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From: rad@home.asd.sgi.com (Bob Drebin)
Newsgroups: comp.sys.sgi
Subject: Re: SGI VGX Texturing
Message-ID: <1991Feb28.172915.13853@odin.corp.sgi.com>
Date: 28 Feb 91 17:29:15 GMT
References: <9102271951.AA20115@taurus.cs.nps.navy.mil>
Sender: news@odin.corp.sgi.com (Net News)
Reply-To: rad@home.asd.sgi.com (Bob Drebin)
Organization: sgi
Lines: 41

You have to be careful when using scrsubdivide().  As noted in the man page:

     When the screen size of subdivided polygons is limited, either by minsize
     or by maxsize, adjacent polygons can subdivide differently such that
     newly created vertices on their shared boundary do not coincide.  In this
     case, some pixels at their shared boundary may not be scan converted by
     either polygon.

I can suggest two solutions: 

1)  Only use maxz to control subdivision.  Disable minsize and maxsize
    by setting them to zero.  This will prevent T-verticies from being 
    generated, which cause the pixel dropouts.  

2)  Use anti-aliased lines. Draw your scene using your current scrsubdivide
    parameters, then redraw the outlines of troublesome polygons using 
    anti-aliased lines.

    For example:
	/* draw the scene */
	zbuffer(TRUE);
	blendfunction(BF_ONE,BF_ZERO);
	scrsubdivide(SS_ON,myparms);
	draw_terrain();
	scrsubdivide(SS_OFF,myparms);
	draw_nontextured_stuff();

	/* redraw outlines of textured polys */
	blendfunction(BF_SA,BF_MSA);
	polymode(PYM_LINE);
	linesmooth(SML_ON);
	scrsubdivide(SS_ON,myparms);
	draw_terrain();		 


Hope this helps.

Bob Drebin, SGI

P.S.:  The function polysmooth does not work with textured polygons.  This
       is noted in its man page.