Added option to center the mouse instead of restoring position. Useful

option for users and improves functionality after adding/removing
monitors with xrandr.

lib/awful/screen.lua

@@ -93,15 +93,21 @@ end
 -- @tparam screen _screen Screen number (defaults / falls back to mouse.screen).
 -- @request client activate screen.focus granted The most recent focused client
 --  for this screen should be re-activated.
-function screen.focus(_screen)
+function screen.focus(_screen, ...)
     client = client or require("awful.client")
     if type(_screen) == "number" and _screen > capi.screen.count() then _screen = screen.focused() end
     _screen = get_screen(_screen)
+    if select('#', ...) == 0 then center_mouse = false else center_mouse = select(1, ...) or false end
 
     -- screen and pos for current screen
     local s = get_screen(capi.mouse.screen)
     local pos
-
+    -- center the mouse if requested, else restore previous position
+    if center_mouse then
+        pos = capi.mouse.coords()
+        pos.x = _screen.geometry.x +  _screen.geometry.width/2
+        pos.y = _screen.geometry.y +  _screen.geometry.height/2
+    else
         if not _screen.mouse_per_screen then
             -- This is the first time we enter this screen,
             -- keep relative mouse position on the new screen.
@@ -115,6 +121,7 @@ function screen.focus(_screen)
             -- restore mouse position
             pos = _screen.mouse_per_screen
         end
+    end
 
     -- save pointer position of current screen
     s.mouse_per_screen = capi.mouse.coords()