Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!samsung!munnari.oz.au!metro!usage.csd.unsw.oz.au!sphinx!pta!yarra!melba.bby.oz.au!gnb
From: gnb@bby.oz.au (Gregory N. Bond)
Newsgroups: comp.windows.x
Subject: BUG: XtSetValues assumes all non-widgets are RectObjs
Message-ID: <1991Apr17.073327.12784@melba.bby.oz.au>
Date: 17 Apr 91 07:33:27 GMT
Sender: usenet@melba.bby.oz.au (news READER id)
Organization: Burdett, Buckeridge and Young Ltd.
Lines: 77
Nntp-Posting-Host: leo-gw

[This has been sent to xbugs]

			  X Window System Bug Report
			    xbugs@expo.lcs.mit.edu


VERSION:
    R4, MIT tape patched to fix-18

CLIENT MACHINE and OPERATING SYSTEM:
	Any

DISPLAY TYPE:
	Any

WINDOW MANAGER:
	Any

AREA:
	Xt

SYNOPSIS:
	XtSetValues assumes all non-widget objects are RectObjs

DESCRIPTION: 
	The XtSetValues handling of redraws is flawed for Objects that
	are not widgets and not subclasses of RectObj.  When a widget
	set_values routine returns True, XtSetValues forces a redraw
	by doing an XClearArea on the widget window.  If the object is
	not a widget, XtSetValues finds the nearest widget ancestor
	and, treating the object as a RectObj, clears the portion of
	the ancestor window that is "covered" by the RectObj.  If the
	object is not a RectObj, this will be wrong and a random part
	of the window will be cleared.  If the data wrongly read as
	the rectangle coords is sufficiently perverse, a BadValue
	error may be generated (I think, I've not actually seen one).

	It doesn't seem to be actually causing any problems for me,
	but perhaps I am just lucky with the data I have in the
	"rectangle" fields (they overlap 2 Pixel values and an integer
	in the subclass I am using, which means XtSetValues was seing
	x=<small number>, y=0, 	width=<small number>, height=0,
	borderwidth=0).  

	It is not clear what the correct action is in this case.  One
	approach is to generate a synthetic expose event on the window
	with an empty region.  The fix below handles it by just not
	doing any redraws for changes on non-RectObj objects.
	Whatever is chosen will need to be documented!

REPEAT BY:
	Examine the source code!

SAMPLE FIX:
   *** SetValues.c.DIST    Wed Apr 17 17:16:24 1991
   --- SetValues.c Wed Apr 17 17:17:35 1991
   ***************
   *** 262,268 ****
		 if (redisplay && XtIsRealized(w) && !w->core.being_destroyed)
		     XClearArea (XtDisplay(w), XtWindow(w), 0, 0, 0, 0, TRUE);
	     } else { /*non-window object */
   !         if (redisplay && ! cleared_rect_obj ) {
		 Widget pw = _XtWindowedAncestor(w);
		 if (XtIsRealized(pw) && !pw->core.being_destroyed) {
		     RectObj r = (RectObj)w;
   --- 262,268 ----
		 if (redisplay && XtIsRealized(w) && !w->core.being_destroyed)
		     XClearArea (XtDisplay(w), XtWindow(w), 0, 0, 0, 0, TRUE);
	     } else { /*non-window object */
   !         if (XtIsRectObj(w) && redisplay && ! cleared_rect_obj ) {
		 Widget pw = _XtWindowedAncestor(w);
		 if (XtIsRealized(pw) && !pw->core.being_destroyed) {
		     RectObj r = (RectObj)w;
--
Gregory Bond, Burdett Buckeridge & Young Ltd, Melbourne, Australia
Internet: gnb@melba.bby.oz.au    non-MX: gnb%melba.bby.oz@uunet.uu.net
Uucp: {uunet,pyramid,ubc-cs,ukc,mcvax,prlb2,nttlab...}!munnari!melba.bby.oz!gnb