Path: utzoo!attcan!utgpu!watmath!iuvax!rutgers!bellcore!dana
From: dana@dino.bellcore.com (Dana A. Chee)
Newsgroups: comp.windows.x
Subject: Re: Simple programming quiz
Message-ID: <DANA.89Jun15063723@dino.bellcore.com>
Date: 15 Jun 89 10:37:23 GMT
References: <29675@ucbvax.BERKELEY.EDU>
Sender: news@bellcore.bellcore.com
Organization: Bellcore, Morristown, NJ  USA
Lines: 78
In-reply-to: elf@gilan.Berkeley.EDU's message of 14 Jun 89 21:45:10 GMT

In article <29675@ucbvax.BERKELEY.EDU> elf@gilan.Berkeley.EDU (Marc Singer) writes:

   Why does this apparently simple X program not work?

   ----------------------

   /* test.c
   */
   #include <X11/Xlib.h>

   static char szLabel[] = "Hi there.";

   main()
   {
     Display *display;
     Window xwnd;
     XSetWindowAttributes attrib;
     XGCValues xgcv;
     GC gc;
     char ch;

     display = XOpenDisplay(0);

     attrib.background_pixel = WhilePixel(display, 0);
     attrib.border_pixel =     BlackPixel(display, 0);
     xwnd = XCreateWindow(display, RootWindow(display, 0),
			  10, 10, 500, 40,
			  2, CopyFromParent, InputOutput, CopyFromParent,
			  CWBackPixel | CWBorderPixel | CWEventMask, &attrib);

What's the event mask (attrib.event_mask = ?), since you set the flags
saying you were going to set it? (for problem below, you need at least
attrib.event_mask = Expose;)

     XMapWindow(display, xwnd);
     XFlush(display);

Great, now wait for an expose event that says your window has been
mapped.  Until that comes, you are drawing on the window before it is
being mapped and your strings and lines are going directly into the
bit bucket.  Add the following line (and define "Event event" above)

XNextEvent(display, &event);

   /*  xgcv.foreground = BlackPixel(display, 0); */
   /*  xgcv.function = GXinvert; */
   /*  xgcv.plane_mask = AllPlanes; */
   /*  gc = XCreateGC(display, xwnd, GCForeground | GCFunction | GCPlaneMask,
		    &xgcv); */
     gc = XCreateGC(display, xwnd, 0, 0);
     XDrawString(display, xwnd, gc, 10, 10, szLabel, strlen(szLabel));
     XDrawLine(display, xwnd, gc, 0, 0, 500, 40);
   /*  XFillRectangle(display, xwnd, gc, 0, 0, 1000, 1000); */
     XFlush(display);
     ch = getchar();
   }  /* main */

   ------------------  

   I know that some of the attributes for the window and the GC are
   redundant.  And I have tried specifying the visual and depth
   of the XCreateWindow explicitly.  Still, why do I not get anything
   other than a background in the window?

   Marc Singer
	   "When fullness is taken from fullness,
	    fullness still remains."
			   Invocation of the Isha Upanishad


The great "Drawing in an unmapped window" error strikes again.

--
			Dana Chee
			Bellcore
			MRE 2Q-250
			(201) 829-4488
			dana@bellcore.com