From: airey@woof.asd.sgi.com (John Airey)
Newsgroups: comp.sys.sgi.graphics
Subject: Re: Esoteric Texture Question(s)
Date: 19 Dec 92 03:38:53 GMT
Organization: Silicon Graphics, Inc.  Mountain View, CA
NNTP-Posting-Host: woof.asd.sgi.com


In article <BzHIAv.I5q@news.iastate.edu>, boylan@pi.eai.iastate.edu writes:
> The following are a couple of irritatingly specific GL questions,
> primarily directed towards the GL development engineers at SGI:
> 
> FIRST QUESTION:
> 
> I'm guessing it's not possible right now, but it seems to me that it would
> be really nice to somehow automatically generate high-frequency noise.
> 
> This would allow you to get close to textures (even low-resolution ones)
> without getting the annoying "out-of-focus" viewer phenomenon.
> 
> Someone said that there are plans for allowing for combinations of two
> textures at the same time.  Is this true?  This would be a nice general
> solution for the high-freq noise problem and would also work well for
> times when you want to have (for example) a shiny reflection-mapped wooden
> sphere.

   See DETAIL textures on the RealityEngine. It's not completely general 
   because only one set of texture coordinates are supplied, so the
   application  of the DETAIL texture and the base texture have to be 
   related. (you do have some control over relative scale and the amount
   of detail texture applied at a given LOD).

> 
> SECOND QUESTION:
> 
> Is there anyway to do TX_POINT texture interpolation on the alpha channel
> (I want 0's and 255's, but nothing in-between) and TX_BILINEAR interpolation
> for RGB components of a texture map?  I'm generating a field of trees using

   On the RealityEngine you can
     TX_MAGFILTER_COLOR, TX_BILINEAR
     TX_MAGFILTER_ALPHA, SHARPEN 
     which will do better than what you want.

> tree textures mapped onto polygons.  I'm using afunction() to disable the
> drawing of pixels with alpha of zero.  (Please don't tell me to sort the 
> forest in back-to-front-order -- that's cheating!)
> 
> It would be nice if you could do a afunction(255,AF_EQUAL) or
> afunction(0,AF_GREATER), but you can't.  The only real options
> are afunction(0,AF_NOTEQUAL) (don't draw 0-alpha pixels) and
> afunction(0,ALWAYS) (the default).

  you get the full range of AF_EQUAL,NOTEQUAL,LESS,LEQUAL, etc. on 
  VGXT and RealityEngine. I think we forgot to document it for a while.

> 
> 
> Thanks a million-lighted-z-buffered-textured-polygons-per-second,
> 

  De nada.

> Narret J. Nalyob
> 
> 
> P.S.  Still waiting for the hardware support for FFD's (Or was it
> FFT's?), jpeg_lrectwrite(), and Phong-shaded bump-maps.  ;^)

  Hmm. Don't have exactly that but check out 4.0.5G and IL 2.0. on RE.

  Can you say, "convolve a 1 comp image with 5x5 separable kernel at
  20 _Million_ pixels/sec"?
> 
> -- 
> Terran J. Boylan, Sr. Artist/Programmer | "It's better to have loved
> Engineering Animation, Inc.,  Ames, IA  | and lost than just to have
> (515) 296-9908 / (515) 296-7934 (> 5PM) | lost." -- Dorky Dog
                
john m. airey      airey@asd.sgi.com  (415) 390-5248
                   M/S 7U-550 Silicon Graphics, Advanced Graphics Division
                   2011 N. Shoreline Blvd., Mtn. View, CA 94039