heavens 0.4.5

N-body GPU simulations with rendering
Documentation 
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use nalgebra::{Matrix4, Rotation3, Unit, Vector3};

#[derive(Copy, Clone, Debug)]
pub struct Camera {
    eye_position: Vector3<f32>,
    target_position: Vector3<f32>,
    upward_direction: Unit<Vector3<f32>>,

    fov_y: f32,
    aspect_ratio: f32, // Width / height
    near_clip: f32,
    far_clip: f32,

    zoom: f32,
}

impl Camera {
    pub fn new(eye_position: [f32; 3], target_position: [f32; 3], fov_x: f32, zoom: f32) -> Self {
        debug_assert!(fov_x > 0.0);
        debug_assert!(zoom > 0.0);

        let aspect_ratio = 16.0 / 16.0;
        let fov_y = fov_x * aspect_ratio;
        let near_clip = 0.1;
        let far_clip = 1.0e27;

        debug_assert!(near_clip < far_clip);

        Self {
            eye_position: Vector3::from(eye_position),
            target_position: Vector3::from(target_position),
            upward_direction: Vector3::z_axis(),
            fov_y,
            aspect_ratio,
            near_clip,
            far_clip,
            zoom,
        }
    }

    pub fn as_slice(&self) -> Vec<f32> {
        let mut slice = ((self.look_at() * self.perspective()).transpose().as_slice()).to_vec();
        slice.push(self.zoom);
        slice.push(self.zoom);
        slice.push(self.zoom);
        slice.push(self.zoom);

        slice
    }

    pub fn rotate_azimuthal(&mut self, delta: f32) {
        let forward = (self.target_position - self.eye_position).normalize();
        let right = self.upward_direction.cross(&forward).normalize();
        let actual_up: Vector3<f32> = forward.cross(&right);
        let actual_up_dir = Unit::new_normalize(actual_up);

        let rotation = Rotation3::from_axis_angle(&actual_up_dir, delta);

        let new_forward = rotation * forward;
        self.target_position = self.eye_position + new_forward;
    }

    pub fn rotate_polar(&mut self, delta: f32) {
        let forward = (self.target_position - self.eye_position).normalize();
        let right = Unit::new_normalize(self.upward_direction.cross(&forward));

        let rotation = Rotation3::from_axis_angle(&right, -delta);

        let new_forward = rotation * forward;
        self.target_position = self.eye_position + new_forward;
    }

    pub fn magnify(&mut self, delta: f32) {
        self.zoom *= delta;
    }

    fn look_at(&self) -> Matrix4<f32> {
        let forward = (self.target_position - self.eye_position).normalize();
        let right = self.upward_direction.cross(&forward).normalize();
        let actual_up = forward.cross(&right).normalize();

        let rotation = Matrix4::new(
            right.x,
            actual_up.x,
            forward.x,
            0.0,
            right.y,
            actual_up.y,
            forward.y,
            0.0,
            right.z,
            actual_up.z,
            forward.z,
            0.0,
            0.0,
            0.0,
            0.0,
            1.0,
        );

        let translation = Matrix4::new(
            1.0,
            0.0,
            0.0,
            -self.eye_position.x,
            0.0,
            1.0,
            0.0,
            -self.eye_position.y,
            0.0,
            0.0,
            1.0,
            -self.eye_position.z,
            0.0,
            0.0,
            0.0,
            1.0,
        );

        rotation * translation
    }

    fn perspective(&self) -> Matrix4<f32> {
        let f = 1.0 / (self.fov_y / 2.0).tan();
        let nf = 1.0 / (self.near_clip - self.far_clip);

        Matrix4::new(
            f / self.aspect_ratio,
            0.0,
            0.0,
            0.0,
            0.0,
            f,
            0.0,
            0.0,
            0.0,
            0.0,
            (self.far_clip + self.near_clip) * nf,
            2.0 * self.far_clip * self.near_clip * nf,
            0.0,
            0.0,
            -1.0,
            0.0,
        )
    }
}