Compute the base dpi from X

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 1925e13cd9d18a880669eba77bdc66c6416b08fd..353a0149d9605422df733fd94585e9e4c224af3e 100644
--- a/chrome/browser/ui/libgtk2ui/gtk2_ui.cc
+++ b/chrome/browser/ui/libgtk2ui/gtk2_ui.cc
@@ -8,6 +8,7 @@
 #include <set>
 
 #include <pango/pango.h>
+#include <X11/Xlib.h>
 
 #include "base/command_line.h"
 #include "base/debug/leak_annotations.h"
@@ -49,6 +50,7 @@
 #include "ui/gfx/image/image.h"
 #include "ui/gfx/skbitmap_operations.h"
 #include "ui/gfx/skia_util.h"
+#include "ui/gfx/x/x11_types.h"
 #include "ui/resources/grit/ui_resources.h"
 #include "ui/views/controls/button/label_button.h"
 #include "ui/views/controls/button/label_button_border.h"
@@ -378,20 +380,27 @@ gfx::FontRenderParams GetGtkFontRenderParams() {
   return params;
 }
 
-double GetDPI() {
+double GetBaseDPI() {
+  XDisplay* xdisplay = gfx::GetXDisplay();
+  int xscreen = DefaultScreen(xdisplay);
+  return (DisplayHeight(xdisplay, xscreen) * 25.4) /
+         DisplayHeightMM(xdisplay, xscreen);
+}
+
+double GetFontDPI() {
   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.
-  return (gtk_dpi > 0) ? gtk_dpi / 1024.0 : 96.0;
+  return (gtk_dpi > 0) ? gtk_dpi / 1024.0 : GetBaseDPI();
 }
 
 // Queries GTK for its font DPI setting and returns the number of pixels in a
 // point.
 double GetPixelsInPoint(float device_scale_factor) {
-  double dpi = GetDPI();
+  double dpi = GetFontDPI();
 
   // Take device_scale_factor into account — if Chrome already scales the
   // entire UI up by 2x, we should not also scale up.
@@ -1424,10 +1433,9 @@ void Gtk2UI::UpdateDeviceScaleFactor(float device_scale_factor) {
 }
 
 float Gtk2UI::GetDeviceScaleFactor() const {
-  const int kCSSDefaultDPI = 96;
-  float scale = GetDPI() / kCSSDefaultDPI;
-  // Round to 2 decimals, e.g. to 1.33.
-  return roundf(scale * 100) / 100;
+  float scale = GetFontDPI() / GetBaseDPI();
+  // Round to 1 decimals, e.g. to 1.4.

[Evan Stade, 2015/05/14 22:43:04]

nit: 1 decimal

[oshima, 2015/05/14 22:45:12]

Done.

+  return roundf(scale * 10) / 10;
 }
 
 }  // namespace libgtk2ui