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From: vrenjak@rm1.UUCP (Milan Vrenjak)
Newsgroups: comp.windows.x
Subject: Re: XDrawRectangle w/ negative width/height?
Message-ID: <1014@rm1.UUCP>
Date: 8 Feb 91 02:26:47 GMT
References: <2124@cs.rit.edu>
Sender: news@rm1.UUCP
Reply-To: vrenjak@rm1.UUCP (Milan Vrenjak)
Organization: Racal-Milgo, Sunrise, Florida
Lines: 37

In article <2124@cs.rit.edu>, mxh5795@cs.rit.edu (Michael X Houwers) writes:
|> 
|> 
|> 
|> The strange behavior I noticed came when I attempted to rubberband a
|> rectangle in any direction which would cause the width or height to
|> be negative.  If this happened, it appeared that a small corner of
|> the old rectangle (I am using GXxor to draw over the old rectangle)
|> is not getting redrawn correctly.  So as a result, there are lots
|> of small corners of rectangles running around the screen.
|> 
|> I looked at the Xlib Reference Manual (from O'Reilly) and found
|> no caveats regarding a negative width and/or height.
|> 
|> So, the question is:  can you specify a negative width or height for
|> a rectangle with no unexpected side effects, and, if that is legal,
|> are there any known bugs when doing this?
|> 
|> Any help would be greatly appreciated..
|> 
|> Thanks,
|> mike houwers
|> --

I found the same problem on Sun's sparcstation under X11R4.
Douglas Young's "The X Window System, Programming and Applications
with Xt (OSF/MOTIF Edition)" described that this scenario may
happend and inverted the x,y coordinates to make it positive.
As to why, this is all I got from p277 -

	"Some X servers do not draw polygonal figures correctly if the
	 second point is less than the first in either direction. The
	 auxillary function check_points() checks for this case
	 and reverses the coordinates if necessary." 
		... and shows this function

Hope this helps