allow for more control on refreshes when show()ing widgets

for now, we have show() automatically call setDirty() for the new
widget, as before. However, now show() takes two arguments for
refresh configuration that will get passed on to setDirty().

For compatibility, the default is here in show() to do a partial
refresh. So if you want no refresh triggered (via this show() call),
add a function that doesn't return anything.

frontend/ui/uimanager.lua

@@ -83,7 +83,8 @@ end
 
 -- register & show a widget
 -- modal widget should be always on the top
-function UIManager:show(widget, x, y)
+-- for refreshtype & refresharea see description of setDirty()
+function UIManager:show(widget, x, y, refreshtype, refresharea)
     DEBUG("show widget", widget.id)
     self._running = true
     local window = {x = x or 0, y = y or 0, widget = widget}
@@ -97,7 +98,7 @@ function UIManager:show(widget, x, y)
         end
     end
     -- and schedule it to be painted
-    self:setDirty(widget, "partial")
+    self:setDirty(widget, refreshtype or "partial", refresharea)
     -- tell the widget that it is shown now
     widget:handleEvent(Event:new("Show"))
     -- check if this widget disables double tap gesture
@@ -204,7 +205,7 @@ function UIManager:setDirty(widget, refreshtype, refreshregion)
         end
     end
     -- handle refresh information
-    if not refreshtype then return end
+    if not refreshtype or refreshtype == "none" then return end
     if type(refreshtype) == "function" then
         -- callback, will be issued after painting
         table.insert(self._refresh_func_stack, refreshtype)