ScreenWin notifies DisplayObserver's when displays changed.

ui/gfx/screen_win.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/gfx/screen_win.h"
 
 #include <windows.h>
 
 #include "base/hash.h"
 #include "base/logging.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/win/win_util.h"
 #include "ui/gfx/display.h"
 #include "ui/gfx/win/dpi.h"
 
 namespace {
 
+// The delay to handle the display changes notifications.
+// See comments in ScreenWin::OnDisplayChanged.
+const int64 kConfigureDelayMs = 500;
+
 MONITORINFOEX GetMonitorInfoForMonitor(HMONITOR monitor) {
   MONITORINFOEX monitor_info;
   ZeroMemory(&monitor_info, sizeof(MONITORINFOEX));
   monitor_info.cbSize = sizeof(monitor_info);
   GetMonitorInfo(monitor, &monitor_info);
   return monitor_info;
 }
 
 gfx::Display GetDisplay(MONITORINFOEX& monitor_info) {
-  // TODO(oshima): Implement Observer.
   int64 id = static_cast<int64>(
       base::Hash(base::WideToUTF8(monitor_info.szDevice)));
   gfx::Rect bounds = gfx::Rect(monitor_info.rcMonitor);
   gfx::Display display(id, bounds);
   display.set_work_area(gfx::Rect(monitor_info.rcWork));
   display.SetScaleAndBounds(gfx::win::GetDeviceScaleFactor(), bounds);
 
   DEVMODE mode;
   memset(&mode, 0, sizeof(DEVMODE));
   mode.dmSize = sizeof(DEVMODE);
@@ skipping 34 matching lines @@
   gfx::Display display = GetDisplay(monitor_info);
   all_displays->push_back(display);
   return TRUE;
 }
 
 }  // namespace
 
 namespace gfx {
 
 ScreenWin::ScreenWin() {
+  displays_ = BuildDisplays();
 }
 
 ScreenWin::~ScreenWin() {
 }
 
 bool ScreenWin::IsDIPEnabled() {
   return IsInHighDPIMode();
 }
 
 gfx::Point ScreenWin::GetCursorScreenPoint() {
@@ skipping 12 matching lines @@
 gfx::NativeWindow ScreenWin::GetWindowAtScreenPoint(const gfx::Point& point) {
   gfx::Point point_in_pixels = gfx::win::DIPToScreenPoint(point);
   return GetNativeWindowFromHWND(WindowFromPoint(point_in_pixels.ToPOINT()));
 }
 
 int ScreenWin::GetNumDisplays() const {
   return GetSystemMetrics(SM_CMONITORS);
 }
 
 std::vector<gfx::Display> ScreenWin::GetAllDisplays() const {
-  std::vector<gfx::Display> all_displays;
-  EnumDisplayMonitors(NULL, NULL, EnumMonitorCallback,
-                      reinterpret_cast<LPARAM>(&all_displays));
-  return all_displays;
+  return displays_;
 }
 
 gfx::Display ScreenWin::GetDisplayNearestWindow(gfx::NativeView window) const {
   HWND window_hwnd = GetHWNDFromNativeView(window);
   if (!window_hwnd) {
     // When |window| isn't rooted to a display, we should just return the
     // default display so we get some correct display information like the
     // scaling factor.
     return GetPrimaryDisplay();
   }
@@ skipping 31 matching lines @@
   // TODO(kevers|girard): Test if these checks can be reintroduced for high-DIP
   // once more of the app is DIP-aware.
   if (!(IsInHighDPIMode() || IsHighDPIEnabled())) {
     DCHECK_EQ(GetSystemMetrics(SM_CXSCREEN), display.size().width());
     DCHECK_EQ(GetSystemMetrics(SM_CYSCREEN), display.size().height());
   }
   return display;
 }
 
 void ScreenWin::AddObserver(DisplayObserver* observer) {
-  // TODO(oshima): crbug.com/122863.
+  change_notifier_.AddObserver(observer);
 }
 
 void ScreenWin::RemoveObserver(DisplayObserver* observer) {
-  // TODO(oshima): crbug.com/122863.
+  change_notifier_.RemoveObserver(observer);
 }
 
 HWND ScreenWin::GetHWNDFromNativeView(NativeView window) const {
   NOTREACHED();
   return NULL;
 }
 
 NativeWindow ScreenWin::GetNativeWindowFromHWND(HWND hwnd) const {
   NOTREACHED();
   return NULL;
 }
 
+std::vector<gfx::Display> ScreenWin::BuildDisplays() const {
+  std::vector<gfx::Display> all_displays;
+  EnumDisplayMonitors(NULL, NULL, EnumMonitorCallback,
+                      reinterpret_cast<LPARAM>(&all_displays));
+  return all_displays;
+}
+
+void ScreenWin::OnDisplayChanged() {
+  // Windows send a WM_DISPLAYCHANGE message to all windows when the displays
+  // change. This method will be called when this happen. In order to prevent
+  // doing expensive work multiple time, we use a timer that will be reset
+  // every time we get a new call and will be fulfilled kConfigureDelayMs after
+  // the latest.
+  if (configure_timer_.get() && configure_timer_->IsRunning()) {
+    configure_timer_->Reset();
+    return;
+  }
+
+  configure_timer_.reset(new base::OneShotTimer<ScreenWin>());
+  configure_timer_->Start(
+      FROM_HERE,
+      base::TimeDelta::FromMilliseconds(kConfigureDelayMs),
+      this,
+      &ScreenWin::ConfigureTimerFired);
+}
+
+void ScreenWin::ConfigureTimerFired() {
+  std::vector<gfx::Display> old_displays = displays_;
+  displays_ = BuildDisplays();
+
+  change_notifier_.NotifyDisplaysChanged(old_displays, displays_);
+}
+
 }  // namespace gfx