Unified Desktop: Support 2xDSF display

ash/display/display_manager.cc

Index: ash/display/display_manager.cc
diff --git a/ash/display/display_manager.cc b/ash/display/display_manager.cc
index 241f93c13adad4c334e6c7d07d82049453c26e43..a79a1f4c62188c8a2c198b268218a8368225951d 100644
--- a/ash/display/display_manager.cc
+++ b/ash/display/display_manager.cc
@@ -8,6 +8,7 @@
 #include <cmath>
 #include <set>
 #include <string>
+#include <utility>
 #include <vector>
 
 #include "ash/ash_switches.h"
@@ -1114,11 +1115,17 @@ void DisplayManager::CreateSoftwareMirroringDisplayInfo(
 
         // 1st Pass. Find the max size.
         int max_height = std::numeric_limits<int>::min();
-        for (auto& info : *display_info_list)
-          max_height = std::max(max_height, info.size_in_pixel().height());
+        float default_device_scale_factor = 1.0f;
+
+        for (auto& info : *display_info_list) {
+          if (max_height < info.size_in_pixel().height()) {
+            max_height = info.size_in_pixel().height();
+            default_device_scale_factor = info.device_scale_factor();

[Jun Mukai, 2015/07/29 21:26:28]

This means that if two displays are in the same height (i.e. in the same
resolution) but their DSF are different, the default one is the
device_scale_factor which happens to appear the first.
Considering HD Chromebook + external display or multiple 4K display
concatenations, I think it might be better to choose the lower-DSF as the
default.

[oshima, 2015/07/30 01:33:31]

Per offline discussion, changed to use the 1st or internal display as a default.

+          }
+        }
 
         std::vector<DisplayMode> display_mode_list;
-        std::set<float> scales;
+        std::set<std::pair<float, float>> dsf_scale_list;
 
         // 2nd Pass. Compute the unified display size.
         for (auto& info : *display_info_list) {
@@ -1131,14 +1138,17 @@ void DisplayManager::CreateSoftwareMirroringDisplayInfo(
               info.id(), origin, 1.0f / scale);
           unified_bounds.Union(display.bounds());
 
-          scales.insert(scale);
+          dsf_scale_list.insert(
+              std::make_pair(info.device_scale_factor(), scale));

[Jun Mukai, 2015/07/29 21:26:28]

Also, can we add a case of dsf=1.0 as an option?

[oshima, 2015/07/30 01:33:32]

Let's wait for user's feedback. My guess is that users want other resolutions
rather than 1.0dsf, but that should be easy to add.

         }
 
         DisplayInfo info(kUnifiedDisplayId, "Unified Desktop", false);
+        info.set_device_scale_factor(default_device_scale_factor);
         info.SetBounds(unified_bounds);
 
         DisplayMode native_mode(unified_bounds.size(), 60.0f, false, true);
-        info.SetDisplayModes(CreateUnifiedDisplayModeList(native_mode, scales));
+        info.SetDisplayModes(
+            CreateUnifiedDisplayModeList(native_mode, dsf_scale_list));
 
         // Forget the configured resolution if the original unified
         // desktop resolution has changed.
@@ -1153,7 +1163,7 @@ void DisplayManager::CreateSoftwareMirroringDisplayInfo(
         DisplayMode mode;
         if (GetSelectedModeForDisplayId(kUnifiedDisplayId, &mode) &&
             FindDisplayMode(info, mode) != info.display_modes().end()) {
-          // TODO(oshima): device scale factor.
+          info.set_device_scale_factor(mode.device_scale_factor);
           info.SetBounds(gfx::Rect(mode.size));
         } else {
           display_modes_.erase(kUnifiedDisplayId);