Compiling triangle intersection code?

0
votes

My Google-fu has only turned up one result that returns the point of intersection between a ray and a triangle: http://geomalgorithms.com/a06-_intersect-2.html

And I am having absolutely no luck compiling it. I have done this for the points/vectors:

typedef struct {
    float x, y, z;
} Vector;
typedef struct {
    float x, y, z;
} Point;
typedef struct {
    Vector P0, P1;
} Ray;
typedef struct {
    Point V0, V1, V2;
} Triangle;

And then it throws errors about this code:

u = T.V1 - T.V0;
v = T.V2 - T.V0;
n = u * v;

"No match for operator - (operand types are Point and Point)"

So then I rewrote all of the code to be like this:

u.x=T.V1.x-T.V0.x;
u.y=T.V1.y-T.V0.y;
u.z=T.V1.z-T.V0.z;
v.x=T.V2.x-T.V0.x;
v.y=T.V2.y-T.V0.y;
v.z=T.V2.z-T.V0.z;
n.x=u.x*v.x;
n.y=u.y*v.y;
n.z=u.z*v.z;

But it still says the ray { 3, 1, -3 } { 3, -1, -3 } is not inside the triangle { -10, 0, -10 } { 10, 0, 10 } { 10, 0, -10 }. I checked this in Blender, though, and the ray indeed intersects the triangle.

Can anyone please point out what I'm doing incorrectly, or link to another page with a function that will return the exact point where a line segment intersects a triangle? I would rather do this in C than have to link some vector library. Thank you!

2
c++ccollision-detectionraytracing
possible duplicate of Operator overloading – Cory Kramer
You need to define your arithmetic operators for example operator+, operator-, etc. – Cory Kramer
@SouravGhosh: T is obviously a Triangle. – TonyK
@TonyK I don't see how it is obvious to you. I have seen thousands of mistakes caused by this obvious belief. And yes, that "hehe" part in my comment is a typo, it should read here. – Sourav Ghosh
just for curiosity: Aren't there 2 intersection points? – 463035818_is_not_a_number

2 Answers

1
votes

Here is the problem:

n = u * v;

This has to be interpreted as the vector product n = u x v, not component-wise multiplication.

0
votes

I believe the author of the page did not intend to publish valid out-of-the-box C++ there, as hinted by the quotes he used to write the name of the language. To turn that pseudocode into compilable code, you would need to implement a few operators yourself, such as the cross product of two 3D vectors (this is trivial, by the way).

Assume that classes are already given for the objects: ...