A function that create a ray from a perspective camera

ray_from_cam.rs

use cgmath::{Point2, Point3, Vector3, Vector4, Matrix4};
use cgmath::{SquareMatrix, InnerSpace};
use collision::{Ray, Ray3};

// http://antongerdelan.net/opengl/raycasting.html
fn ray_from_cam(proj: Matrix4<f32>, view: Matrix4<f32>, point: Point2<f32>) -> Ray3<f32> {
    assert!(point.x >= -1.0 && point.x <= 1.0);
    assert!(point.y >= -1.0 && point.y <= 1.0);

    // 4d Homogeneous Clip Coordinates
    let ray_clip = Vector4::new(point.x, point.y, -1.0, 1.0);

    // 4d Eye (Camera) Coordinates
    let ray_eye = proj.invert().unwrap() * ray_clip;
    let ray_eye = Vector4::new(ray_eye.x, ray_eye.y, -1.0, 0.0);

    // 4d World Coordinates
    let ray_world = (view.invert().unwrap() * ray_eye).truncate(); // into Vector3
    // don't forget to normalise the vector at some point
    let ray_world = ray_world.normalize();

    Ray::new(Point3::new(0.0, 0.0, 0.0), ray_world)
}