offscreen_target_color_render_buffer_->AllocateStorage(
-        offscreen_size_, offscreen_target_color_format_,
-        offscreen_target_samples_)) {
-      LOG(ERROR) << "GLES2DecoderImpl::ResizeOffscreenFrameBuffer failed "
-                 << "to allocate storage for offscreen target color buffer.";
-      return false;
-    }
-  } else {
-    if (!offscreen_target_color_texture_->AllocateStorage(
-        offscreen_size_, offscreen_target_color_format_)) {
-      LOG(ERROR) << "GLES2DecoderImpl::ResizeOffscreenFrameBuffer failed "
-                 << "to allocate storage for offscreen target color texture.";
-      return false;
-    }
-  }
-  if (offscreen_target_depth_format_ &&
-      !offscreen_target_depth_render_buffer_->AllocateStorage(
-      offscreen_size_, offscreen_target_depth_format_,
-      offscreen_target_samples_)) {
-    LOG(ERROR) << "GLES2DecoderImpl::ResizeOffscreenFrameBuffer failed "
-               << "to allocate storage for offscreen target depth buffer.";
-    return false;
-  }
-  if (offscreen_target_stencil_format_ &&
-      !offscreen_target_stencil_render_buffer_->AllocateStorage(
-      offscreen_size_, offscreen_target_stencil_format_,
-      offscreen_target_samples_)) {
-    LOG(ERROR) << "GLES2DecoderImpl::ResizeOffscreenFrameBuffer failed "
-               << "to allocate storage for offscreen target stencil buffer.";
-    return false;
-  }
-
-  // Attach the offscreen target buffers to the target frame buffer.
-  if (IsOffscreenBufferMultisampled()) {
-    offscreen_target_frame_buffer_->AttachRenderBuffer(
-        GL_COLOR_ATTACHMENT0,
-        offscreen_target_color_render_buffer_.get());
-  } else {
-    offscreen_target_frame_buffer_->AttachRenderTexture(
-        offscreen_target_color_texture_.get());
-  }
-  if (offscreen_target_depth_format_) {
-    offscreen_target_frame_buffer_->AttachRenderBuffer(
-        GL_DEPTH_ATTACHMENT,
-        offscreen_target_depth_render_buffer_.get());
-  }
-  const bool packed_depth_stencil =
-      offscreen_target_depth_format_ == GL_DEPTH24_STENCIL8;
-  if (packed_depth_stencil) {
-    offscreen_target_frame_buffer_->AttachRenderBuffer(
-        GL_STENCIL_ATTACHMENT,
-        offscreen_target_depth_render_buffer_.get());
-  } else if (offscreen_target_stencil_format_) {
-    offscreen_target_frame_buffer_->AttachRenderBuffer(
-        GL_STENCIL_ATTACHMENT,
-        offscreen_target_stencil_render_buffer_.get());
-  }
-
-  if (offscreen_target_frame_buffer_->CheckStatus() !=
-      GL_FRAMEBUFFER_COMPLETE) {
-      LOG(ERROR) << "GLES2DecoderImpl::ResizeOffscreenFrameBuffer failed "
-                 << "because offscreen FBO was incomplete.";
-    return false;
-  }
-
-  // Clear the target frame buffer.
-  {
-    ScopedFrameBufferBinder binder(this, offscreen_target_frame_buffer_->id());
-    glClearColor(0, 0, 0, (GLES2Util::GetChannelsForFormat(
-        offscreen_target_color_format_) & 0x0008) != 0 ? 0 : 1);
-    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
-    glClearStencil(0);
-    glStencilMaskSeparate(GL_FRONT, -1);
-    glStencilMaskSeparate(GL_BACK, -1);
-    glClearDepth(0);
-    glDepthMask(GL_TRUE);
-    glDisable(GL_SCISSOR_TEST);
-    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
-    RestoreClearState();
-  }
-
-  // Allocate the offscreen saved color texture.
-  DCHECK(offscreen_saved_color_format_);
-  offscreen_saved_color_texture_->AllocateStorage(
-      offscreen_size_, offscreen_saved_color_format_);
-
-  offscreen_saved_frame_buffer_->AttachRenderTexture(
-      offscreen_saved_color_texture_.get());
-  if (offscreen_saved_frame_buffer_->CheckStatus() !=
-      GL_FRAMEBUFFER_COMPLETE) {
-    LOG(ERROR) << "GLES2DecoderImpl::ResizeOffscreenFrameBuffer failed "
-               << "because offscreen saved FBO was incomplete.";
-    return false;
-  }
-
-  // Destroy the offscreen resolved framebuffers.
-  if (offscreen_resolved_frame_buffer_.get())
-    offscreen_resolved_frame_buffer_->Destroy();
-  if (offscreen_resolved_color_texture_.get())
-    offscreen_resolved_color_texture_->Destroy();
-  offscreen_resolved_color_texture_.reset();
-  offscreen_resolved_frame_buffer_.reset();
-
-  // Clear the offscreen color texture.
-  {
-    ScopedFrameBufferBinder binder(this, offscreen_saved_frame_buffer_->id());
-    glClearColor(0, 0, 0, 0);
-    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
-    glDisable(GL_SCISSOR_TEST);
-    glClear(GL_COLOR_BUFFER_BIT);
-    RestoreClearState();
-  }
-
-  UpdateParentTextureInfo();
-
-  return true;
+void GLES2DecoderImpl::ResizeOffscreenFrameBuffer(const gfx::Size& size) {
+  // We can't resize the render buffers immediately because there might be a
+  // partial frame rendered into them and we don't want the tail end of that
+  // rendered into the reallocated storage. Defer until the next SwapBuffers.
+  pending_offscreen_size_ = size;
 }
 
-error::Error GLES2DecoderImpl::HandleResizeCHROMIUM(
-    uint32 immediate_data_size, const gles2::ResizeCHROMIUM& c) {
-  GLuint width = static_cast<GLuint>(c.width);
-  GLuint height = static_cast<GLuint>(c.height);
-  TRACE_EVENT2("gpu", "glResizeChromium", "width", width, "height", height);
+void GLES2DecoderImpl::DoResizeCHROMIUM(GLuint width, GLuint height) {
 #if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(TOUCH_UI)
   // Make sure that we are done drawing to the back buffer before resizing.
   glFinish();
 #endif
-  bool is_offscreen = !!offscreen_target_frame_buffer_.get();
-  if (is_offscreen) {
-    if (!ResizeOffscreenFrameBuffer(gfx::Size(width, height)))
-      return error::kLostContext;
+  if (resize_callback_.get()) {
+    gfx::Size size(width, height);
+    resize_callback_->Run(size);
   }
-
-  if (resize_callback_.get())
-    resize_callback_->Run(gfx::Size(width, height));
-
-  return error::kNoError;
 }
 
 void GLES2DecoderImpl::DoSetSurfaceCHROMIUM(GLint surface_id) {
@@ -6557,6 +6554,14 @@ error::Error GLES2DecoderImpl::HandleSwapBuffers(
   if (is_offscreen) {
     ScopedGLErrorSuppressor suppressor(this);
 
+    // First check to see if a deferred offscreen render buffer resize is
+    // pending.
+    if (!UpdateOffscreenFrameBufferSize()) {
+      LOG(ERROR) << "Context lost because reallocation of offscreen FBO "
+                 << "failed.";
+      return error::kLostContext;
+    }
+
     if (IsOffscreenBufferMultisampled()) {
       // For multisampled buffers, bind the resolved frame buffer so that
       // callbacks can call ReadPixels or CopyTexImage2D.
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.h b/gpu/command_buffer/service/gles2_cmd_decoder.h
index fc66b3d..23c5e3a 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.h
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.h
@@ -81,7 +81,12 @@ class GLES2Decoder : public CommonDecoder {
                          uint32 parent_texture_id) = 0;
 
   // Resize an offscreen frame buffer.
-  virtual bool ResizeOffscreenFrameBuffer(const gfx::Size& size) = 0;
+  virtual void ResizeOffscreenFrameBuffer(const gfx::Size& size) = 0;
+
+  // Force the offscreen frame buffer's size to be updated. This
+  // usually occurs lazily, during SwapBuffers, but on some platforms
+  // (Mac OS X in particular) it must be done immediately.
+  virtual bool UpdateOffscreenFrameBufferSize() = 0;
 
   // Make this decoder's GL context current.
   virtual bool MakeCurrent() = 0;
@@ -100,8 +105,7 @@ class GLES2Decoder : public CommonDecoder {
 
   // Sets a callback which is called when a glResizeCHROMIUM command
   // is processed.
-  virtual void SetResizeCallback(
-      Callback1<gfx::Size>::Type* callback) = 0;
+  virtual void SetResizeCallback(Callback1<gfx::Size>::Type* callback) = 0;
 
   // Sets a callback which is called when a SwapBuffers command is processed.
   virtual void SetSwapBuffersCallback(Callback0::Type* callback) = 0;
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder_autogen.h b/gpu/command_buffer/service/gles2_cmd_decoder_autogen.h
index 27ef39b..9023cfe 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder_autogen.h
+++ b/gpu/command_buffer/service/gles2_cmd_decoder_autogen.h
@@ -2568,6 +2568,14 @@ error::Error GLES2DecoderImpl::HandleGetMaxValueInBufferCHROMIUM(
   return error::kNoError;
 }
 
+error::Error GLES2DecoderImpl::HandleResizeCHROMIUM(
+    uint32 immediate_data_size, const gles2::ResizeCHROMIUM& c) {
+  GLuint width = static_cast<GLuint>(c.width);
+  GLuint height = static_cast<GLuint>(c.height);
+  DoResizeCHROMIUM(width, height);
+  return error::kNoError;
+}
+
 error::Error GLES2DecoderImpl::HandleSetSurfaceCHROMIUM(
     uint32 immediate_data_size, const gles2::SetSurfaceCHROMIUM& c) {
   GLint surface_id = static_cast<GLint>(c.surface_id);
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder_mock.h b/gpu/command_buffer/service/gles2_cmd_decoder_mock.h
index fa9d43d..13e60bb 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder_mock.h
+++ b/gpu/command_buffer/service/gles2_cmd_decoder_mock.h
@@ -38,7 +38,8 @@ class MockGLES2Decoder : public GLES2Decoder {
                     const std::vector<int32>& attribs));
   MOCK_METHOD0(Destroy, void());
   MOCK_METHOD2(SetParent, bool(GLES2Decoder* parent, uint32 parent_texture_id));
-  MOCK_METHOD1(ResizeOffscreenFrameBuffer, bool(const gfx::Size& size));
+  MOCK_METHOD1(ResizeOffscreenFrameBuffer, void(const gfx::Size& size));
+  MOCK_METHOD0(UpdateOffscreenFrameBufferSize, bool());
   MOCK_METHOD0(MakeCurrent, bool());
   MOCK_METHOD1(GetServiceIdForTesting, uint32(uint32 client_id));
   MOCK_METHOD0(GetGLES2Util, GLES2Util*());
diff --git a/gpu/command_buffer/service/gpu_scheduler.cc b/gpu/command_buffer/service/gpu_scheduler.cc
index 6413cc1..15316ea 100644
--- a/gpu/command_buffer/service/gpu_scheduler.cc
+++ b/gpu/command_buffer/service/gpu_scheduler.cc
@@ -228,8 +228,11 @@ int32 GpuScheduler::GetGetOffset() {
   return parser_->get();
 }
 
-void GpuScheduler::SetResizeCallback(
-    Callback1<gfx::Size>::Type* callback) {
+void GpuScheduler::ResizeOffscreenFrameBuffer(const gfx::Size& size) {
+  decoder_->ResizeOffscreenFrameBuffer(size);
+}
+
+void GpuScheduler::SetResizeCallback(Callback1<gfx::Size>::Type* callback) {
   decoder_->SetResizeCallback(callback);
 }
 
diff --git a/gpu/command_buffer/service/gpu_scheduler.h b/gpu/command_buffer/service/gpu_scheduler.h
index 61c60be..75ccc63 100644
--- a/gpu/command_buffer/service/gpu_scheduler.h
+++ b/gpu/command_buffer/service/gpu_scheduler.h
@@ -98,6 +98,9 @@ class GpuScheduler : public CommandBufferEngine {
   virtual bool SetGetOffset(int32 offset);
   virtual int32 GetGetOffset();
 
+  // Asynchronously resizes an offscreen frame buffer.
+  void ResizeOffscreenFrameBuffer(const gfx::Size& size);
+
 #if defined(OS_MACOSX)
   // To prevent the GPU process from overloading the browser process,
   // we need to track the number of swap buffers calls issued and
diff --git a/gpu/command_buffer/service/gpu_scheduler_mac.cc b/gpu/command_buffer/service/gpu_scheduler_mac.cc
index 2efa9cb..cfa0d5c 100644
--- a/gpu/command_buffer/service/gpu_scheduler_mac.cc
+++ b/gpu/command_buffer/service/gpu_scheduler_mac.cc
@@ -74,12 +74,21 @@ void GpuScheduler::Destroy() {
 }
 
 uint64 GpuScheduler::SetWindowSizeForIOSurface(const gfx::Size& size) {
+  // This is called from an IPC handler, so it's undefined which context is
+  // current. Make sure the right one is.
+  decoder_->GetGLContext()->MakeCurrent(decoder_->GetGLSurface());
+
+  ResizeOffscreenFrameBuffer(size);
+  decoder_->UpdateOffscreenFrameBufferSize();
+
   // Note: The following line changes the current context again.
   return surface_->SetSurfaceSize(size);
 }
 
 TransportDIB::Handle GpuScheduler::SetWindowSizeForTransportDIB(
     const gfx::Size& size) {
+  ResizeOffscreenFrameBuffer(size);
+  decoder_->UpdateOffscreenFrameBufferSize();
   return surface_->SetTransportDIBSize(size);
 }