Am 20.09.2012 15:36, schrieb Dabear:
> Hello guys,
>
> i came around the documentation site
> http://www.povray.org/documentation/view/3.6.1/348/
> and it says: "Adding reflection to a texture makes it take longer to render
> because an additional ray must be traced."
> I am wondering why it would take longer if i specify "reflection {1}". I always
> thought that you are then able to instantly calculate in which direction the ray
> must go and then just take the first objects color which is hit by the reflected
> ray. If you have some diffuse object then you must send out many rays in
> different directions to find out the color at the specific point and even then
> it can be inaccurate.
>
> Did i get something wrong?

Yes, you did: Diffuse surfaces are, by default, not computed by shooting 
hundreds or thousands of secondary rays around the scene, but by 
shooting rays towards the light sources only in order to determine 
shadowing. (A reflective surface just takes a single secondary ray, but 
that one will typically hit a diffuse surface, so the diffuse stuff is 
virtually always there.)

If you use radiosity, then for diffuse surfaces POV-Ray does indeed 
shoot hundreds or thousands of secondary rays around the scene, but only 
for some samples on the surface, which are then weighted and averaged 
for any points in between.

(And yes, radiosity is still slower than reflections indeed.)

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