In article <3974264c@news.povray.org>, Warp <war### [at] tagpovrayorg> 
wrote:

> John VanSickle <van### [at] erolscom> wrote:
> : For flat triangles the normal is derived from a cross-product of two
> : of the edge vectors (I presume) and therefore depends on the order the
> : vertices are defined.
> 
>   I think it doesn't matter which side the normal is pointing to (as in 
> any other surface in povray). This specially doesn't matter with 
> triangles since they do not have interior.

John VanSickle is right, the normal is derived using the cross-product 
of the edge vectors.(or something like that) The "up" side of the 
triangle is determined by the order of the vertices.
For lighting calculations, the normal is always flipped so it points to 
the side the intersecting ray came from, so you don't notice a 
difference. However, the real normal does matter if you are using 
MegaPOV and interior_texture. I am not aware of any other places where 
it matters...

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

Post a reply to this message