Well really what you'd want is anisotropic filtering. Take the 4 texture 
coordinates of 4 pixel centers and compute the true average of the texture 
within that quadrilateral region (though even a quadrilateral is an 
approximation). Obviously with pov's internal patterns a true average won't 
always be possible but you could adaptively sample the texture within that 
area far faster than you can adaptively anti-alias the image to get a 
similar quality result.

Mip maps save you from needing so many samples, but they also effectively 
bleed in colours from outside the sample area.

-- 
Tek
http://evilsuperbrain.com


"Zeger Knaepen" <zeg### [at] povplacecom> wrote in message 
news:438f9dee@news.povray.org...
I was searching for a possibility to do mipmapping in POV-Ray.

This one uses 11 different images (scaled 
800*800,400*400,200*200,100*100,50*50,25*25,12*12,6*6,3*3,2*2 and 1*1 
pixels) and interpolates between them in function of the distance from the 
camera and the angle of the surface (using an average between a spherical 
pattern and the aoi-pattern.

The scale of the spherical pattern is very resolution-dependant (a smaller 
output-image requires a smaller spherical-pattern), and as it is now it 
doesn't look good in reflections or refractions though.

Is there a reason that POV-Ray doesn't support it natively ?  I believe the 
reflection/refraction problem could be solved if I had access to the length 
of the ray from the camera to the object (being the sum of the lengthts of 
all recursive rays for that pixel... I seem to be having some trouble 
expressing myself in English lately :-/ ), and also the scale of the 
spherical pattern could be calculated automatically in function of the 
output-resolution.  Both things (I think) could easily be coded into POV-Ray 
(if you know how to program in C, which, unfortunately, I don't).

cu!
-- 
#macro G(b,e)b+(e-b)*C/50#end#macro _(b,e,k,l)#local C=0;#while(C<50)
sphere{G(b,e)+3*z.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1;
#end#end _(y-x,y,x,x+y)_(y,-x-y,x+y,y)_(-x-y,-y,y,y+z)_(-y,y,y+z,x+y)
_(0x+y.5+y/2x)_(0x-y.5+y/2x)            // ZK http://www.povplace.com

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