Fix DPI scaling on Linux with GTK3

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;
 }
 
-double GetDpi() {
-  if (display::Display::HasForceDeviceScaleFactor())
-    return display::Display::GetForcedDeviceScaleFactor() * kDefaultDPI;
+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))
+    return -1;
 
+  return g_value_get_int(&scale);
+}
+
+float GetScaleFromDPI() {

[oshima, 2017/04/28 18:31:18]

nit: GetScaleFromXftDPI

[Chris Coulson, 2017/04/28 18:40:50]

Acknowledged.

   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 / 1024.0 : kDefaultDPI;
+  return (gtk_dpi > 0) ? gtk_dpi / (1024 * kDefaultDPI) : -1;
 }
 
 float GetRawDeviceScaleFactor() {
   if (display::Display::HasForceDeviceScaleFactor())
     return display::Display::GetForcedDeviceScaleFactor();
-  return GetDpi() / kDefaultDPI;
+
+  float scale = GetGdkWindowScalingFactor();
+  if (scale > 0)
+    return scale;
+
+  scale = GetScaleFromDPI();
+  if (scale > 0)
+    return scale;
+
+  return 1;
 }
 
 views::LinuxUI::NonClientMiddleClickAction GetDefaultMiddleClickAction() {
   std::unique_ptr<base::Environment> env(base::Environment::Create());
   switch (base::nix::GetDesktopEnvironment(env.get())) {
     case base::nix::DESKTOP_ENVIRONMENT_KDE4:
     case base::nix::DESKTOP_ENVIRONMENT_KDE5:
       // 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
@@ skipping 713 matching lines @@
 
 float GtkUi::GetDeviceScaleFactor() const {
   return device_scale_factor_;
 }
 
 }  // namespace libgtkui
 
 views::LinuxUI* BuildGtkUi() {
   return new libgtkui::GtkUi;
 }