三角形跟射线求交

/*!	V0，V1，V2三角形三顶点
I为交点
返回值	-1：没有交点
0：	交点在三角形外
1：交点在三角形内部
*/
int intersect_RayTriangle( const gtl::Rayf& R,
const gtl::Vec3f& V0, const gtl::Vec3f& V1, const gtl::Vec3f& V2,
gtl::Vec3f& I )
{
gtl::Vec3f    u, v, n;             // triangle vectors
gtl::Vec3f    dir, w0, w;          // ray vectors
float     r, a, b;             // params to calc ray-plane intersect

// get triangle edge vectors and plane normal
u = V1 - V0;
v = V2 - V0;
n = u.cross(v);

if (n == gtl::Vec3f(0.0f, 0.0f, 0.0f))            // triangle is degenerate
return -1;                 // do not deal with this case

dir = R.getDirection();             // ray direction vector
w0 = R.getOrigin() - V0;

a = -( n.dot(w0) );
// a = -dot(n,w0);
b = n.dot(dir);
//b = dot(n,dir);
if (fabs(b) < SMALL_NUM) {     // ray is parallel to triangle plane
if (a == 0)                // ray lies in triangle plane
return 2;
else return 0;             // ray disjoint from plane
}

// get intersect point of ray with triangle plane
r = a / b;
if (r < 0.0)                   // ray goes away from triangle
return 0;                  // => no intersect
// for a segment, also test if (r > 1.0) => no intersect

I = R.getOrigin() + r * dir;           // intersect point of ray and plane

//// is I inside T?
float    uu, uv, vv, wu, wv, D;

uu = u.dot(u);
uv = u.dot(v);
vv = v.dot(v);
w = I - V0;
wu = w.dot(u);
wv = w.dot(v);
D = uv * uv - uu * vv;

// get and test parametric coords
float s, t;
s = (uv * wv - vv * wu) / D;
if (s < 0.0 || s > 1.0)        // I is outside T
return 0;
t = (uv * wu - uu * wv) / D;
if (t < 0.0 || (s + t) > 1.0)  // I is outside T
return 0;

return 1;                      // I is in T
}