Path: utzoo!attcan!uunet!husc6!bloom-beacon!ATHENA.MIT.EDU!kit
From: kit@ATHENA.MIT.EDU (Chris D. Peterson)
Newsgroups: comp.windows.x
Subject: Re: How do I draw on a widget?
Message-ID: <8812162153.AA16365@DORA.MIT.EDU>
Date: 16 Dec 88 21:53:43 GMT
References: <10461@umn-cs.CS.UMN.EDU>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 61

In reply to: randy@umn-cs.arpa (Randy Orrison) message of 16 December.

The most likely cause of your problem is that you are trying to draw in a 
widget that does not have a window associated with it.  Only widgets that
have been realized have real X windows associated with them.  A call to
XtIsRealized() may be appropriate.

When I just want a plain window to draw into I usually just instanciate
a core widget, class is widgetClass.  In order for this to work you must
understand X events.

References:		Xlib Manual Chapter 8 and Xt Manual Chapter 7.

Example:

NOTE: 	Rattled off here, has NOT been tested, but I hope you will get the
	general idea.


main(argc, argv)
int argc;
char ** argv;
{
	Widget foo, bar;
	Arg arglist[10];
	Cardinal num_args;
	static void DrawProc();

	bar = XtInitialize( NULL, "foo_bar", NULL, 0, &argc, argv);
	num_args = 0;
	XtSetArg(arglist[num_args], XtNwidth, 100); num_args++;
	XtSetArg(arglist[num_args], XtNheight, 100); num_args++;
	foo = XtCreateManagedWidget( "window", bar, widgetClass, arglist,
				    num_args);
	XtAddEventHandler(foo, ExposureMask, FALSE, DrawProc, NULL);
	XtRealizeWidget(bar);
	XtMainLoop();
}

static void
DrawProc(w, junk, event)
Widget w;
caddr_t junk;
XEvent *event;
{

/* Insert drawing code here, make sure to check the count in the
 * exposure structure, or you may draw the graphics multiple times 
 * on every exposure.
 */
}

						Chris D. Peterson     
						MIT X Consortium /
						Project Athena 

Net:	kit@athena.mit.edu		
Phone: (617) 253 - 1326			
USMail: MIT - Room E40-342C		
	77 Massachusetts Ave.		
	Cambridge, MA 02139