In article <3ee8ef8f$1@news.povray.org>,
 "Ray Gardener" <ray### [at] daylongraphicscom> wrote:

> What if... we limited the scene extents (in a seperate
> version of POV-Ray, of course) to some small volume
> like 1024 cubic units where single-precision floats
> would be more viable? One could only render small scenes
> or single objects, but when developing single objects
> (like people or cars), that's acceptable.

1024 units would probably still be a bit large. This has been done 
before, and is actually slower on modern systems (there was a thread 
about it recently on comp.graphics.rendering.raytracing). You go through 
a lot of contortions to get it to work, and get a more limited, lower 
quality, slower renderer as a result. Now do you see why?


> The Tachyon raytracer
> http://jedi.ks.uiuc.edu/~johns/raytracer/
> has an option to build using
> single precision (I imagine typedef'ing POV's DBL type
> to float instead of double would be analogous), and
> its author reports a 5-20% speed increase even without
> hardware leveraging. He had to customize his epsilon
> constants but I think it shows that using single precision
> is possible. If I was modeling a chair or whatever,
> I wouldn't turn down any speed improvement, even if
> the occasional triangle had a gap.

> POV's bounding slab bbox are already single-precision,
> interestingly. BBOX_VAL is type SNGL.

Yes, so are mesh vertices. In the former case, precision errors are 
relatively unimportant. In the second case, it is a matter of practical 
storage of large meshes, made possible by the fact that the intersection 
calculations don't stress the precision much. There are other objects 
that strain the limits of double precision, Tachyon only has spheres, 
infinite planes, triangles, rings, cylinders, boxes, a kind of 
internally generated fractal height field which is tessellated to a 
mesh, quadrics, voxels. Probably the most precision-requiring one is the 
generic quadric, a second-order surface. POV supports generic cubics 
(third order), toruses and generic quartics (which are fourth-order), 
and generic polynomial shapes up to 7th order. Also, blobs, julia 
fractals, lathe/sor, prism, sphere sweeps, superellipsoids...you get the 
idea.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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