Fix Pango font rendering with HiDPi displays on Linux.

chrome/browser/ui/libgtk2ui/gtk2_ui.cc

Index: chrome/browser/ui/libgtk2ui/gtk2_ui.cc
diff --git a/chrome/browser/ui/libgtk2ui/gtk2_ui.cc b/chrome/browser/ui/libgtk2ui/gtk2_ui.cc
index 5405a718ef1f540515ff20cf0e15580cd44a3d20..be03b6d7013f3ae432ed4cd677f37801566b41d7 100644
--- a/chrome/browser/ui/libgtk2ui/gtk2_ui.cc
+++ b/chrome/browser/ui/libgtk2ui/gtk2_ui.cc
@@ -381,7 +381,7 @@ gfx::FontRenderParams GetGtkFontRenderParams() {
 
 // Queries GTK for its font DPI setting and returns the number of pixels in a
 // point.
-double GetPixelsInPoint() {
+double GetPixelsInPoint(float device_scale_factor) {
   GtkSettings* gtk_settings = gtk_settings_get_default();
   CHECK(gtk_settings);
   gint gtk_dpi = -1;
@@ -390,6 +390,10 @@ double GetPixelsInPoint() {
   // GTK multiplies the DPI by 1024 before storing it.
   double dpi = (gtk_dpi > 0) ? gtk_dpi / 1024.0 : 96.0;
 
+  // Take device_scale_factor into account — if Chrome already scales the
+  // entire UI up by 2x, we should not also scale up.
+  dpi /= device_scale_factor;
+
   // There are 72 points in an inch.
   return dpi / 72.0;
 }
@@ -413,7 +417,8 @@ views::LinuxUI::NonClientMiddleClickAction GetDefaultMiddleClickAction() {
 Gtk2UI::Gtk2UI()
     : default_font_size_pixels_(0),
       default_font_style_(gfx::Font::NORMAL),
-      middle_click_action_(GetDefaultMiddleClickAction()) {
+      middle_click_action_(GetDefaultMiddleClickAction()),
+      device_scale_factor_(1.0) {
   GtkInitFromCommandLine(*base::CommandLine::ForCurrentProcess());
 }
 
@@ -692,7 +697,7 @@ void Gtk2UI::GetDefaultFontDescription(
     std::string* family_out,
     int* size_pixels_out,
     int* style_out,
-    gfx::FontRenderParams* params_out) const {
+    gfx::FontRenderParams* params_out) {

[Daniel Erat, 2015/03/16 13:57:53]

can't this still be const? it doesn't look like you made any changes to it.

[stapelberg, 2015/03/17 08:36:33]

You’re right. I forgot to change this back after refactoring. Done.

   *family_out = default_font_family_;
   *size_pixels_out = default_font_size_pixels_;
   *style_out = default_font_style_;
@@ -1384,7 +1389,7 @@ void Gtk2UI::UpdateDefaultFont(const PangoFontDescription* desc) {
     const double size_points = pango_font_description_get_size(desc) /
         static_cast<double>(PANGO_SCALE);
     default_font_size_pixels_ = static_cast<int>(
-        GetPixelsInPoint() * size_points + 0.5);
+        GetPixelsInPoint(device_scale_factor_) * size_points + 0.5);
     query.point_size = static_cast<int>(size_points);
   }
 
@@ -1407,6 +1412,12 @@ void Gtk2UI::OnStyleSet(GtkWidget* widget, GtkStyle* previous_style) {
   NativeThemeGtk2::instance()->NotifyObservers();
 }
 
+void Gtk2UI::UpdateDeviceScaleFactor(float device_scale_factor) {
+  device_scale_factor_ = device_scale_factor;
+  GtkStyle* label_style = gtk_rc_get_style(fake_label_.get());
+  UpdateDefaultFont(label_style->font_desc);
+}
+
 }  // namespace libgtk2ui
 
 views::LinuxUI* BuildGtk2UI() {