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From: mouse@lightning.mcrcim.mcgill.EDU
Newsgroups: comp.windows.x
Subject: Re:  XDrawLine doesn't draw lines! Looking for help.
Message-ID: <9101250109.AA05849@lightning.McRCIM.McGill.EDU>
Date: 25 Jan 91 01:09:53 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 31

> I seem to be running into a problem when I use XDrawLine to draw a
> set of lines.  My program [...] reads from a text file 4 values at a
> time and draws a line using the read values as coordinates for the
> two endpoints.

> The program does not give any errors during compilation.  But I seem
> to get different results each time I execute the compiled code.
> Sometimes I get all lines drawn properly, sometimes none, sometimes a
> few.

>   theNewWindow = XCreateWindow( [...] );
>   XMapWindow(theDisplay, theNewWindow);
>   XFlush(theDisplay);
>   for (i=0; i<44; i++) {
>     fscanf(line_fin,"%d %d %d %d\n", &x1, &y1, &x2, &y2);
>     XDrawLine(theDisplay, theNewWindow, theGC, x1, y1, x2, y2);
>     }

See the FAQ, question #74.

Briefly: the window does not necessarily appear on the screen
immediately when you XMapWindow().  The window manager typically
redirects the request and does the map itself at a slightly later time.
All drawing done before the map actually happens will be lost.  You
should create the window with ExposureMask in the event-mask, then draw
whenever you get an Expose event.

					der Mouse

			old: mcgill-vision!mouse
			new: mouse@larry.mcrcim.mcgill.edu