Allow upgrading to 2x DSF for lower UI scale when 2x resoruces are available.

ash/display/display_info.cc

 // Copyright (c) 2013 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 <stdio.h>
 #include <string>
 #include <vector>
 
 #include "ash/display/display_info.h"
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "ui/gfx/display.h"
 #include "ui/gfx/size_conversions.h"
 #include "ui/gfx/size_f.h"
 
 #if defined(OS_WIN)
 #include "ui/aura/window_tree_host.h"
 #include "ui/gfx/win/dpi.h"
 #endif
 
 namespace ash {
+namespace {
+
+bool allow_upgrade_to_high_dpi = false;
+
+}
 
 DisplayMode::DisplayMode()
     : refresh_rate(0.0f), interlaced(false), native(false) {}
 
 DisplayMode::DisplayMode(const gfx::Size& size,
                          float refresh_rate,
                          bool interlaced,
                          bool native)
     : size(size),
       refresh_rate(refresh_rate),
       interlaced(interlaced),
       native(native) {}
 
 // satic
 DisplayInfo DisplayInfo::CreateFromSpec(const std::string& spec) {
   return CreateFromSpecWithID(spec, gfx::Display::kInvalidDisplayID);
 }
 
 // static
+void DisplayInfo::SetAllowUpgradeToHighDPI(bool enable) {
+  allow_upgrade_to_high_dpi = enable;
+}
+
+// static
 DisplayInfo DisplayInfo::CreateFromSpecWithID(const std::string& spec,
                                               int64 id) {
   // Default bounds for a display.
   const int kDefaultHostWindowX = 200;
   const int kDefaultHostWindowY = 200;
   const int kDefaultHostWindowWidth = 1366;
   const int kDefaultHostWindowHeight = 768;
 
   // Use larger than max int to catch overflow early.
   static int64 synthesized_display_id = 2200000000LL;
@@ skipping 175 matching lines @@
   // is treated as a native so that it can be specified in
   // |CreateFromSpec|.
 }
 
 void DisplayInfo::SetBounds(const gfx::Rect& new_bounds_in_native) {
   bounds_in_native_ = new_bounds_in_native;
   size_in_pixel_ = new_bounds_in_native.size();
   UpdateDisplaySize();
 }
 
+float DisplayInfo::GetEffectiveDeviceScaleFactor() const {
+  if (allow_upgrade_to_high_dpi && configured_ui_scale_ < 1.0f &&
+      device_scale_factor_ == 1.0f) {
+    return 2.0f;
+  } else if (device_scale_factor_ == 2.0f && configured_ui_scale_ == 2.0f) {
+    return 1.0f;
+  }
+  return device_scale_factor_;
+}
+
 float DisplayInfo::GetEffectiveUIScale() const {
-  if (device_scale_factor_ == 2.0f && configured_ui_scale_ == 2.0f)
+  if (allow_upgrade_to_high_dpi && configured_ui_scale_ < 1.0f &&
+      device_scale_factor_ == 1.0f) {
+    return configured_ui_scale_ * 2.0f;
+  } else if (device_scale_factor_ == 2.0f && configured_ui_scale_ == 2.0f) {
     return 1.0f;
+  }
   return configured_ui_scale_;
 }
 
 void DisplayInfo::UpdateDisplaySize() {
   size_in_pixel_ = bounds_in_native_.size();
   if (!overscan_insets_in_dip_.empty()) {
     gfx::Insets insets_in_pixel =
         overscan_insets_in_dip_.Scale(device_scale_factor_);
     size_in_pixel_.Enlarge(-insets_in_pixel.width(), -insets_in_pixel.height());
   } else {
@@ skipping 58 matching lines @@
 }
 
 bool DisplayInfo::IsColorProfileAvailable(
     ui::ColorCalibrationProfile profile) const {
   return std::find(available_color_profiles_.begin(),
                    available_color_profiles_.end(),
                    profile) != available_color_profiles_.end();
 }
 
 }  // namespace ash