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From: bruce@servio.UUCP (Bruce Schuchardt)
Newsgroups: comp.windows.x
Subject: Re: XDrawLine
Message-ID: <278@servio.UUCP>
Date: 5 Dec 89 22:23:43 GMT
References: <1989Dec2.193728.2991@athena.mit.edu>
Reply-To: bruce@servio.UUCP (Bruce Schuchardt)
Distribution: usa
Organization: Servio Logic Development Corp.; Beaverton, OR
Lines: 50

In article <1989Dec2.193728.2991@athena.mit.edu> jstravis@athena.mit.edu (John S. Travis) writes:
>Can anyone help me with what must be an obvious(to others) error
>I am merely trying to read in some data ponts and draw lines
>connecting them. The window pops up, but nothing is drawn, not even
>the XDrawLines i threw in randomly throughout the program. What's the deal?
>Thanks for any help!
>
  [ deleted ]
>
>  toplevel = XtInitialize(argv[0],"Stream",NULL,0,&argc,argv);
>  canvas = XtCreateManagedWidget("canvas",XwworkSpaceWidgetClass,toplevel,NULL,0);
>  XtRealizeWidget(toplevel);
>
  [ deleted ]
>  gc = XtGetGC(canvas,GCForeground | GCLineWidth | GCBackground, &values);
>
>  XDrawLine(XtDisplay(canvas), XtWindow(canvas),gc, 24,89,30,133);
>
  [ deleted ]
>  XtMainLoop();
>}
  [ deleted ]

I'm surprised you didn't get an Invalid Window error from the server with
this code.  Calling XtRealizeWidget() doesn't complete the job of getting
a window up on the screen.  This won't happen until some events are dispatched
(e.g., in XtMainLoop()).  You can draw all you want, but it won't go on the
widget's window if the widget doesn't have a mapped window yet.

I had a similar problem, where I wanted to create and map a widget and then
do some other good stuff all in the same function.  Here's what I did:

  /* try to get a real widget window */
  while (!XtIsRealized(widget)  &&  XtPending()) {
    XtNextEvent(&event);
    XtDispatchEvent(&event);
  }

  if (XtIsRealized(widget)) {
    /* do your drawing here */
  }
  else {
    /* something went haywire */
  }

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Bruce Schuchardt          Ph: (503) 629-8383
  Servio Logic              bruce@servio.SLC.COM
  Beaverton, OR             uunet!servio!bruce