Starts moving a window.
This function is used if an application has window movement grips. When GDK can support it, the window movement will be done using the standard mechanism for the window manager or windowing system. Otherwise, GDK will try to emulate window movement, potentially not all that well, depending on the windowing system.
mouse button that initiated the drag
X position where the user clicked to initiate the drag, in root window coordinates
Y position where the user clicked to initiate the drag
timestamp from the click event that initiated the drag