To provide a call-back function when a window is initially displayed.
Syntax
winio@('%sc', cb_func)
external cb_func
Description
Causes a given call-back to be called once only when a window is initially
displayed (for example, for drawing initial %gr - Graphics Region data).
Notes
If %gr (say) has a call-back function that receives the RESIZE message from
clearwin_info@('CALLBACK_REASON'), this message is received before the %sc
call-back is called.
Call-back functions can often be shared by different format codes within one
format window. For example, a call-back associated with %sc may also be
suitable for %mv - OnMove Callback.
