This function returns a drawable ID used to refer to the back buffer of the
specified window. The swap_action is a hint to indicate the swap action that
will likely be used in subsequent calls to
XdbeSwapBuffers().
The actual swap
action used in calls to
XdbeSwapBuffers()
does not have to be the same as the
swap_action passed to this function, though clients are encouraged to provide
accurate information whenever possible.
ERRORS
BadAlloc
BadIDChoice
BadMatch
The specified window is not an InputOutput window or its visual does not
support DBE.
