Enable subpixel positioning for internal display with dsf larger than 1.0

ui/gfx/font_render_params_linux.cc

Index: ui/gfx/font_render_params_linux.cc
diff --git a/ui/gfx/font_render_params_linux.cc b/ui/gfx/font_render_params_linux.cc
index f02636e8050c2da9466648995aada7952e1f09f6..77f8ba4b6521da1bca6d830fb167b3050844622d 100644
--- a/ui/gfx/font_render_params_linux.cc
+++ b/ui/gfx/font_render_params_linux.cc
@@ -23,6 +23,17 @@ namespace gfx {
 
 namespace {
 
+#if defined(OS_CHROMEOS)
+// A device scale factor for an internal display (if any)
+// that is used to determine if subpixel positioning should be used
+// instead of hinting.
+float device_scale_factor_for_internal_display = 1.0f;
+
+// Minimum device scale factor to enable text subpixel positioining
+// for internal display.
+const float kMinDsfToEnableSubpixelPositioning = 1.2f;

[Daniel Erat, 2014/08/19 22:32:25]

forget if i sent my previous comment asking this: why 1.2? can we just use it
for anything above 1.0? that's what blink does.

[oshima, 2014/08/20 01:41:12]

Done. I just removed const and use 1.0f as it's more obvious with 1.0f.

+#endif
+
 // Keyed by hashes of FontRenderParamQuery structs from
 // HashFontRenderParamsQuery().
 typedef base::MRUCache<uint32, FontRenderParams> Cache;
@@ -43,6 +54,15 @@ struct SynchronizedCache {
 base::LazyInstance<SynchronizedCache>::Leaky g_synchronized_cache =
     LAZY_INSTANCE_INITIALIZER;
 
+bool IsBrowserTextSubpixelPositioningEnabled() {
+#if defined(OS_CHROMEOS)
+  return device_scale_factor_for_internal_display >=
+         kMinDsfToEnableSubpixelPositioning;
+#else
+  return false;
+#endif
+}
+
 // Converts Fontconfig FC_HINT_STYLE to FontRenderParams::Hinting.
 FontRenderParams::Hinting ConvertFontconfigHintStyle(int hint_style) {
   switch (hint_style) {
@@ -187,10 +207,11 @@ FontRenderParams GetFontRenderParams(const FontRenderParamsQuery& query,
   } else {
     // Fontconfig doesn't support configuring subpixel positioning; check a
     // flag.
-    params.subpixel_positioning = CommandLine::ForCurrentProcess()->HasSwitch(
+    params.subpixel_positioning =
         query.for_web_contents ?
-        switches::kEnableWebkitTextSubpixelPositioning :
-        switches::kEnableBrowserTextSubpixelPositioning);
+        CommandLine::ForCurrentProcess()->HasSwitch(
+            switches::kEnableWebkitTextSubpixelPositioning) :
+        IsBrowserTextSubpixelPositioningEnabled();
 
     // To enable subpixel positioning, we need to disable hinting.
     if (params.subpixel_positioning)
@@ -217,4 +238,19 @@ void ClearFontRenderParamsCacheForTest() {
   synchronized_cache->cache.Clear();
 }
 
+#if defined(OS_CHROMEOS)
+void SetDeviceScaleFactorForInternalDisplay(float device_scale_factor) {
+  device_scale_factor_for_internal_display = device_scale_factor;
+}
+
+namespace test {
+
+bool GetBrowserTextSubpixelPoisitioningEnabled() {
+  return IsBrowserTextSubpixelPositioningEnabled();
+}
+
+}  // namespace test
+
+#endif
+
 }  // namespace gfx