On 12/12/2011 11:21 PM, clipka wrote:
> Yup. Except of course that the sky sphere has an infinite radius, while
> normal spheres have a finite one.

   Actually, technically speaking, a sky_sphere is a sphere of radius 1
which is centered at the origin of the current ray. It's just that it's 
evaluated only if the ray doesn't hit anything (thus making it only 
appear on the parts of the image where the nothingness of the background 
would otherwise be visible).

   A sky_sphere is also faster than a regular sphere because no actual 
ray-sphere intersection calculations are needed. (The color is taken 
from the sky_sphere just using the direction of the ray using simple math.)

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