I disagree.  I think mip-mapping would be quite useful in a ray tracer.
Mip-mapping is a computationally cheap way to achieve great texture
anti-aliasing results.  In many situations, you'd need to shoot tons of AA
rays to achieve the same effect as mip-mapping.

The problem with applying mip-mapping to ray-tracing is that it requires the
knowledge of the ray differential.  With normal scan-line rendering, this is
easy to compute using perspective transformations.  However, in a ray tracer
it is much more difficult because rays can be reflected and refracted from
either flat or curved surfaces.

Check out this paper for a more in-depth discussion of mip-mapping and ray
differentials in the context of ray tracing:
http://graphics.stanford.edu/papers/trd/

-Nathan


"Thorsten Froehlich" <tho### [at] trfde> wrote...
> In article <3da59141$1@news.povray.org> , "Sascha Ledinsky"
> <sas### [at] opensyscoat> wrote:
>
> > does anyone know a compile/patch for pov that supports MIP-mapping for
> > image-maps or other types of interpolation than bilinear (bicubic would
be
> > nice).
> > Or the other way round: Is there a reason for mip-mapping isn't
supported (I
> > think every $100 graphics card can do it ;-)
>
> Because mip-mapping is pointless for a ray-tracer?  In essence the only
need
> for mip-mapping is to reduce artifacts when there is no anti-aliasing or
> anti-aliasing is very hard to do and interpolation of the image is out of
> the question as well.  This is the case for Z-buffer based renderers like
> your $100 graphics card, but not for POV-Ray.  The gain from using
> mip-mapping in POV-Ray would be zero as far as quality is concerned.
>
>     Thorsten
>
> ____________________________________________________
> Thorsten Froehlich, Duisburg, Germany
> e-mail: tho### [at] trfde
>
> Visit POV-Ray on the web: http://mac.povray.org

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