"Warp" <war### [at] tagpovrayorg>  wrote:
>   I have never read or thought about the details of raytracing a triangle,
> but the basic algorithm is:
> [...]
>   2. See if the intersection point is inside the boundaries defined by the
>      triangle (the first fast test is if t<0, then the ray did not hit the
>      triangle).
> [...]
>   I can't say right now how step 2 is implemented.

May I help?

You have the plane defined by three points A,B,C.
You also have the intersection of the ray and the plane at point P.

Now you simply try to represent P by a linear combination of (C-A) and (B-A):

P=u*(C-A)+v*(B-A)

If, and only if,
    a)  A,B,C are forming a plane, and
    b)  P lies in the plane
this equation has exactly one solution for u and v.

now simply compare, if u and v are between 0 and 1 (including). if so, P is
inside the triangle and the ray hits the triangle.

IIRC, there was a shortcut, to combine your step 1 and 2, to speed up some
calculations, but concerning the current time, I'm simply to lazy and tired to
look it up now ...

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