bevymouseray.rs

let ray = screen_to_world(cursor_position, &windows, camera, camera_transform);
let plane = HalfSpace::new(Unit::new_normalize(Vec3::Z.to_vector3()));
if let Some(toi) = plane.cast_local_ray(&ray, Real::MAX, false) {
    dbg!(ray.point_at(toi)); // <-- would expect values the same as bevy's units, but is instead y-1. to y1, and x-1.7 to x1.7 (I think this specific # has to do with the aspect ratio)
}

// From https://github.com/aevyrie/bevy_mod_raycast/blob/8b2ee7d015b9bb886684d7ad7796e404944bd5dd/src/primitives.rs
// MIT License
// Gets a ray from our camera to our mouse position on screen
pub fn screen_to_world(
    screen_position: Vec2,
    windows: &Res<Windows>,
    camera: &Camera,
    camera_transform: &GlobalTransform,
) -> Ray {
    let camera_position = camera_transform.compute_matrix();
    let window = windows
        .get(camera.window)
        .unwrap_or_else(|| panic!("WindowId {} does not exist", camera.window));
    let screen_size = Vec2::from([window.width() as f32, window.height() as f32]);
    let projection_matrix = camera.projection_matrix;

    // Normalized device coordinate cursor position from (-1, -1, -1) to (1, 1, 1)
    let cursor_ndc = (screen_position / screen_size) * 2.0 - Vec2::from([1.0, 1.0]);
    let cursor_pos_ndc_near: Vec3 = cursor_ndc.extend(-1.0);
    let cursor_pos_ndc_far: Vec3 = cursor_ndc.extend(1.0);

    // Use near and far ndc points to generate a ray in world space
    // This method is more robust than using the location of the camera as the start of
    // the ray, because ortho cameras have a focal point at infinity!
    let ndc_to_world: Mat4 = camera_position * projection_matrix.inverse();
    let cursor_pos_near: Vec3 = ndc_to_world.transform_point3(cursor_pos_ndc_near);
    let cursor_pos_far: Vec3 = ndc_to_world.transform_point3(cursor_pos_ndc_far);
    let ray_direction = cursor_pos_far - cursor_pos_near;
    Ray::new(
        cursor_pos_near.to_vector3().into(),
        ray_direction.to_vector3(),
    )
}