Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!helios!inetg1!dprmjc
From: dprmjc@prism.ARCO.COM (M. J. Cole)
Newsgroups: comp.sys.sgi
Subject: Re: quad strips bugs ?
Message-ID: <1991Apr29.141450.4737@Arco.COM>
Date: 29 Apr 91 14:14:50 GMT
References: <9104280445.AA10669@karron.med.nyu.edu>
Sender: dprmjc@prism (M. J. Cole)
Organization: ARCO Oil & Gas Company
Lines: 35

In article <9104280445.AA10669@karron.med.nyu.edu>, Dan Karron@UCBVAX.BERKELEY.EDU writes:
> 
> I am trying to use the bgnqstrip and endqstrip commands to draw
> filled squares.
> 
> I keep getting a figure that looks like it is starting at the
> local origin, then drawing my square, then returns to the origin.
> 
> I have worked around it by using the polygon functions, but
> I was wondering if this was a known problem. My data is good because
> I get the expected results from the poly calls. 
>

Two possible problems:  
  1) qstrips require a different vertex ordering than polygons. 
     For polygon: 1--2      For quadrilateral: 1--3
                  |  |                         |  |
                  0--3                         0--2  
     Quoting from page 2-27 of the Graphics Library Programming Guide: 
	"Note that the vertex order required by quad strips 
	 matches the order required for `equivalent' triangle 
	 meshes."

  2) If you are using lighting on a Personal Iris DO NOT USE triangle meshes
     or quadrilateral strips (weird things will happen).  This has been
     a "known bug" for so long, I wonder why they don't put a notice in
     the manuals. :-)

...............................................................................  
Mary J. Cole        ARCO Oil & Gas Company 
mjcole@arco.com     2300 W. Plano Parkway; PRC-D3239; 
(214)754-6857       Plano, TX 75075 
...............................................................................  
I'm continually AMAZED at th'breathtaking effects of WIND EROSION!! -ZIPPY
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