Automatic DPI for all platforms, per monitor DPI for Windows.

For Windows 8.1 and X11 (Linux, BSD) now use the DPI specified by the operating
system, which previously only worked on macOS. For Windows this is handled per
monitor, for X11 this is based on Xft.dpi or xrandr --dpi. This should result
in appropriate font and button sizes by default in most cases.

The UI has been simplified to a single UI Scale factor relative to the automatic
DPI, instead of two DPI and Virtual Pixel Size settings. There is forward and
backwards compatibility for existing user preferences.

Reviewed By: brecht, LazyDodo

Differential Revision: https://developer.blender.org/D2539

release/scripts/startup/bl_ui/space_userpref.py

@@ -217,6 +217,7 @@ class USERPREF_PT_interface(Panel):
 
         col = row.column()
         col.label(text="Display:")
+        col.prop(view, "ui_scale", text="Scale")
         col.prop(view, "show_tooltips")
         col.prop(view, "show_tooltips_python")
         col.prop(view, "show_object_info", text="Object Info")
@@ -467,11 +468,6 @@ class USERPREF_PT_system(Panel):
 
         col = colsplit.column()
         col.label(text="General:")
-        col.prop(system, "dpi")
-        col.label("Virtual Pixel Mode:")
-        col.prop(system, "virtual_pixel_mode", text="")
-
-        col.separator()
 
         col.prop(system, "frame_server_port")
         col.prop(system, "scrollback", text="Console Scrollback")