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

ui/base/win/dpi.cc

Index: ui/base/win/dpi.cc
diff --git a/ui/base/win/dpi.cc b/ui/base/win/dpi.cc
index 9c56af05b9febd994de39b88bd2a7b589fdb824b..ecfb3e7a31e477ff93b3e4a19394bd2d6ced2d09 100644
--- a/ui/base/win/dpi.cc
+++ b/ui/base/win/dpi.cc
@@ -7,12 +7,26 @@
 #include <windows.h>
 
 #include "base/win/scoped_hdc.h"
+#include "ui/gfx/display.h"
+#include "ui/gfx/point_conversions.h"
+#include "ui/gfx/rect_conversions.h"
+#include "ui/gfx/size_conversions.h"
 
 namespace {
 
 int kDefaultDPIX = 96;
 int kDefaultDPIY = 96;
 
+
+float GetDeviceScaleFactorImpl() {
+#if defined(ENABLE_HIDPI)
+  return gfx::Display::HasForceDeviceScaleFactor() ?
+      gfx::Display::GetForcedDeviceScaleFactor() : ui::GetDPIScale();
+#else
+  return 1.0f;
+#endif
+}
+
 }  // namespace
 
 namespace ui {
@@ -53,4 +67,39 @@ void EnableHighDPISupport() {
     set_process_dpi_aware_func();
 }
 
+namespace win {
+
+float GetDeviceScaleFactor() {

[darin (slow to review), 2013/01/30 21:39:12]

What happens in the case of multiple monitors, each having different device
scale factors?

[kevers, 2013/01/30 22:27:01]

Under Windows, all monitors use the same scale factor.  The DPI value (used to
compute the scale factor) is set to a constant value in the OS and will remain
constant for the life of the application (requires logging out for a change to
take effect).
 

+  static const float device_scale_factor = GetDeviceScaleFactorImpl();
+  return device_scale_factor;
+}
+
+gfx::Point ScreenToDIPPoint(const gfx::Point& pixel_point) {
+  return gfx::ToFlooredPoint(
+      gfx::ScalePoint(pixel_point, 1.0f / GetDeviceScaleFactor()));
+}
+
+gfx::Rect ScreenToDIPRect(const gfx::Rect& pixel_bounds) {
+  // TODO(kevers): Switch to non-deprecated method for float to int conversions.
+  return gfx::ToFlooredRectDeprecated(
+      gfx::ScaleRect(pixel_bounds, 1.0f / GetDeviceScaleFactor()));
+}
+
+gfx::Rect DIPToScreenRect(const gfx::Rect& dip_bounds) {
+  // TODO(kevers): Switch to non-deprecated method for float to int conversions.
+  return gfx::ToFlooredRectDeprecated(
+      gfx::ScaleRect(dip_bounds, GetDeviceScaleFactor()));
+}
+
+gfx::Size ScreenToDIPSize(const gfx::Size& size_in_pixels) {
+  return gfx::ToFlooredSize(
+      gfx::ScaleSize(size_in_pixels, 1.0f / GetDeviceScaleFactor()));
+}
+
+gfx::Size DIPToScreenSize(const gfx::Size& dip_size) {
+  return gfx::ToFlooredSize(gfx::ScaleSize(dip_size, GetDeviceScaleFactor()));
+}
+
+}  // namespace win
+
 }  // namespace ui