Modifies the threshold for hidpi displays.

ash/display/display_change_observer_chromeos.cc

 // Copyright 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 "ash/display/display_change_observer_chromeos.h"
 
 #include <algorithm>
 #include <map>
 #include <set>
 #include <vector>
@@ skipping 14 matching lines @@
 #include "ui/gfx/display.h"
 
 namespace ash {
 
 using ui::DisplayConfigurator;
 
 namespace {
 
 // The DPI threshold to detect high density screen.
 // Higher DPI than this will use device_scale_factor=2.
-const unsigned int kHighDensityDPIThreshold = 170;
+const unsigned int kHighDensityDPIThresholdSmall = 170;
+
+// The HiDPI threshold for large (usually external) monitors. Lower threshold
+// makes sense for large monitors, because such monitors should be located
+// farther from the user's face usually. See http://crbug.com/348279
+const unsigned int kHighDensityDPIThresholdLarge = 150;
+
+// The width threshold in mm for "large" monitors.
+const int kLargeDisplayWidthThresholdMM = 500;
 
 // 1 inch in mm.
 const float kInchInMm = 25.4f;
 
 // Display mode list is sorted by (in descending priority):
 //  * the area in pixels.
 //  * refresh rate.
 struct DisplayModeSorter {
   bool operator()(const DisplayMode& a, const DisplayMode& b) {
     if (a.size.GetArea() == b.size.GetArea())
@@ skipping 35 matching lines @@
   for (DisplayModeMap::const_iterator iter = display_mode_map.begin();
        iter != display_mode_map.end();
        ++iter) {
     display_mode_list.push_back(iter->second);
   }
   std::sort(
       display_mode_list.begin(), display_mode_list.end(), DisplayModeSorter());
   return display_mode_list;
 }
 
+// static
+float DisplayChangeObserver::GetScaleFactor(

[oshima, 2014/04/09 23:07:37]

can you move this (plus constants) to ui/display/display_util.h ?

[Jun Mukai, 2014/04/09 23:16:00]

Done.

+    const gfx::Size& physical_size,
+    const gfx::Size& screen_size) {
+  if (ui::IsDisplaySizeBlackListed(physical_size))
+    return 1.0f;
+
+  const unsigned int dpi = (kInchInMm * screen_size.width() /
+                            physical_size.width());
+  const unsigned int threshold =
+      (physical_size.width() >= kLargeDisplayWidthThresholdMM) ?
+      kHighDensityDPIThresholdLarge : kHighDensityDPIThresholdSmall;
+  return (dpi > threshold) ? 2.0f : 1.0f;
+}
+
 DisplayChangeObserver::DisplayChangeObserver() {
   Shell::GetInstance()->AddShellObserver(this);
 }
 
 DisplayChangeObserver::~DisplayChangeObserver() {
   Shell::GetInstance()->RemoveShellObserver(this);
 }
 
 ui::MultipleDisplayState DisplayChangeObserver::GetStateForDisplayIds(
     const std::vector<int64>& display_ids) const {
@@ skipping 25 matching lines @@
 
     if (state.display->type() == ui::DISPLAY_CONNECTION_TYPE_INTERNAL &&
         gfx::Display::InternalDisplayId() == gfx::Display::kInvalidDisplayID) {
       gfx::Display::SetInternalDisplayId(state.display->display_id());
     }
 
     const ui::DisplayMode* mode_info = state.display->current_mode();
     if (!mode_info)
       continue;
 
-    float device_scale_factor = 1.0f;
-    if (!ui::IsDisplaySizeBlackListed(state.display->physical_size()) &&
-        (kInchInMm * mode_info->size().width() /
-         state.display->physical_size().width()) > kHighDensityDPIThreshold) {
-      device_scale_factor = 2.0f;
-    }
+    float device_scale_factor = GetScaleFactor(
+        state.display->physical_size(), mode_info->size());
     gfx::Rect display_bounds(state.display->origin(), mode_info->size());
 
     std::vector<DisplayMode> display_modes = GetDisplayModeList(state);
 
     std::string name =
         state.display->type() == ui::DISPLAY_CONNECTION_TYPE_INTERNAL ?
             l10n_util::GetStringUTF8(IDS_ASH_INTERNAL_DISPLAY_NAME) :
             state.display->display_name();
     if (name.empty())
       name = l10n_util::GetStringUTF8(IDS_ASH_STATUS_TRAY_UNKNOWN_DISPLAY_NAME);
@@ skipping 23 matching lines @@
 
 void DisplayChangeObserver::OnAppTerminating() {
 #if defined(USE_ASH)
   // Stop handling display configuration events once the shutdown
   // process starts. crbug.com/177014.
   Shell::GetInstance()->display_configurator()->PrepareForExit();
 #endif
 }
 
 }  // namespace ash