Path: utzoo!utgpu!news-server.csri.toronto.edu!orasis.vis.toronto.edu!culhane
Newsgroups: comp.sys.sgi
From: culhane@vis.toronto.edu (Sean Culhane)
Subject: Help needed with texture mapping images ...
Message-ID: <91May3.173736edt.8286@orasis.vis.toronto.edu>
Organization: Department of Computer Science, University of Toronto
Date: 3 May 91 21:37:56 GMT
Lines: 76


Hello, all.

A *BIG* thanks to all those who replied to my previous posting about
transforming images.  I seems that the overwhelming majority would
use texture mapping to do the job (given that one has a VGX).

Now, I am faced with another problem, and have banged my head for just
several hours and I am very dizzy.  Here's my situation:

I have an image (in the format that lrectwrite expects), and I do a


   texdef2d( 1, 2, ImageSize, ImageSize, Image, 5, texprops);
   texbind(TX_TEXTURE_0, 1);


The result is that I only get ONE CORNER of a 256x256 image mapped onto the
polygon.  So I look to the manual, and I read that the TX_TILE texture
property will support mapping of high-resolution images with multiple
rendering passes.  So, I've set up the following:


   float texprops1[] = {TX_MINFILTER, TX_BILINEAR,
   	 	     TX_MAGFILTER, TX_BILINEAR,
   		     TX_TILE, 0.0, 0.0, 0.5, 0.5,
   		     TX_NULL};
   float texprops2[] = {TX_MINFILTER, TX_BILINEAR,
   	 	     TX_MAGFILTER, TX_BILINEAR,
   		     TX_TILE, 0.5, 0.0, 1., 0.5,
   		     TX_NULL};
   float texprops3[] = {TX_MINFILTER, TX_BILINEAR,
   	 	     TX_MAGFILTER, TX_BILINEAR,
   		     TX_TILE, 0.0, 0.5, 0.5, 1.,
   		     TX_NULL};
   float texprops4[] = {TX_MINFILTER, TX_BILINEAR,
   	 	     TX_MAGFILTER, TX_BILINEAR,
   		     TX_TILE, 0.5, 0.5, 1., 1.,
   		     TX_NULL};


and the four texture definitions:

   texdef2d( 1, 2, ImageSize, ImageSize, Image, 10, texprops1); 
   texdef2d( 2, 2, ImageSize, ImageSize, Image, 10, texprops2); 
   texdef2d( 3, 2, ImageSize, ImageSize, Image, 10, texprops3); 
   texdef2d( 4, 2, ImageSize, ImageSize, Image, 10, texprops4); 


and I draw the polygon like so:


   for( i=1; i<=4; i++ ) {
      texbind(TX_TEXTURE_0, i);

      bgnpolygon();
         t2f(t0);  v3f(v0);
         t2f(t1);  v3f(v1);
         t2f(t2);  v3f(v2);
         t2f(t3);  v3f(v3);
      endpolygon();

   } /* for */


I am obviously mis-interpreting something here, since making these changes
causes the texture to be BLACK! (or non-existant ... who's to say).

Once again, and and all help/comments are greatly appreciated.

Sean.
--
Sean Culhane, Computer Vision Lab,  |"I know not with what weapons World War
Dept. of Computer Science,          | III will be fought, but World War IV
University of Toronto               | will be fought with sticks and stones."
culhane@{vis|ai|cs}.toronto.edu     |          -- Albert Einstein