Path: utzoo!attcan!uunet!lll-winken!ames!ncar!husc6!bloom-beacon!ATHENA.MIT.EDU!kit
From: kit@ATHENA.MIT.EDU (Chris D. Peterson)
Newsgroups: comp.windows.x
Subject: Re: Xlib and Widgets, again
Message-ID: <8901262013.AA03017@DORA.MIT.EDU>
Date: 26 Jan 89 20:13:55 GMT
References: <9012@burdvax.PRC.Unisys.COM>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 60


> From: coltoff@burdvax.prc.unisys.com (Joel Coltoff)

> In article <16672@iuvax.cs.indiana.edu> beckman@iuvax.cs.indiana.edu (Peter 
> Beckman) writes:
> >dpy = XtDisplay(Widget);
> >myXGCV.foreground = WhitePixel(dpy, DefaultScreen(dpy));
> >myXGCV.background = BlackPixel(dpy, DefaultScreen(dpy));
> >valuemask = GCForeground | GCBackground;
> >gc = XtGetGC(Widget, valuemask, &myXGCV);
> >win = XtWindow(Widget);
> >
> >XFillRectangle(dpy,win,gc,0,0,400,400);

> Having just been down that road I'll take a shot at this. First of all
> you are changing entries in the values structure when you call XtGetGC().
> This is a definite NO NO. Here is the code that works for me in my text
> widget. The copyMask is set to all values that XFillRectangle() uses
> minus those I'm going to change anyway.

[code deleted]

There is nothing wrong with the call to XtGetCG above, As we have discussed
before Joel you cannot change the attributes in a GC created with XtGetGC.
(e.g. XSetForground() is a NO NO).  But there is nothing wrong with specifying
values in the call to XtGetGC().

Right:

myXGCV.foreground = WhitePixel(dpy, DefaultScreen(dpy));
myXGCV.background = BlackPixel(dpy, DefaultScreen(dpy));
valuemask = GCForeground | GCBackground;
gc = XtGetGC(Widget, valuemask, &myXGCV);

Right:
gc = XCreateGC(XtDisplay(w), XtWindow(w), 0L, &values);
XSetFunction(XtDisplay(w), gcCopy, GXinvert);
XSetPlaneMask(XtDisplay(w), gcCopy, foreground ^ background);
XSetForeground(XtDisplay(w), gcCopy, AllPlanes);

Wrong:

gc = XtGetGC(w, 0L, &values);
XSetFunction(XtDisplay(w), gcCopy, GXinvert);
XSetPlaneMask(XtDisplay(w), gcCopy, foreground ^ background);
XSetForeground(XtDisplay(w), gcCopy, AllPlanes);



I hope this clears up any confusion.

						Chris D. Peterson     
						MIT X Consortium /
						Project Athena 

Net:	kit@athena.mit.edu		
Phone: (617) 253 - 1326			
USMail: MIT - Room E40-321
	77 Massachusetts Ave.		
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