func (v Vec3) Dot2D(u Vec3) float32 {
	return v[0]*u[0] + v[2]*u[2]
}
func (v Vec3) Dot2D(u Vec3) float32 {
	return v[0]*u[0] + v[2]*u[2]
}
func ( v Vec3 ) Dot2D ( u Vec3 ) float32 { return v [ 0 ] * u [ 0 ] + v [ 2 ] * u [ 2 ] }
// Dot2D derives the dot product of two vectors on the xz-plane. u . v
//
// The vectors are projected onto the xz-plane, so the y-values are ignored.
Dot2D derives the dot product of two vectors on the xz - plane . u . v The vectors are projected onto the xz - plane so the y - values are ignored .