Refactor Windows DPI Point, Rect, and Size for Multiple Monitor DPI Awareness

ui/gfx/win/dpi.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/win/dpi.h"
 
 #include <windows.h>
 #include "base/win/scoped_hdc.h"
 #include "ui/gfx/display.h"
 #include "ui/gfx/geometry/point_conversions.h"
 #include "ui/gfx/geometry/rect_conversions.h"
 #include "ui/gfx/geometry/size_conversions.h"
+#include "ui/gfx/screen.h"
 
 namespace {
 
 const float kDefaultDPI = 96.f;
 
 float g_device_scale_factor = 0.f;
 
 float GetUnforcedDeviceScaleFactor() {
-  return g_device_scale_factor ?
-      g_device_scale_factor :
-      static_cast<float>(gfx::GetDPI().width()) / kDefaultDPI;
+  if (g_device_scale_factor)
+    return g_device_scale_factor;
+
+  static float device_scale_factor = 0.0f;
+  if (!device_scale_factor) {
+    base::win::ScopedGetDC screen_dc(NULL);
+    int dpi_x = GetDeviceCaps(screen_dc, LOGPIXELSX);
+    DCHECK(dpi_x == GetDeviceCaps(screen_dc, LOGPIXELSY));
+    device_scale_factor = static_cast<float>(dpi_x) / kDefaultDPI;
+  }
+  return device_scale_factor;
 }
 
 }  // namespace
 
 namespace gfx {
 
 void SetDefaultDeviceScaleFactor(float scale) {
   DCHECK_NE(0.f, scale);
   g_device_scale_factor = scale;
 }
 
-Size GetDPI() {
-  static int dpi_x = 0;
-  static int dpi_y = 0;
-  static bool should_initialize = true;
-
-  if (should_initialize) {
-    should_initialize = false;
-    base::win::ScopedGetDC screen_dc(NULL);
-    // This value is safe to cache for the life time of the app since the
-    // user must logout to change the DPI setting. This value also applies
-    // to all screens.
-    dpi_x = GetDeviceCaps(screen_dc, LOGPIXELSX);
-    dpi_y = GetDeviceCaps(screen_dc, LOGPIXELSY);
-  }
-  return Size(dpi_x, dpi_y);
+int GetDPIFromScalingFactor(float device_scaling_factor) {
+  return kDefaultDPI * device_scaling_factor;
 }
 
 float GetDPIScale() {
   if (gfx::Display::HasForceDeviceScaleFactor())
     return gfx::Display::GetForcedDeviceScaleFactor();
   float dpi_scale = GetUnforcedDeviceScaleFactor();
   return (dpi_scale <= 1.25f) ? 1.f : dpi_scale;
 }
 
 namespace win {
 
-Point ScreenToDIPPoint(const Point& pixel_point) {
-  return ScaleToFlooredPoint(pixel_point, 1.0f / GetDPIScale());
-}
-
-Point DIPToScreenPoint(const Point& dip_point) {
-  return ScaleToFlooredPoint(dip_point, GetDPIScale());
-}
-
-Rect ScreenToDIPRect(const Rect& pixel_bounds) {
-  // It's important we scale the origin and size separately. If we instead
-  // calculated the size from the floored origin and ceiled right the size could
-  // vary depending upon where the two points land. That would cause problems
-  // for the places this code is used (in particular mapping from native window
-  // bounds to DIPs).
-  return Rect(ScreenToDIPPoint(pixel_bounds.origin()),
-              ScreenToDIPSize(pixel_bounds.size()));
-}
-
-Rect DIPToScreenRect(const Rect& dip_bounds) {
-  // See comment in ScreenToDIPRect for why we calculate size like this.
-  return Rect(DIPToScreenPoint(dip_bounds.origin()),
-              DIPToScreenSize(dip_bounds.size()));
-}
-
-Size ScreenToDIPSize(const Size& size_in_pixels) {
-  // Always ceil sizes. Otherwise we may be leaving off part of the bounds.
-  return ScaleToCeiledSize(size_in_pixels, 1.0f / GetDPIScale());
-}
-
-Size DIPToScreenSize(const Size& dip_size) {
-  // Always ceil sizes. Otherwise we may be leaving off part of the bounds.
-  return ScaleToCeiledSize(dip_size, GetDPIScale());
-}
-
 int GetSystemMetricsInDIP(int metric) {
   // The system metrics always reflect the system DPI, not whatever scale we've
   // forced or decided to use.
   return static_cast<int>(
       std::round(GetSystemMetrics(metric) / GetUnforcedDeviceScaleFactor()));
 }
 
 }  // namespace win
 }  // namespace gfx