rustray/src/main.rs

use cgmath::prelude::*;

use cgmath::{vec3, vec4, InnerSpace, Matrix4, Point3, Vector3};

use image::ImageBuffer;
use utilities::prelude::*;

use std::f32::{consts::PI as M_PI, MAX};

struct Triangle {
    points: [Vector3<f32>; 3],
}

impl Triangle {
    pub fn new(v0: Vector3<f32>, v1: Vector3<f32>, v2: Vector3<f32>) -> Triangle {
        Triangle {
            points: [v0, v1, v2],
        }
    }
}

struct View {
    position: Vector3<f32>,
    look_at: Vector3<f32>,
    fov: f32,
}

fn main() {
    let input_data = [Triangle::new(
        vec3(0.0, 0.0, 0.0),
        vec3(1.0, 0.0, 0.0),
        vec3(1.0, 1.0, 0.0),
    )];

    let view = View {
        position: vec3(0.0, -4.0, 4.0),
        look_at: vec3(0.0, 0.0, 0.0),
        fov: 45.0,
    };

    let (origin, direction) = calculate_ray(640, 360, 1280, 720, &view);

    let color = pixel_color(origin, direction, &input_data);

    //debug_raytracer(1280, 720, &view, &input_data);
}

fn f_to_u(color: f32) -> u8 {
    ((color * 255.0) / 1.0) as u8
}

fn calculate_ray(
    x: u32,
    y: u32,
    dim_x: u32,
    dim_y: u32,
    view: &View,
) -> (Vector3<f32>, Vector3<f32>) {
    let aspect_ratio = dim_x as f32 / dim_y as f32;

    let p_x = (2.0 * ((x as f32 + 0.5) / dim_x as f32) - 1.0)
        * (view.fov / 2.0 * M_PI / 180.0).tan()
        * aspect_ratio;
    let p_y = (1.0 - 2.0 * (((dim_y - y) as f32 + 0.5) / dim_y as f32))
        * (view.fov / 2.0 * M_PI / 180.0).tan();

    let camera_to_world = Matrix4::look_at(
        Point3::from_vec(view.position),
        Point3::from_vec(view.look_at),
        vec3(0.0, 0.0, 1.0),
    )
    .inverse_transform()
    .unwrap();

    let origin = camera_to_world * vec4(0.0, 0.0, 0.0, 1.0);
    let direction = camera_to_world * vec4(p_x, p_y, -1.0, 1.0);

    (origin.truncate(), direction.truncate().normalize())
}

fn debug_raytracer(dim_x: u32, dim_y: u32, view: &View, data: &[Triangle]) {
    let mut imgbuf = ImageBuffer::new(dim_x, dim_y);

    for (x, y, pixel) in imgbuf.enumerate_pixels_mut() {
        let (origin, direction) = calculate_ray(x, y, dim_x, dim_y, view);

        let color = pixel_color(origin, direction, data);

        *pixel = image::Rgb([f_to_u(color.x), f_to_u(color.y), f_to_u(color.z)]);
    }

    imgbuf.save("raytrace.png").unwrap();
}

fn pixel_color(orig: Vector3<f32>, dir: Vector3<f32>, data: &[Triangle]) -> Vector3<f32> {
    let mut final_color = vec3(0.0, 1.0, 0.0);
    let mut closest_value = MAX;
    let mut closest_index = -1;

    for i in 0..data.len() {
        let v0 = data[i].points[0];
        let v1 = data[i].points[1];
        let v2 = data[i].points[2];
        let mut t = 0.0;

        if ray_triangle_intersect_naive(orig, dir, v0, v1, v2, &mut t) {
            if t < closest_value {
                closest_index = i as i32;
                closest_value = t;
            }
        }
    }

    if closest_index != -1 {
        final_color = vec3(1.0, 0.0, 0.0);
    }

    return final_color;
}

// source: https://www.scratchapixel.com/lessons/3d-basic-rendering/ray-tracing-rendering-a-triangle/moller-trumbore-ray-triangle-intersection
fn ray_triangle_intersect_mt(
    orig: Vector3<f32>,
    dir: Vector3<f32>,
    v0: Vector3<f32>,
    v1: Vector3<f32>,
    v2: Vector3<f32>,
    t: &mut f32,
) -> bool {
    let v0v1 = v1 - v0;
    let v0v2 = v2 - v0;
    let pvec = dir.cross(v0v2);
    let det = v0v1.dot(pvec);

    // ray and triangle are parallel if det is close to 0
    if det.abs() < 0.001 {
        return false;
    }

    let inv_det = 1.0 / det;

    let tvec = orig - v0;
    let u = tvec.dot(pvec) * inv_det;

    if u < 0.0 || u > 1.0 {
        return false;
    }

    let qvec = tvec.cross(v0v1);
    let v = dir.dot(qvec) * inv_det;

    if v < 0.0 || u + v > 1.0 {
        return false;
    }

    *t = v0v2.dot(qvec) * inv_det;

    true
}

fn ray_triangle_intersect_naive(
    orig: Vector3<f32>,
    dir: Vector3<f32>,
    v0: Vector3<f32>,
    v1: Vector3<f32>,
    v2: Vector3<f32>,
    t: &mut f32,
) -> bool {
    // compute plane's normal
    let v0v1 = v1 - v0;
    let v0v2 = v2 - v0;
    // no need to normalize
    let N = v0v1.cross(v0v2);
    let area2 = N.magnitude();

    // Step 1: finding P

    // check if ray and plane are parallel ?
    let NdotRayDirection = N.dot(dir);
    if NdotRayDirection.abs() < 0.001
    // almost 0
    {
        return false;
    } // they are parallel so they don't intersect !

    // compute d parameter using equation 2
    let d = N.dot(v0);

    // compute t (equation 3)
    *t = (N.dot(orig) + d) / NdotRayDirection;

    // check if the triangle is in behind the ray
    if *t < 0.0 {
        return false;
    } // the triangle is behind

    // compute the intersection point using equation 1
    let P = orig + *t * dir;

    // Step 2: inside-outside test
    let mut C; // vector perpendicular to triangle's plane

    // edge 0
    let edge0 = v1 - v0;
    let vp0 = P - v0;

    C = edge0.cross(vp0);
    if N.dot(C) < 0.0 {
        return false;
    } // P is on the right side

    // edge 1
    let edge1 = v2 - v1;
    let vp1 = P - v1;

    C = edge1.cross(vp1);
    if N.dot(C) < 0.0 {
        return false;
    } // P is on the right side

    // edge 2
    let edge2 = v0 - v2;
    let vp2 = P - v2;

    C = edge2.cross(vp2);
    if N.dot(C) < 0.0 {
        return false;
    } // P is on the right side;

    true // this ray hits the triangle
}