device scale factor detection: use gtk-xft-dpi consistently

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 362 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;
 }
 
-// Queries GTK for its font DPI setting and returns the number of pixels in a
-// point.
-double GetPixelsInPoint(float device_scale_factor) {
+double GetDPI() {
   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;
+  return (gtk_dpi > 0) ? gtk_dpi / 1024.0 : 96.0;
+}
+
+// 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();
 
   // 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() {
@@ skipping 1010 matching lines @@
   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);
 }
 
+float Gtk2UI::GetDeviceScaleFactor() const {
+  const int kCSSDefaultDPI = 96;
+  const float scale = GetDPI() / kCSSDefaultDPI;
+  return ui::GetScaleForScaleFactor(ui::GetSupportedScaleFactor(scale));

[oshima, 2015/04/08 23:57:41]

you may want to add more scales for linux (133 150 etc).

[stapelberg, 2015/04/09 06:49:34]

Yeah, I’ll investigate that in a separate CL so that we can revert them
separately if necessary.

[oshima, 2015/04/09 17:22:23]

I think my comment was a bit confusing. Technically, you can just pass scale,
although we don't want to allow arbitrary scale factor. On Linux, we can pick
something like 1.25, 1.5 and 2.0 and use closest scale factor. (ChromeOS
currently support 1.0, 1.25 and 2.0)

+}
+
 }  // namespace libgtk2ui
 
 views::LinuxUI* BuildGtk2UI() {
   return new libgtk2ui::Gtk2UI;
 }