Re: NEED HELP ON TEXTURE MAPPING!
Angus Dorbie (dorbie++at++sgi.com)
Fri, 03 Jul 1998 11:59:44 -0700
Andreas.Ekstrand++at++saab.se wrote:
>
> Hello!
>
> I have a problem trying to map satellite textures on an ASD
> terrain mesh. I have also observed this problem when mapping
> textures on an "ordinary" static terrain mesh. The polygons
> match perfectly so the texture mapping must be the problem.
> The texture images themselves also match perfectly when I
> watch them unmapped. But as soon as Performer maps them on
> to the polygons there is disturbance between these texture
> pieces.
>
> My satellite textures are 2048x2048 each and between these
> pieces you can observe an annoying miscolored line when they
> are mapped. I figure this is due to Performer's method of
> interpolating, or blurring, the texture pixels to texels so
> they cover the whole surface. I have come the the conclusion
> (right or wrong?) that Performer filters the texture with some
> kind of average kernel, and that in the outer borders of the
> texture the pixels are blurred with the pixels on the opposite
> side of the image. This way unwanted lines with different colors
> appear between the texture pieces and in the outer borders of the
> terrain.
>
> Is there anyone who knows how this phenomenon can be avoided?
You need to clamp the textures. What you see is the texels on
the opposite side of the image wraping around. Clamping will
avoid this and look better although you won't get interpolation
across tiles and your MIP map levels need to be pre compute based
on the whole dataset instead of individual tiles for best effect.
So expect to see some _BIG_ improvements, but it still won't be
perfect, unless you use something like CLIP mapping.
Cheers,Angus.
--
"Only the mediocre are always at their best." -- Jean Giraudoux
For advanced 3D graphics Performer + OpenGL based examples and tutors:
http://www.dorbie.com/
=======================================================================
List Archives, FAQ, FTP: http://www.sgi.com/Technology/Performer/
Submissions: info-performer++at++sgi.com
Admin. requests: info-performer-request++at++sgi.com
This archive was generated by hypermail 2.0b2
on Mon Aug 10 1998 - 17:57:40 PDT