Use gtk to detect dpi.

sugar/activity/activity.py

@@ -32,11 +32,6 @@ class Activity(Window, gtk.Container):
     def __init__(self, handle):
         Window.__init__(self)
 
-        # FIXME: This will work only for activities in python. We need a xsetting.
-        display = gtk.gdk.display_manager_get().get_default_display()
-        screen = display.get_default_screen()
-        screen.set_resolution(_sugar.get_screen_dpi())
-
         self.connect('destroy', self._destroy_cb)
 
         self._shared = False

sugar/graphics/units.py

@@ -61,19 +61,18 @@ units to device units.
 
 import gtk
 
-import _sugar
-
 _MAX_ZOOM_FACTOR = 2.0
 _ZOOM_CONSTANT   = 650.0
 
 def _compute_zoom_factor():
     screen_width = gtk.gdk.screen_width()
-    if _sugar.get_screen_dpi() == 201.0 and screen_width == 1200:
+    if _screen_dpi == 201.0 and screen_width == 1200:
         return 1.0
     else:
         return min(_MAX_ZOOM_FACTOR, screen_width / _ZOOM_CONSTANT)
 
-_screen_dpi = float(_sugar.get_screen_dpi())
+_gtk_xft_dpi = gtk.settings_get_default().get_property('gtk-xft-dpi')
+_screen_dpi = float(_gtk_xft_dpi / 1024)
 _dpi_factor  = _screen_dpi / 201.0
 _zoom_factor = _compute_zoom_factor()