Fix Pango font rendering with HiDPi displays on Linux.

chrome/browser/ui/libgtk2ui/gtk2_ui.cc

 // Copyright (c) 2012 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 "chrome/browser/ui/libgtk2ui/gtk2_ui.h"
 
 #include <set>
 
 #include <pango/pango.h>
 
@@ skipping 363 matching lines @@
   }
 
   g_free(hint_style);
   g_free(rgba);
 
   return params;
 }
 
 // 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;
   g_object_get(gtk_settings, "gtk-xft-dpi", &gtk_dpi, NULL);
 
   // 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;
 }
 
 views::LinuxUI::NonClientMiddleClickAction GetDefaultMiddleClickAction() {
   scoped_ptr<base::Environment> env(base::Environment::Create());
   switch (base::nix::GetDesktopEnvironment(env.get())) {
     case base::nix::DESKTOP_ENVIRONMENT_KDE4:
       // Starting with KDE 4.4, windows' titlebars can be dragged with the
       // middle mouse button to create tab groups. We don't support that in
       // Chrome, but at least avoid lowering windows in response to middle
       // clicks to avoid surprising users who expect the KDE behavior.
       return views::LinuxUI::MIDDLE_CLICK_ACTION_NONE;
     default:
       return views::LinuxUI::MIDDLE_CLICK_ACTION_LOWER;
   }
 }
 
 }  // namespace
 
 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());
 }
 
 void Gtk2UI::Initialize() {
   signals_.reset(new Gtk2SignalRegistrar);
 
   // Create our fake widgets.
   fake_window_ = gtk_window_new(GTK_WINDOW_TOPLEVEL);
   fake_frame_ = chrome_gtk_frame_new();
   fake_label_.Own(gtk_label_new(""));
@@ skipping 950 matching lines @@
     // PANGO_SCALE Pango units in a device unit (pixel).
     const int size_pixels = pango_font_description_get_size(desc) / PANGO_SCALE;
     default_font_size_pixels_ = size_pixels;
     query.pixel_size = size_pixels;
   } else {
     // Non-absolute sizes are in points (again scaled by PANGO_SIZE).
     // Round the value when converting to pixels to match GTK's logic.
     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);
   }
 
   query.style = gfx::Font::NORMAL;
   // TODO(davemoore): Support weights other than bold?
   if (pango_font_description_get_weight(desc) == PANGO_WEIGHT_BOLD)
     query.style |= gfx::Font::BOLD;
   // TODO(davemoore): What about PANGO_STYLE_OBLIQUE?
   if (pango_font_description_get_style(desc) == PANGO_STYLE_ITALIC)
     query.style |= gfx::Font::ITALIC;
 
   default_font_render_params_ =
       gfx::GetFontRenderParams(query, &default_font_family_);
   default_font_style_ = query.style;
 }
 
 void Gtk2UI::OnStyleSet(GtkWidget* widget, GtkStyle* previous_style) {
   ClearAllThemeData();
   LoadGtkValues();
   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() {
   return new libgtk2ui::Gtk2UI;
 }