Re: [Plib-devel] texture repeating

[Steve B. <sjb...@ai...>]

Amit Bakshi wrote:
> 
> > Just for fun, is there an easy way to turn off mipmap generation in
> > ssg?  Perhaps for lower end cards I could just give the user a chance
> > to choose their poison ...

> I was under the impression that mipmapping does in fact speed up
> the rasterization of "far away" textured objects.

That's true under certain circumstances.

However, GL_LINEAR_MIPMAP_LINEAR requires you to read EIGHT texels
for every pixel on the screen where GL_NEAREST requires only one -
and perhaps the cache benefit vanishes under those circumstances...
so it depends somewhat on which mode you pick.

Anyway, Curt's concern is more as a way to try to control
the blurriness that's evident with MIPmapping of polygons that are
edge on - and which have strong features in the direction of foreshortening.

> This is due to the cache
> misses a full size texture would have when the texel/pixel ration gets high.

Yes - exactly.  The smaller MIPmaps come closer to fitting into the texture
hardware's cache.  For some devices (eg the Intel I810 cards that store
textures in main memory and fetch them via AGP) the effect is dramatic -
for others (like the older Voodoo's that don't have texture cache), there
is no effect.

> In fact you'll see some drivers that auto-generate mipmapped textures
> agains your will ( some NVidia drivers do/did that under Win32 ).

Hmmm - that's unacceptable IMHO.
 
-- 
Steve Baker   HomeEmail: <sjb...@ai...>
              WorkEmail: <sj...@li...>
              HomePage : http://web2.airmail.net/sjbaker1
              Projects : http://plib.sourceforge.net
                         http://tuxaqfh.sourceforge.net
                         http://tuxkart.sourceforge.net
                         http://prettypoly.sourceforge.net