> If you do not provide a surface normal, POV-Ray has to compute one for you.
> If both sides of the triangle mesh are to be lit and textured equally, the
> direction of the surface normal does not matter. However, if you want
> POV-Ray to apply different texturing or lighting to the backface and
> frontface, it needs more information such that all normals point in the same
> direction.
> 
> In order to let POV-Ray do this, you have to provide all triangle vertices
> in the same order.  Either clockwise or counterclockwise, it does not matter
> which order, just that they all have the same order.
> 
> This is the *only* way POV-Ray can compute a surface normal that always
> points in the same direction.  Once all your triangle vertices are specified
> in the same order, the surface normal will be well-defined and POV-Ray can
> correctly apply the backface and frontface texture.
> 

You are right, but it is a pity that the manual is not clear on that 
point ! (I looked again, nowhere what you says is said in the doc)

Moreover, I found there must be a bug in my normal vector (I do have 
some), because when I remove them the front and back side are OK (the 
order of vertices gives a correct orientation because the same order is 
used under OpenGL)

However, OpenGL never uses normal for orientation, so I could not see my 
bug under OpenGL, and discovered it when I exported pov files.

Anyway a big thanks for your help. Your "aggressive" (a bit ;-) 
discourse let me think that you must be right and I must be wrong and 
the discovered that I had a bug ...

Again,  it is a pity that the manual is not clear on that point ! 
because I would not have had doubt if the manual was clear.

Now I just need to find the bug in my code and fix it !

Post a reply to this message