Fix high-DPI on Windows to make use of DIP scaling in WebKit.

ui/surface/accelerated_surface_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/surface/accelerated_surface_win.h"
 
 #include <windows.h>
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/file_path.h"
 #include "base/lazy_instance.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop_proxy.h"
 #include "base/scoped_native_library.h"
 #include "base/stringprintf.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/time.h"
 #include "base/win/wrapped_window_proc.h"
+#include "ui/base/win/dpi.h"
 #include "ui/base/win/hwnd_util.h"
 #include "ui/gfx/rect.h"
 #include "ui/gl/gl_switches.h"
 #include "ui/surface/accelerated_surface_transformer_win.h"
 #include "ui/surface/d3d9_utils_win.h"
 #include "ui/surface/surface_switches.h"
 
 namespace d3d_utils = ui_surface_d3d9_utils;
 
 namespace {
@@ skipping 446 matching lines @@
   // If invalidated, do nothing, the window is gone.
   if (!window_) {
     TRACE_EVENT0("gpu", "EarlyOut_NoWindow");
     return;
   }
 
 #if !defined(USE_AURA)
   // If the window is a different size than the swap chain that is being
   // presented then drop the frame.
   gfx::Size window_size = GetWindowSize();
-  if (hidden_ && size != window_size) {
+#if defined(ENABLE_HIDPI)
+  // Check if the size mismatch is within allowable round off or truncation
+  // error.
+  gfx::Size dip_size = ui::win::ScreenToDIPSize(window_size);
+  gfx::Size pixel_size = ui::win::DIPToScreenSize(dip_size);
+  bool size_mismatch = abs(window_size.width() - size.width()) >
+      abs(window_size.width() - pixel_size.width()) ||
+      abs(window_size.height() - size.height()) >
+      abs(window_size.height() - pixel_size.height());
+#else
+  bool size_mismatch = size != window_size;
+#endif
+  if (hidden_ && size_mismatch) {
     TRACE_EVENT2("gpu", "EarlyOut_WrongWindowSize",
                  "backwidth", size.width(), "backheight", size.height());
     TRACE_EVENT2("gpu", "EarlyOut_WrongWindowSize2",
                  "windowwidth", window_size.width(),
                  "windowheight", window_size.height());
     return;
   }
 #endif
 
   // Round up size so the swap chain is not continuously resized with the
@@ skipping 289 matching lines @@
   presenter_->AsyncCopyTo(src_subrect, dst_size, buf, callback);
 }
 
 void AcceleratedSurface::Suspend() {
   presenter_->Suspend();
 }
 
 void AcceleratedSurface::WasHidden() {
   presenter_->WasHidden();
 }