func (b *body) setMaterial(mass, bounciness float64) *body {
b.imass = 0 // static unless there is mass.
if !lin.AeqZ(mass) {
b.imass = 1.0 / mass // only need inverse mass
b.iit = b.shape.Inertia(mass, b.iit) // shape inertia
if lin.AeqZ(b.iit.X) { // inverse shape inertia
b.iit.X = 0
} else {
b.iit.X = 1.0 / b.iit.X
}
if lin.AeqZ(b.iit.Y) {
b.iit.Y = 0
} else {
b.iit.Y = 1.0 / b.iit.Y
}
if lin.AeqZ(b.iit.Z) {
b.iit.Z = 0
} else {
b.iit.Z = 1.0 / b.iit.Z
}
}
b.restitution = bounciness
b.movable = b.imass != 0
return b
}
// castRayPlane calculates the point of collision between ray:a and
// plane:b. The contact point is returned if there is an intersection.
func castRayPlane(a, b Body) (hit bool, x, y, z float64) {
sa, sb := a.Shape().(*ray), b.Shape().(*plane)
la, lb := a.World().Loc, b.World().Loc
rdir := b.(*body).v0.SetS(sa.dx, sa.dy, sa.dz).Unit() // ray direction.
nrm := a.(*body).v0.SetS(sb.nx, sb.ny, sb.nz).Unit() // plane normal.
nrm.MultQ(nrm, b.World().Rot) // apply world spin to plane normal.
denom := rdir.Dot(nrm)
if lin.AeqZ(denom) || denom < 0 {
return false, 0, 0, 0 // plane is behind ray or ray is parallel to plane.
}
// calculate the difference from a point on the plane to the ray origin.
dx, dy, dz := rdir.X, rdir.Y, rdir.Z
diff := b.(*body).v0.SetS(lb.X-la.X, lb.Y-la.Y, lb.Z-la.Z)
dlen := diff.Dot(nrm) / denom
if dlen < 0 {
return false, 0, 0, 0
}
// Get contact point by scaling the ray direction with the contact distance
// and adding the ray origin.
x, y, z = dx*dlen+la.X, dy*dlen+la.Y, dz*dlen+la.Z
return true, x, y, z
}