Finds the descendant of this (including this itself) closest to the screen
at the point (
The point must be given in widget coordinates, so (0, 0) is assumed to be the top left of this's content area.
Usually widgets will return null if the given coordinate is not contained in this checked via contains. Otherwise they will recursively try to find a child that does not return null. Widgets are however free to customize their picking algorithm.
This function is used on the toplevel to determine the widget below the mouse cursor for purposes of hover highlighting and delivering events.
the widget to query
X coordinate to test, relative to this's origin
Y coordinate to test, relative to this's origin
Flags to influence what is picked
The widget descendant at the given coordinate or null if none.