Fix painting problem with transparent plugins because plugins were ignoring the alpha channel sometimes.

This change introduces another buffer which holds the background image for transparent plugins.  Before
painting these plugins, their backing store is overwritten with the background data.

This change also uses an ACK from the renderer to figure out when it can paint, similar to how the
renderer does it, which gives us throttling and also doesn't lead to painting when the tab is hidden.


Review URL: http://codereview.chromium.org/5040

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@2744 0039d316-1c4b-4281-b951-d872f2087c98

7 files changed, 300 insertions, 140 deletions

diff --git a/chrome/common/plugin_messages_internal.h b/chrome/common/plugin_messages_internal.h
index 36cb1cd..146cd9c 100644
--- a/chrome/common/plugin_messages_internal.h
+++ b/chrome/common/plugin_messages_internal.h
@@ -102,6 +102,14 @@ IPC_BEGIN_MESSAGES(Plugin, 5)
                              PluginMsg_Init_Params,
                              bool /* result */)
 
+  // Used to synchronously request a paint for windowless plugins.
+  IPC_SYNC_MESSAGE_ROUTED1_0(PluginMsg_Paint,
+                             gfx::Rect /* damaged_rect */)
+
+  // Sent by the renderer after it paints from its backing store so that the
+  // plugin knows it can send more invalidates.
+  IPC_MESSAGE_ROUTED0(PluginMsg_DidPaint)
+
   IPC_SYNC_MESSAGE_ROUTED0_1(PluginMsg_Print,
                              PluginMsg_PrintResponse_Params /* params */)
 
@@ -112,12 +120,16 @@ IPC_BEGIN_MESSAGES(Plugin, 5)
   IPC_SYNC_MESSAGE_ROUTED1_0(PluginMsg_DidFinishLoadWithReason,
                              int /* reason */)
 
+  // Updates the plugin location.  For windowless plugins, windowless_buffer
+  // contains a buffer that the plugin draws into.  background_buffer is used
+  // for transparent windowless plugins, and holds the background of the plugin
+  // rectangle.
   IPC_MESSAGE_ROUTED5(PluginMsg_UpdateGeometry,
                       gfx::Rect /* window_rect */,
                       gfx::Rect /* clip_rect */,
                       bool /* visible */,
                       SharedMemoryHandle /* windowless_buffer */,
-                      SharedMemoryLock /* windowless_buffer_lock */)
+                      SharedMemoryHandle /* background_buffer */)
 
   IPC_SYNC_MESSAGE_ROUTED0_0(PluginMsg_SetFocus)
 
@@ -197,8 +209,6 @@ IPC_BEGIN_MESSAGES(PluginHost, 6)
   IPC_SYNC_MESSAGE_ROUTED1_0(PluginHostMsg_CancelResource,
                              int /* id */)
 
-  IPC_MESSAGE_ROUTED0(PluginHostMsg_Invalidate)
-
   IPC_MESSAGE_ROUTED1(PluginHostMsg_InvalidateRect,
                       gfx::Rect /* rect */)
 
diff --git a/chrome/plugin/webplugin_delegate_stub.cc b/chrome/plugin/webplugin_delegate_stub.cc
index e2129f2..84bc069 100644
--- a/chrome/plugin/webplugin_delegate_stub.cc
+++ b/chrome/plugin/webplugin_delegate_stub.cc
@@ -80,6 +80,8 @@ void WebPluginDelegateStub::OnMessageReceived(const IPC::Message& msg) {
                         OnDidFinishLoadWithReason)
     IPC_MESSAGE_HANDLER(PluginMsg_SetFocus, OnSetFocus)
     IPC_MESSAGE_HANDLER(PluginMsg_HandleEvent, OnHandleEvent)
+    IPC_MESSAGE_HANDLER(PluginMsg_Paint, OnPaint)    
+    IPC_MESSAGE_HANDLER(PluginMsg_DidPaint, OnDidPaint)    
     IPC_MESSAGE_HANDLER(PluginMsg_Print, OnPrint)
     IPC_MESSAGE_HANDLER(PluginMsg_GetPluginScriptableObject,
                         OnGetPluginScriptableObject)
@@ -199,6 +201,14 @@ void WebPluginDelegateStub::OnHandleEvent(const NPEvent& event,
   *handled = delegate_->HandleEvent(const_cast<NPEvent*>(&event), cursor);
 }
 
+void WebPluginDelegateStub::OnPaint(const gfx::Rect& damaged_rect) {
+  webplugin_->Paint(damaged_rect);
+}
+
+void WebPluginDelegateStub::OnDidPaint() {
+  webplugin_->DidPaint();
+}
+
 void WebPluginDelegateStub::OnPrint(PluginMsg_PrintResponse_Params* params) {
   gfx::Emf emf;
   if (!emf.CreateDc(NULL, NULL)) {
@@ -229,9 +239,9 @@ void WebPluginDelegateStub::OnUpdateGeometry(
     const gfx::Rect& clip_rect,
     bool visible,
     const SharedMemoryHandle& windowless_buffer,
-    const SharedMemoryLock& lock) {
+    const SharedMemoryHandle& background_buffer) {
   webplugin_->UpdateGeometry(
-      window_rect, clip_rect, visible, windowless_buffer, lock);
+      window_rect, clip_rect, visible, windowless_buffer, background_buffer);
 }
 
 void WebPluginDelegateStub::OnGetPluginScriptableObject(int* route_id,
diff --git a/chrome/plugin/webplugin_delegate_stub.h b/chrome/plugin/webplugin_delegate_stub.h
index cb242b4..78684bf 100644
--- a/chrome/plugin/webplugin_delegate_stub.h
+++ b/chrome/plugin/webplugin_delegate_stub.h
@@ -57,11 +57,16 @@ class WebPluginDelegateStub : public IPC::Channel::Listener,
   void OnSetFocus();
   void OnHandleEvent(const NPEvent& event, bool* handled,
                      WebCursor* cursor);
+
+  void OnPaint(const gfx::Rect& damaged_rect);
+  void OnDidPaint();
+
   void OnPrint(PluginMsg_PrintResponse_Params* params);
+
   void OnUpdateGeometry(const gfx::Rect& window_rect,
                         const gfx::Rect& clip_rect, bool visible,
                         const SharedMemoryHandle& windowless_buffer,
-                        const SharedMemoryLock& lock);
+                        const SharedMemoryHandle& background_buffer);
   void OnGetPluginScriptableObject(int* route_id, void** npobject_ptr);
   void OnSendJavaScriptStream(const std::string& url,
                               const std::wstring& result,
diff --git a/chrome/plugin/webplugin_proxy.cc b/chrome/plugin/webplugin_proxy.cc
index cc091a2..2abafb0 100644
--- a/chrome/plugin/webplugin_proxy.cc
+++ b/chrome/plugin/webplugin_proxy.cc
@@ -18,9 +18,6 @@
 #include "chrome/plugin/npobject_util.h"
 #include "webkit/glue/plugins/webplugin_delegate_impl.h"
 
-// How many times per second we draw windowless plugins.
-static const int kWindowlessPaintFPS = 30;
-
 typedef std::map<CPBrowsingContext, WebPluginProxy*> ContextMap;
 static ContextMap& GetContextMap() {
   return *Singleton<ContextMap>::get();
@@ -36,7 +33,8 @@ WebPluginProxy::WebPluginProxy(
       cp_browsing_context_(0),
       window_npobject_(NULL),
       plugin_element_(NULL),
-      delegate_(delegate) {
+      delegate_(delegate),
+      waiting_for_paint_(false) {
 
   HANDLE event;
   BOOL result = DuplicateHandle(channel->renderer_handle(),
@@ -81,14 +79,25 @@ void WebPluginProxy::CancelResource(int id) {
 }
 
 void WebPluginProxy::Invalidate() {
-  Send(new PluginHostMsg_Invalidate(route_id_));
+  gfx::Rect rect(0, 0, delegate_->rect().width(), delegate_->rect().height());
+  InvalidateRect(rect);
 }
 
 void WebPluginProxy::InvalidateRect(const gfx::Rect& rect) {
+  // Ignore NPN_InvalidateRect calls with empty rects.
+  if (rect.IsEmpty())
+    return;
+
   damaged_rect_ = damaged_rect_.Union(rect);
-  if (!paint_timer_.IsRunning()) {
-    paint_timer_.Start(TimeDelta::FromMilliseconds(1000 / kWindowlessPaintFPS),
-                      this, &WebPluginProxy::OnPaintTimerFired);
+  // Only send a single InvalidateRect message at a time.  From DidPaint we
+  // will dispatch an additional InvalidateRect message if necessary.
+  if (!waiting_for_paint_) {
+    waiting_for_paint_ = true;
+    // Paint to the plugin bitmap and let the renderer know so it can update
+    // its backing store.
+    Paint(damaged_rect_);
+    Send(new PluginHostMsg_InvalidateRect(route_id_, damaged_rect_));
+    damaged_rect_ = gfx::Rect();
   }
 }
 
@@ -190,6 +199,14 @@ WebPluginResourceClient* WebPluginProxy::GetResourceClient(int id) {
   return iterator->second;
 }
 
+void WebPluginProxy::DidPaint() {
+  // If we have an accumulated damaged rect, then check to see if we need to
+  // send out another InvalidateRect message.
+  waiting_for_paint_ = false;
+  if (!damaged_rect_.IsEmpty())
+    InvalidateRect(damaged_rect_);
+}
+
 void WebPluginProxy::OnResourceCreated(int resource_id, HANDLE cookie) {
   WebPluginResourceClient* resource_client =
       reinterpret_cast<WebPluginResourceClient*>(cookie);
@@ -233,33 +250,26 @@ void WebPluginProxy::HandleURLRequest(const char *method,
   Send(new PluginHostMsg_URLRequest(route_id_, params));
 }
 
-void WebPluginProxy::OnPaintTimerFired() {
+void WebPluginProxy::Paint(const gfx::Rect& rect) {
   if (!windowless_hdc_)
     return;
 
-  if (damaged_rect_.IsEmpty()) {
-    paint_timer_.Stop();
-    return;
-  }
-
-  DWORD wait_result = WaitForSingleObject(windowless_buffer_lock_, INFINITE);
-  DCHECK(wait_result == WAIT_OBJECT_0);
-
   // Clear the damaged area so that if the plugin doesn't paint there we won't
   // end up with the old values.
-  gfx::Rect offset_rect = damaged_rect_;
-  offset_rect.Offset(delegate_->rect().x(), delegate_->rect().y());
-  FillRect(windowless_hdc_, &offset_rect.ToRECT(),
-      static_cast<HBRUSH>(GetStockObject(BLACK_BRUSH)));
+  gfx::Rect offset_rect = rect;
+      offset_rect.Offset(delegate_->rect().x(), delegate_->rect().y());
+  if (!background_hdc_) {
+    FillRect(windowless_hdc_, &offset_rect.ToRECT(),
+        static_cast<HBRUSH>(GetStockObject(BLACK_BRUSH)));
+  } else {
+    BitBlt(windowless_hdc_, offset_rect.x(), offset_rect.y(),
+      offset_rect.width(), offset_rect.height(), background_hdc_,
+      rect.x(), rect.y(), SRCCOPY);
+  }
 
   // Before we send the invalidate, paint so that renderer uses the updated
   // bitmap.
-  delegate_->Paint(windowless_hdc_, damaged_rect_);
-  BOOL result = ReleaseMutex(windowless_buffer_lock_);
-  DCHECK(result);
-
-  Send(new PluginHostMsg_InvalidateRect(route_id_, damaged_rect_));
-  damaged_rect_ = gfx::Rect();
+  delegate_->Paint(windowless_hdc_, offset_rect);
 }
 
 void WebPluginProxy::UpdateGeometry(
@@ -267,33 +277,45 @@ void WebPluginProxy::UpdateGeometry(
     const gfx::Rect& clip_rect,
     bool visible,
     const SharedMemoryHandle& windowless_buffer,
-    const SharedMemoryLock& lock) {
+    const SharedMemoryHandle& background_buffer) {
+      gfx::Rect old = delegate_->rect();
   bool moved = delegate_->rect().x() != window_rect.x() ||
                delegate_->rect().y() != window_rect.y();
   delegate_->UpdateGeometry(window_rect, clip_rect, visible);
   if (windowless_buffer) {
     // The plugin's rect changed, so now we have a new buffer to draw into.
-    SetWindowlessBuffer(windowless_buffer, lock);
+    SetWindowlessBuffer(windowless_buffer, background_buffer);
   } else if (moved) {
     // The plugin moved, so update our world transform.
     UpdateTransform();
   }
 }
 
-void WebPluginProxy::SetWindowlessBuffer(const SharedMemoryHandle& handle,
-                                         const SharedMemoryLock& lock) {
+void WebPluginProxy::SetWindowlessBuffer(
+    const SharedMemoryHandle& windowless_buffer,
+    const SharedMemoryHandle& background_buffer) {
   // Convert the shared memory handle to a handle that works in our process,
   // and then use that to create an HDC.
-  windowless_shared_section_.Set(win_util::GetSectionFromProcess(
-      handle, channel_->renderer_handle(), false));
-  if (!windowless_buffer_lock_) {
-    HANDLE dup_handle = NULL;
-    DuplicateHandle(channel_->renderer_handle(), lock, GetCurrentProcess(),
-                    &dup_handle, 0, FALSE, DUPLICATE_SAME_ACCESS);
-    windowless_buffer_lock_.Set(dup_handle);
+  ConvertBuffer(windowless_buffer,
+                &windowless_shared_section_,
+                &windowless_bitmap_,
+                &windowless_hdc_);
+  if (background_buffer) {
+    ConvertBuffer(background_buffer,
+                  &background_shared_section_,
+                  &background_bitmap_,
+                  &background_hdc_);
   }
+  UpdateTransform();
+}
 
-  if (windowless_shared_section_ == NULL || windowless_buffer_lock_ == NULL) {
+void WebPluginProxy::ConvertBuffer(const SharedMemoryHandle& buffer,
+                                   ScopedHandle* shared_section,
+                                   ScopedBitmap* bitmap,
+                                   ScopedHDC* hdc) {
+  shared_section->Set(win_util::GetSectionFromProcess(
+      buffer, channel_->renderer_handle(), false));
+  if (shared_section->Get() == NULL) {
     NOTREACHED();
     return;
   }
@@ -304,24 +326,23 @@ void WebPluginProxy::SetWindowlessBuffer(const SharedMemoryHandle& handle,
   gfx::CreateBitmapHeader(delegate_->rect().width(),
                           delegate_->rect().height(),
                           &bitmap_header);
-  windowless_bitmap_.Set(CreateDIBSection(
+  bitmap->Set(CreateDIBSection(
       screen_dc, reinterpret_cast<const BITMAPINFO*>(&bitmap_header),
-      DIB_RGB_COLORS, &data, windowless_shared_section_, 0));
+      DIB_RGB_COLORS, &data, shared_section->Get(), 0));
   ReleaseDC(NULL, screen_dc);
-  if (windowless_bitmap_ == NULL) {
+  if (bitmap->Get() == NULL) {
     NOTREACHED();
     return;
   }
 
-  windowless_hdc_.Set(CreateCompatibleDC(NULL));
-  if (windowless_hdc_ == NULL) {
+  hdc->Set(CreateCompatibleDC(NULL));
+  if (hdc->Get() == NULL) {
     NOTREACHED();
     return;
   }
 
-  gfx::PlatformDeviceWin::InitializeDC(windowless_hdc_);
-  SelectObject(windowless_hdc_, windowless_bitmap_);
-  UpdateTransform();
+  gfx::PlatformDeviceWin::InitializeDC(hdc->Get());
+  SelectObject(hdc->Get(), bitmap->Get());
 }
 
 void WebPluginProxy::UpdateTransform() {
diff --git a/chrome/plugin/webplugin_proxy.h b/chrome/plugin/webplugin_proxy.h
index 9e1a051..ab50933 100644
--- a/chrome/plugin/webplugin_proxy.h
+++ b/chrome/plugin/webplugin_proxy.h
@@ -62,6 +62,12 @@ class WebPluginProxy : public WebPlugin {
   // object with that id exists.
   WebPluginResourceClient* GetResourceClient(int id);
 
+  // For windowless plugins, paints the given rectangle into the local buffer.
+  void Paint(const gfx::Rect& rect);
+
+  // Callback from the renderer to let us know that a paint occurred.
+  void DidPaint();
+
   // Notification received on a plugin issued resource request
   // creation.
   void OnResourceCreated(int resource_id, HANDLE cookie);
@@ -77,7 +83,7 @@ class WebPluginProxy : public WebPlugin {
                       const gfx::Rect& clip_rect,
                       bool visible,
                       const SharedMemoryHandle& windowless_buffer,
-                      const SharedMemoryLock& lock);
+                      const SharedMemoryHandle& background_buffer);
 
   void CancelDocumentLoad();
 
@@ -90,12 +96,16 @@ class WebPluginProxy : public WebPlugin {
  private:
   bool Send(IPC::Message* msg);
 
-  // Called periodically so that we can paint windowless plugins.
-  void OnPaintTimerFired();
-
   // Updates the shared memory section where windowless plugins paint.
-  void SetWindowlessBuffer(const SharedMemoryHandle& handle,
-                           const SharedMemoryLock& lock);
+  void SetWindowlessBuffer(const SharedMemoryHandle& windowless_buffer,
+                           const SharedMemoryHandle& background_buffer);
+
+  // Converts a shared memory section handle from the renderer process into a
+  // bitmap and hdc that are mapped to this process.
+  void ConvertBuffer(const SharedMemoryHandle& buffer,
+                     ScopedHandle* shared_section,
+                     ScopedBitmap* bitmap,
+                     ScopedHDC* hdc);
 
   // Called when a plugin's origin moves, so that we can update the world
   // transform of the local HDC.
@@ -109,20 +119,23 @@ class WebPluginProxy : public WebPlugin {
   NPObject* window_npobject_;
   NPObject* plugin_element_;
   WebPluginDelegateImpl* delegate_;
+  gfx::Rect damaged_rect_;
+  bool waiting_for_paint_;
   uint32 cp_browsing_context_;
   ScopedHandle modal_dialog_event_;
 
-  // Used to desynchronize windowless painting.  We accumulate invalidates and
-  // paint into a shared buffer when our repeating timer fires.  After painting
-  // we tell the renderer asynchronously and it paints from the buffer.  This
-  // allows the renderer to paint without a blocking call, which improves
-  // performance, and lets us control the frame rate at which we paint.
-  gfx::Rect damaged_rect_;
-  base::RepeatingTimer<WebPluginProxy> paint_timer_;
+  // Variables used for desynchronized windowless plugin painting.  See note in
+  // webplugin_delegate_proxy.h for how this works.
+
+  // These hold the bitmap where the plugin draws.
   ScopedHandle windowless_shared_section_;
   ScopedBitmap windowless_bitmap_;
   ScopedHDC windowless_hdc_;
-  ScopedHandle windowless_buffer_lock_;
+
+  // These hold the bitmap of the background image.
+  ScopedHandle background_shared_section_;
+  ScopedBitmap background_bitmap_;
+  ScopedHDC background_hdc_;
 };
 
 #endif  // CHROME_PLUGIN_PLUGIN_WEBPLUGIN_PROXY_H__
diff --git a/chrome/renderer/webplugin_delegate_proxy.cc b/chrome/renderer/webplugin_delegate_proxy.cc
index 5670bf7..1d6e8d21 100644
--- a/chrome/renderer/webplugin_delegate_proxy.cc
+++ b/chrome/renderer/webplugin_delegate_proxy.cc
@@ -143,7 +143,9 @@ WebPluginDelegateProxy::WebPluginDelegateProxy(const std::string& mime_type,
       send_deferred_update_geometry_(false),
       visible_(false),
       sad_plugin_(NULL),
-      window_script_object_(NULL) {
+      window_script_object_(NULL),
+      transparent_(false),
+      invalidate_pending_(false) {
 }
 
 WebPluginDelegateProxy::~WebPluginDelegateProxy() {
@@ -222,6 +224,11 @@ bool WebPluginDelegateProxy::Initialize(const GURL& url, char** argn,
   for (int i = 0; i < argc; ++i) {
     params.arg_names.push_back(argn[i]);
     params.arg_values.push_back(argv[i]);
+
+    if (LowerCaseEqualsASCII(params.arg_names.back(), "wmode") &&
+        LowerCaseEqualsASCII(params.arg_values.back(), "transparent")) {
+      transparent_ = true;
+    }
   }
   params.load_manually = load_manually;
   params.modal_dialog_event = render_view_->modal_dialog_event();
@@ -299,7 +306,6 @@ void WebPluginDelegateProxy::OnMessageReceived(const IPC::Message& msg) {
   IPC_BEGIN_MESSAGE_MAP(WebPluginDelegateProxy, msg)
     IPC_MESSAGE_HANDLER(PluginHostMsg_SetWindow, OnSetWindow)
     IPC_MESSAGE_HANDLER(PluginHostMsg_CancelResource, OnCancelResource)
-    IPC_MESSAGE_HANDLER(PluginHostMsg_Invalidate, OnInvalidate)
     IPC_MESSAGE_HANDLER(PluginHostMsg_InvalidateRect, OnInvalidateRect)
     IPC_MESSAGE_HANDLER(PluginHostMsg_GetWindowScriptNPObject,
                         OnGetWindowScriptNPObject)
@@ -322,21 +328,14 @@ void WebPluginDelegateProxy::OnMessageReceived(const IPC::Message& msg) {
 }
 
 void WebPluginDelegateProxy::OnChannelError() {
-  OnInvalidate();
+  if (plugin_)
+    plugin_->Invalidate();
   render_view_->PluginCrashed(plugin_path_);
 }
 
-// Copied from render_widget.cc
-static size_t GetPaintBufSize(const gfx::Rect& rect) {
-  // TODO(darin): protect against overflow
-  return 4 * rect.width() * rect.height();
-}
-
 void WebPluginDelegateProxy::UpdateGeometry(const gfx::Rect& window_rect,
                                             const gfx::Rect& clip_rect,
                                             bool visible) {
-  bool moved = plugin_rect_.x() != window_rect.x() ||
-               plugin_rect_.y() != window_rect.y();
   plugin_rect_ = window_rect;
   if (!windowless_) {
     deferred_clip_rect_ = clip_rect;
@@ -345,43 +344,65 @@ void WebPluginDelegateProxy::UpdateGeometry(const gfx::Rect& window_rect,
     return;
   }
 
-  HANDLE windowless_buffer_handle = NULL;
-  if (!windowless_canvas_.get() ||
-      (window_rect.width() != windowless_canvas_->getDevice()->width() ||
-       window_rect.height() != windowless_canvas_->getDevice()->height())) {
-    // Create a shared memory section that the plugin paints asynchronously.
-    windowless_canvas_.reset();
-    if (!windowless_buffer_lock_)
-      windowless_buffer_lock_.Set(CreateMutex(NULL, FALSE, NULL));
-    windowless_buffer_.reset(new SharedMemory());
-    size_t size = GetPaintBufSize(plugin_rect_);
-    if (!windowless_buffer_->Create(L"", false, true, size)) {
-      DCHECK(false);
-      windowless_buffer_.reset();
-      return;
+  HANDLE transport_store_handle = NULL;
+  HANDLE background_store_handle = NULL;
+  if (!backing_store_canvas_.get() ||
+      (window_rect.width() != backing_store_canvas_->getDevice()->width() ||
+       window_rect.height() != backing_store_canvas_->getDevice()->height())) {
+    // Create a shared memory section that the plugin paints into
+    // asynchronously.
+    ResetWindowlessBitmaps();
+    if (!window_rect.IsEmpty()) {
+      if (!CreateBitmap(&backing_store_, &backing_store_canvas_) ||
+          !CreateBitmap(&transport_store_, &transport_store_canvas_) ||
+          (transparent_ &&
+           !CreateBitmap(&background_store_, &background_store_canvas_))) {
+        DCHECK(false);
+        ResetWindowlessBitmaps();
+        return;
+      }
+
+      transport_store_handle = transport_store_->handle();
+      if (background_store_.get())
+        background_store_handle = background_store_->handle();
     }
-
-    windowless_canvas_.reset(new gfx::PlatformCanvasWin(
-        plugin_rect_.width(), plugin_rect_.height(), false,
-        windowless_buffer_->handle()));
-    windowless_canvas_->translate(static_cast<SkScalar>(-plugin_rect_.x()),
-                                  static_cast<SkScalar>(-plugin_rect_.y()));
-    windowless_canvas_->getTopPlatformDevice().accessBitmap(true).
-        eraseARGB(0, 0, 0, 0);
-    windowless_buffer_handle = windowless_buffer_->handle();
-  } else if (moved) {
-    windowless_canvas_->resetMatrix();
-    windowless_canvas_->translate(static_cast<SkScalar>(-plugin_rect_.x()),
-                                  static_cast<SkScalar>(-plugin_rect_.y()));
   }
 
   IPC::Message* msg = new PluginMsg_UpdateGeometry(
-      instance_id_, window_rect, clip_rect, visible, windowless_buffer_handle,
-      windowless_buffer_lock_);
+      instance_id_, window_rect, clip_rect, visible, transport_store_handle,
+      background_store_handle);
   msg->set_unblock(true);
   Send(msg);
 }
 
+// Copied from render_widget.cc
+static size_t GetPaintBufSize(const gfx::Rect& rect) {
+  // TODO(darin): protect against overflow
+  return 4 * rect.width() * rect.height();
+}
+
+void WebPluginDelegateProxy::ResetWindowlessBitmaps() {
+  backing_store_.reset();
+  transport_store_.reset();
+  backing_store_canvas_.reset();
+  transport_store_canvas_.reset();
+  background_store_.reset();
+  background_store_canvas_.release();
+}
+
+bool WebPluginDelegateProxy::CreateBitmap(
+    scoped_ptr<SharedMemory>* memory,
+    scoped_ptr<gfx::PlatformCanvasWin>* canvas) {
+  size_t size = GetPaintBufSize(plugin_rect_);
+  memory->reset(new SharedMemory());
+  if (!(*memory)->Create(L"", false, true, size))
+    return false;
+
+  canvas->reset(new gfx::PlatformCanvasWin(
+      plugin_rect_.width(), plugin_rect_.height(), true, (*memory)->handle()));
+  return true;
+}
+
 void WebPluginDelegateProxy::Paint(HDC hdc, const gfx::Rect& damaged_rect) {
   // If the plugin is no longer connected (channel crashed) draw a crashed
   // plugin bitmap
@@ -398,32 +419,84 @@ void WebPluginDelegateProxy::Paint(HDC hdc, const gfx::Rect& damaged_rect) {
     // We shall use PrintWindow() to draw the window.
     return;
   }
-  first_paint_ = false;
 
   // We got a paint before the plugin's coordinates, so there's no buffer to
   // copy from.
-  if (!windowless_buffer_.get())
+  if (!backing_store_canvas_.get())
     return;
 
   // Limit the damaged rectangle to whatever is contained inside the plugin
   // rectangle, as that's the rectangle that we'll bitblt to the hdc.
   gfx::Rect rect = damaged_rect.Intersect(plugin_rect_);
 
-  DWORD wait_result = WaitForSingleObject(windowless_buffer_lock_, INFINITE);
-  DCHECK(wait_result == WAIT_OBJECT_0);
+  bool background_changed = false;
+  if (background_store_canvas_.get() && BackgroundChanged(hdc, rect)) {
+    background_changed = true;
+    HDC background_hdc =
+        background_store_canvas_->getTopPlatformDevice().getBitmapDC();
+    BitBlt(background_hdc, rect.x()-plugin_rect_.x(), rect.y()-plugin_rect_.y(),
+        rect.width(), rect.height(), hdc, rect.x(), rect.y(), SRCCOPY);
+  }
+
+  if (first_paint_ || background_changed) {
+    gfx::Rect offset_rect = rect;
+    offset_rect.Offset(-plugin_rect_.x(), -plugin_rect_.y());
+    Send(new PluginMsg_Paint(instance_id_, offset_rect));
+    CopyFromTransportToBacking(offset_rect);
+  }
+
+  first_paint_ = false;
+  HDC backing_hdc = backing_store_canvas_->getTopPlatformDevice().getBitmapDC();
+  BitBlt(hdc, rect.x(), rect.y(), rect.width(), rect.height(), backing_hdc,
+      rect.x()-plugin_rect_.x(), rect.y()-plugin_rect_.y(), SRCCOPY);
+
+  if (invalidate_pending_) {
+    // Only send the PaintAck message if this paint is in response to an 
+    // invalidate from the plugin, since this message acts as an access token
+    // to ensure only one process is using the transport dib at a time.
+    invalidate_pending_ = false;
+    Send(new PluginMsg_DidPaint(instance_id_));
+  }
+}
+
+bool WebPluginDelegateProxy::BackgroundChanged(
+    HDC hdc, 
+    const gfx::Rect& rect) {
+  HBITMAP hbitmap = static_cast<HBITMAP>(GetCurrentObject(hdc, OBJ_BITMAP));
+  if (hbitmap == NULL) {
+    NOTREACHED();
+    return true;
+  }
+
+  BITMAP bitmap = { 0 };
+  int result = GetObject(hbitmap, sizeof(bitmap), &bitmap);
+  if (!result) {
+    NOTREACHED();
+    return true;
+  }
 
-  BLENDFUNCTION m_bf;
-  m_bf.BlendOp = AC_SRC_OVER;
-  m_bf.BlendFlags = 0;
-  m_bf.SourceConstantAlpha = 255;
-  m_bf.AlphaFormat = AC_SRC_ALPHA;
+  XFORM xf;
+  if (!GetWorldTransform(hdc, &xf)) {
+    NOTREACHED();
+    return true;
+  }
 
-  HDC new_hdc = windowless_canvas_->getTopPlatformDevice().getBitmapDC();
-  AlphaBlend(hdc, rect.x(), rect.y(), rect.width(), rect.height(),
-      new_hdc, rect.x(), rect.y(), rect.width(), rect.height(), m_bf);
+  int row_byte_size = rect.width() * (bitmap.bmBitsPixel / 8);
+  for (int y = rect.y(); y < rect.bottom(); y++) {
+    char* hdc_row_start = static_cast<char*>(bitmap.bmBits) +
+        (y + static_cast<int>(xf.eDy)) * bitmap.bmWidthBytes +
+        (rect.x() + static_cast<int>(xf.eDx)) * (bitmap.bmBitsPixel / 8);
+
+    // getAddr32 doesn't use the translation units, so we have to subtract
+    // the plugin origin from the coordinates.
+    uint32_t* canvas_row_start =
+        background_store_canvas_->getDevice()->accessBitmap(true).getAddr32(
+            rect.x() - plugin_rect_.x(), y - plugin_rect_.y());
+    if (memcmp(hdc_row_start, canvas_row_start, row_byte_size) != 0)
+      return true;
+  }
 
-  BOOL result = ReleaseMutex(windowless_buffer_lock_);
-  DCHECK(result);
+  return false;
 }
 
 void WebPluginDelegateProxy::Print(HDC hdc) {
@@ -488,11 +561,6 @@ int WebPluginDelegateProxy::GetProcessId() {
   return channel_host_->peer_pid();
 }
 
-HWND WebPluginDelegateProxy::GetWindowHandle() {
-  NOTREACHED() << "GetWindowHandle can't be called on the proxy.";
-  return NULL;
-}
-
 void WebPluginDelegateProxy::OnSetWindow(
     HWND window, HANDLE modal_loop_pump_messages_event) {
   windowless_ = window == NULL;
@@ -508,14 +576,13 @@ void WebPluginDelegateProxy::OnCancelResource(int id) {
     plugin_->CancelResource(id);
 }
 
-void WebPluginDelegateProxy::OnInvalidate() {
-  if (plugin_)
-    plugin_->Invalidate();
-}
-
 void WebPluginDelegateProxy::OnInvalidateRect(const gfx::Rect& rect) {
-  if (plugin_)
-    plugin_->InvalidateRect(rect);
+  if (!plugin_)
+    return;
+
+  invalidate_pending_ = true;
+  CopyFromTransportToBacking(rect);
+  plugin_->InvalidateRect(rect);
 }
 
 void WebPluginDelegateProxy::OnGetWindowScriptNPObject(
@@ -616,6 +683,18 @@ void WebPluginDelegateProxy::PaintSadPlugin(HDC hdc, const gfx::Rect& rect) {
   return;
 }
 
+void WebPluginDelegateProxy::CopyFromTransportToBacking(const gfx::Rect& rect) {
+  if (!backing_store_canvas_.get())
+    return;
+
+  // Copy the damaged rect from the transport bitmap to the backing store.
+  HDC backing = backing_store_canvas_->getTopPlatformDevice().getBitmapDC();
+  HDC transport = transport_store_canvas_->getTopPlatformDevice().getBitmapDC();
+
+  BitBlt(backing, rect.x(), rect.y(), rect.width(), rect.height(),
+      transport, rect.x(), rect.y(), SRCCOPY);
+}
+
 void WebPluginDelegateProxy::OnHandleURLRequest(
     const PluginHostMsg_URLRequest_Params& params) {
   const char* data = NULL;
diff --git a/chrome/renderer/webplugin_delegate_proxy.h b/chrome/renderer/webplugin_delegate_proxy.h
index c457f90..7a7da77 100644
--- a/chrome/renderer/webplugin_delegate_proxy.h
+++ b/chrome/renderer/webplugin_delegate_proxy.h
@@ -60,7 +60,6 @@ class WebPluginDelegateProxy : public WebPluginDelegate,
   virtual void SetFocus();
   virtual bool HandleEvent(NPEvent* event, WebCursor* cursor);
   virtual int GetProcessId();
-  virtual HWND GetWindowHandle();
 
   // IPC::Channel::Listener implementation:
   virtual void OnMessageReceived(const IPC::Message& msg);
@@ -110,7 +109,6 @@ class WebPluginDelegateProxy : public WebPluginDelegate,
                      bool* result);
   void OnHandleURLRequest(const PluginHostMsg_URLRequest_Params& params);
   void OnCancelResource(int id);
-  void OnInvalidate();
   void OnInvalidateRect(const gfx::Rect& rect);
   void OnGetWindowScriptNPObject(int route_id, bool* success, void** npobject_ptr);
   void OnGetPluginElement(int route_id, bool* success, void** npobject_ptr);
@@ -133,6 +131,20 @@ class WebPluginDelegateProxy : public WebPluginDelegate,
   // Draw a graphic indicating a crashed plugin.
   void PaintSadPlugin(HDC hdc, const gfx::Rect& rect);
 
+  // Returns true if the given rectangle is different in the hdc and the
+  // current background bitmap.
+  bool BackgroundChanged(HDC hdc, const gfx::Rect& rect);
+
+  // Copies the given rectangle from the transport bitmap to the backing store.
+  void CopyFromTransportToBacking(const gfx::Rect& rect);
+
+  // Clears the shared memory section and canvases used for windowless plugins.
+  void ResetWindowlessBitmaps();
+
+  // Creates a shared memory section and canvas.
+  bool CreateBitmap(scoped_ptr<SharedMemory>* memory,
+                    scoped_ptr<gfx::PlatformCanvasWin>* canvas);
+
   RenderView* render_view_;
   WebPlugin* plugin_;
   bool windowless_;
@@ -158,11 +170,21 @@ class WebPluginDelegateProxy : public WebPluginDelegate,
   // Bitmap for crashed plugin
   SkBitmap* sad_plugin_;
 
-  // Used for desynchronized windowless painting.  See the comment in
-  // webplugin_proxy.h for information about how this works.
-  scoped_ptr<SharedMemory> windowless_buffer_;
-  scoped_ptr<gfx::PlatformCanvasWin> windowless_canvas_;
-  ScopedHandle windowless_buffer_lock_;
+  // True if we got an invalidate from the plugin and are waiting for a paint.
+  bool invalidate_pending_;
+
+  // Used to desynchronize windowless painting.  When WebKit paints, we bitblt
+  // from our backing store of what the plugin rectangle looks like.  The
+  // plugin paints into the transport store, and we copy that to our backing
+  // store when we get an invalidate from it.  The background bitmap is used
+  // for transparent plugins, as they need the backgroud data during painting.
+  bool transparent_;
+  scoped_ptr<SharedMemory> backing_store_;
+  scoped_ptr<gfx::PlatformCanvasWin> backing_store_canvas_;
+  scoped_ptr<SharedMemory> transport_store_;
+  scoped_ptr<gfx::PlatformCanvasWin> transport_store_canvas_;
+  scoped_ptr<SharedMemory> background_store_;
+  scoped_ptr<gfx::PlatformCanvasWin> background_store_canvas_;
 
   DISALLOW_EVIL_CONSTRUCTORS(WebPluginDelegateProxy);
 };