Gtk: Consider font dpi when calculating device scale factor

chrome/browser/ui/libgtkui/gtk_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/libgtkui/gtk_ui.h"
 
 #include <X11/Xcursor/Xcursor.h>
 #include <dlfcn.h>
 #include <math.h>
 #include <pango/pango.h>
@@ skipping 297 matching lines @@
     LOG(WARNING) << "Unexpected gtk-xft-rgba \"" << rgba << "\"";
     params.subpixel_rendering = gfx::FontRenderParams::SUBPIXEL_RENDERING_NONE;
   }
 
   g_free(hint_style);
   g_free(rgba);
 
   return params;
 }
 
-float GetGdkWindowScalingFactor() {
-  GValue scale = G_VALUE_INIT;
-  g_value_init(&scale, G_TYPE_INT);
-  if (!gdk_screen_get_setting(gdk_screen_get_default(),
-                              "gdk-window-scaling-factor", &scale))
+float GtkDpiToScaleFactor(int dpi) {
+  // GTK multiplies the DPI by 1024 before storing it.
+  return dpi / (1024 * kDefaultDPI);
+}
+
+gint GetGdkScreenSettingInt(const char* setting_name) {
+  GValue value = G_VALUE_INIT;
+  g_value_init(&value, G_TYPE_INT);
+  if (!gdk_screen_get_setting(gdk_screen_get_default(), setting_name, &value))
     return -1;
+  return g_value_get_int(&value);
+}
 
-  return g_value_get_int(&scale);
+float GetScaleFromGdkScreenSettings() {
+  gint window_scale = GetGdkScreenSettingInt("gdk-window-scaling-factor");
+  if (window_scale <= 0)
+    return -1;
+  gint font_dpi = GetGdkScreenSettingInt("gdk-unscaled-dpi");
+  if (font_dpi <= 0)
+    return -1;
+  return window_scale * GtkDpiToScaleFactor(font_dpi);
 }
 
 float GetScaleFromXftDPI() {
   GtkSettings* gtk_settings = gtk_settings_get_default();
   CHECK(gtk_settings);
   gint gtk_dpi = -1;
   g_object_get(gtk_settings, "gtk-xft-dpi", &gtk_dpi, nullptr);
-  // GTK multiplies the DPI by 1024 before storing it.
-  return (gtk_dpi > 0) ? gtk_dpi / (1024 * kDefaultDPI) : -1;
+  if (gtk_dpi <= 0)
+    return -1;
+  return GtkDpiToScaleFactor(gtk_dpi);
 }
 
 float GetRawDeviceScaleFactor() {
   if (display::Display::HasForceDeviceScaleFactor())
     return display::Display::GetForcedDeviceScaleFactor();
 
-  float scale = GetGdkWindowScalingFactor();
+  float scale = GetScaleFromGdkScreenSettings();
   if (scale > 0)
     return scale;
 
   scale = GetScaleFromXftDPI();
   if (scale > 0)
     return scale;
 
   return 1;
 }
 
@@ skipping 721 matching lines @@
 
 float GtkUi::GetDeviceScaleFactor() const {
   return device_scale_factor_;
 }
 
 }  // namespace libgtkui
 
 views::LinuxUI* BuildGtkUi() {
   return new libgtkui::GtkUi;
 }