func TriangleIntersection(V1, V2, V3, O, D mgl.Vec3) (out float32, hit bool) {
const EPSILON = 0.000001
var e1, e2 mgl.Vec3 //Edge1, Edge2
var P, Q, T mgl.Vec3
var det, inv_det, u, v, t float32
//Find vectors for two edges sharing V1
e1 = V2.Sub(V1)
e2 = V3.Sub(V1)
//Begin calculating determinant - also used to calculate u parameter
P = D.Cross(e2)
//if determinant is near zero, ray lies in plane of triangle
det = e1.Dot(P)
//NOT CULLING
if det > -EPSILON && det < EPSILON {
return 0, false
}
inv_det = 1 / det
//calculate distance from V1 to ray origin
T = O.Sub(V1)
//Calculate u parameter and test bound
u = T.Dot(P) * inv_det
//The intersection lies outside of the triangle
if u < 0 || u > 1 {
return 0, false
}
//Prepare to test v parameter
Q = T.Cross(e1)
//Calculate V parameter and test bound
v = D.Dot(Q) * inv_det
//The intersection lies outside of the triangle
if v < 0 || u+v > 1 {
return 0, false
}
t = e2.Dot(Q) * inv_det
if t > EPSILON { //ray intersection
return t, true
}
// No hit, no win
return 0, false
}
func (m *HeightMap) Normal(x int, y int) mgl.Vec3 {
l := x - 1
r := x + 1
b := y - 1
t := y + 1
hi := m.Get(x, y)
lh := m.Get(l, y) - hi
rh := m.Get(r, y) - hi
bh := m.Get(x, b) - hi
th := m.Get(x, t) - hi
v1 := mgl.Vec3{1, 0, rh}.Normalize()
v2 := mgl.Vec3{0, 1, th}.Normalize()
v3 := mgl.Vec3{-1, 0, lh}.Normalize()
v4 := mgl.Vec3{0, -1, bh}.Normalize()
n1 := v1.Cross(v2).Normalize()
n2 := v2.Cross(v3).Normalize()
n3 := v3.Cross(v4).Normalize()
n4 := v4.Cross(v1).Normalize()
return n1.Add(n2).Add(n3).Add(n4).Normalize()
}
