Feature: Automatic UI and font zoom levels when supported by the OS.

src/zoom_type.h

@@ -15,6 +15,8 @@
 static uint const ZOOM_LVL_SHIFT = 2;
 static uint const ZOOM_LVL_BASE  = 1 << ZOOM_LVL_SHIFT;
 
+static const int8 ZOOM_LVL_CFG_AUTO = -1;
+
 /** All zoom levels we know. */
 enum ZoomLevel : byte {
 	/* Our possible zoom-levels */
@@ -48,6 +50,9 @@ enum ZoomLevel : byte {
 };
 DECLARE_POSTFIX_INCREMENT(ZoomLevel)
 
+extern int8 _gui_zoom_cfg;
+extern int8 _font_zoom_cfg;
+
 extern ZoomLevel _gui_zoom;
 extern ZoomLevel _font_zoom;
 #define ZOOM_LVL_GUI (_gui_zoom)