Dispatches mouse movement messages in posted task to improve dragging smoothness

ui/views/widget/desktop_aura/x11_whole_screen_move_loop.cc

 // Copyright (c) 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 "ui/views/widget/desktop_aura/x11_whole_screen_move_loop.h"
 
 #include <X11/Xlib.h>
 // Get rid of a macro from Xlib.h that conflicts with Aura's RootWindow class.
 #undef RootWindow
 
+#include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "base/message_loop/message_pump_x11.h"
 #include "base/run_loop.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "ui/aura/env.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/aura/window_tree_host.h"
 #include "ui/base/x/x11_util.h"
 #include "ui/events/event.h"
@@ skipping 29 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(ScopedCapturer);
 };
 
 }  // namespace
 
 X11WholeScreenMoveLoop::X11WholeScreenMoveLoop(
     X11WholeScreenMoveLoopDelegate* delegate)
     : delegate_(delegate),
       in_move_loop_(false),
       should_reset_mouse_flags_(false),
-      grab_input_window_(None) {
+      grab_input_window_(None),
+      weak_factory_(this) {
+  last_xmotion_.type = LASTEvent;
 }
 
 X11WholeScreenMoveLoop::~X11WholeScreenMoveLoop() {}
 
 ////////////////////////////////////////////////////////////////////////////////
 // DesktopWindowTreeHostLinux, MessagePumpDispatcher implementation:
 
+void X11WholeScreenMoveLoop::DispatchMouseMovement() {
+  if (!weak_factory_.HasWeakPtrs())
+    return;
+  weak_factory_.InvalidateWeakPtrs();
+  DCHECK_EQ(MotionNotify, last_xmotion_.type);
+  delegate_->OnMouseMovement(&last_xmotion_);
+  last_xmotion_.type = LASTEvent;
+}
+
 uint32_t X11WholeScreenMoveLoop::Dispatch(const base::NativeEvent& event) {
   XEvent* xev = event;
 
   // Note: the escape key is handled in the tab drag controller, which has
   // keyboard focus even though we took pointer grab.
   switch (xev->type) {
     case MotionNotify: {
       if (drag_widget_.get()) {
         gfx::Screen* screen = gfx::Screen::GetNativeScreen();
         gfx::Point location = gfx::ToFlooredPoint(
             screen->GetCursorScreenPoint() - drag_offset_);
         drag_widget_->SetBounds(gfx::Rect(location, drag_image_.size()));
         drag_widget_->StackAtTop();
       }
-      delegate_->OnMouseMovement(&xev->xmotion);
+      last_xmotion_ = xev->xmotion;
+      if (!weak_factory_.HasWeakPtrs()) {
+        // Post a task to dispatch mouse movement event when control returns to
+        // the message loop. This allows smoother dragging since the events are
+        // dispatched without waiting for the drag widget updates.
+        base::MessageLoopForUI::current()->PostTask(
+            FROM_HERE,
+            base::Bind(&X11WholeScreenMoveLoop::DispatchMouseMovement,
+                       weak_factory_.GetWeakPtr()));
+      }
       break;
     }
     case ButtonRelease: {
       if (xev->xbutton.button == Button1) {
         // Assume that drags are being done with the left mouse button. Only
         // break the drag if the left mouse button was released.
+        DispatchMouseMovement();
         delegate_->OnMouseReleased();
       }
       break;
     }
     case KeyPress: {
       if (ui::KeyboardCodeFromXKeyEvent(xev) == ui::VKEY_ESCAPE)
         EndMoveLoop();
       break;
     }
   }
@@ skipping 57 matching lines @@
     // cursor. Note: we can be called from handling an XdndStatus message after
     // EndMoveLoop() was called, but before we return from the nested RunLoop.
     GrabPointerAndKeyboard(cursor);
   }
 }
 
 void X11WholeScreenMoveLoop::EndMoveLoop() {
   if (!in_move_loop_)
     return;
 
+  // Prevent DispatchMouseMovement from dispatching any posted motion event.
+  weak_factory_.InvalidateWeakPtrs();
+  last_xmotion_.type = LASTEvent;
+
   // We undo our emulated mouse click from RunMoveLoop();
   if (should_reset_mouse_flags_) {
     aura::Env::GetInstance()->set_mouse_button_flags(0);
     should_reset_mouse_flags_ = false;
   }
 
   // TODO(erg): Is this ungrab the cause of having to click to give input focus
   // on drawn out windows? Not ungrabbing here screws the X server until I kill
   // the chrome process.
 
@@ skipping 126 matching lines @@
     for (int x = 0; x < in_bitmap->width(); ++x) {
       if (SkColorGetA(in_row[x]) > kMinAlpha)
         return true;
     }
   }
 
   return false;
 }
 
 }  // namespace views