Use 1.25 DSF for 150~180 DPI

BUG=372212

Review URL: https://codereview.chromium.org/411763004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285115 0039d316-1c4b-4281-b951-d872f2087c98

ash/display/display_change_observer_chromeos.cc

@@ -30,9 +30,18 @@ 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;
+// The DPI threshold to determine the device scale factor.
+// DPI higher than |dpi| will use |device_scale_factor|.
+struct DeviceScaleFactorDPIThreshold {
+  float dpi;
+  float device_scale_factor;
+};
+
+const DeviceScaleFactorDPIThreshold kThresholdTable[] = {
+  {180.0f, 2.0f},
+  {150.0f, 1.25f},
+  {0.0f, 1.0f},
+};
 
 // 1 inch in mm.
 const float kInchInMm = 25.4f;
@@ -134,10 +143,10 @@ void DisplayChangeObserver::OnDisplayModeChanged(
       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;
+    if (!ui::IsDisplaySizeBlackListed(state.display->physical_size())) {
+      device_scale_factor =
+          FindDeviceScaleFactor((kInchInMm * mode_info->size().width() /
+                                 state.display->physical_size().width()));
     }
     gfx::Rect display_bounds(state.display->origin(), mode_info->size());
 
@@ -184,4 +193,13 @@ void DisplayChangeObserver::OnAppTerminating() {
 #endif
 }
 
+// static
+float DisplayChangeObserver::FindDeviceScaleFactor(float dpi) {
+  for (size_t i = 0; i < arraysize(kThresholdTable); ++i) {
+    if (dpi > kThresholdTable[i].dpi)
+      return kThresholdTable[i].device_scale_factor;
+  }
+  return 1.0f;
+}
+
 }  // namespace ash

ash/display/display_change_observer_chromeos.h

@@ -40,6 +40,9 @@ class DisplayChangeObserver : public ui::DisplayConfigurator::StateController,
   // Overriden from ShellObserver:
   virtual void OnAppTerminating() OVERRIDE;
 
+  // Exposed for testing.
+  ASH_EXPORT static float FindDeviceScaleFactor(float dpi);
+
  private:
   DISALLOW_COPY_AND_ASSIGN(DisplayChangeObserver);
 };

ash/display/display_change_observer_chromeos_unittest.cc

@@ -82,4 +82,29 @@ TEST_F(DisplayChangeObserverTest, GetDisplayModeList) {
   EXPECT_EQ(0u, display_modes.size());
 }
 
+TEST_F(DisplayChangeObserverTest, FindDeviceScaleFactor) {
+  // 19.5" 1600x900
+  EXPECT_EQ(1.0f, DisplayChangeObserver::FindDeviceScaleFactor(94.14f));
+
+  // 21.5" 1920x1080
+  EXPECT_EQ(1.0f, DisplayChangeObserver::FindDeviceScaleFactor(102.46f));
+
+  // 12.1" 1280x800
+  EXPECT_EQ(1.0f, DisplayChangeObserver::FindDeviceScaleFactor(124.75f));
+
+  // 13.3" 1920x1080
+  EXPECT_EQ(1.25f, DisplayChangeObserver::FindDeviceScaleFactor(157.35f));
+
+  // 14" 1920x1080
+  EXPECT_EQ(1.25f, DisplayChangeObserver::FindDeviceScaleFactor(165.63f));
+
+  // 12.85" 2560x1700
+  EXPECT_EQ(2.0f, DisplayChangeObserver::FindDeviceScaleFactor(239.15f));
+
+  // Erroneous values should still work.
+  EXPECT_EQ(1.0f, DisplayChangeObserver::FindDeviceScaleFactor(-100.0f));
+  EXPECT_EQ(1.0f, DisplayChangeObserver::FindDeviceScaleFactor(0.0f));
+  EXPECT_EQ(2.0f, DisplayChangeObserver::FindDeviceScaleFactor(10000.0f));
+}
+
 }  // namespace ash