0203-透明材质的反射

环境

• Time 2022-11-17
• WSL-Ubuntu 22.04
• Rust 1.65.0

前言

说明

参考：https://raytracing.github.io/books/RayTracingInOneWeekend.html

目标

实现透明材质的反射功能。

Dielectric

impl Dielectric {
    pub fn new(refraction: f64) -> Dielectric {
        Dielectric { refraction }
    }

    // 折射
    fn refract(uv: Vector3, n: Vector3, f: f64) -> Vector3 {
        let cos_theta = (-1.0 * uv).dot(n).min(1.0);
        let r = f * (uv + cos_theta * n);
        r - (1.0 - r.dot(r)).abs().sqrt() * n
    }

    fn reflectance(cosine: f64, ref_idx: f64) -> f64 {
        let r0 = ((1.0 - ref_idx) / (1.0 + ref_idx)).powi(2);
        r0 + (1.0 - r0) * (1.0 - cosine).powi(5)
    }
}

Material

impl Material for Dielectric {
    fn scatter(&self, ray: &Ray, record: &HitRecord) -> Option<(Color, Ray)> {
        let ratio = match record.face {
            true => 1.0 / self.refraction,
            false => self.refraction,
        };

        let normal = record.normal;
        let direction = ray.direction().unit();
        let cos = (-1.0 * direction).dot(normal).min(1.0);
        let sin = (1.0 - cos.powi(2)).sqrt();

        let mut rand = rand::thread_rng();
        let cannot_refract = ratio * sin > 1.0;
        let will_reflect = Self::reflectance(cos, ratio) > rand.gen();

        let direction = match cannot_refract || will_reflect {
            true => direction - 2.0 * direction.dot(normal) * normal,
            false => Self::refract(direction, normal, ratio),
        };

        let scattered = Ray::new(record.point, direction);
        Some((Color::new(1.0, 1.0, 1.0), scattered))
    }
}

main.rs

use std::rc::Rc;

use camera::Camera;
use hittable::{Hit, World};
use material::{Lambert, Metal};
use rand::Rng;
use ray::Ray;
use sphere::Sphere;
use vector3::{Color, Point3};

use crate::material::Dielectric;

mod camera;
mod hittable;
mod material;
mod ray;
mod sphere;
mod vector3;

fn main() {
    // 图片的比例，和宽高
    const WIDTH: u64 = 400;
    const HEIGHT: u64 = (WIDTH as f64 / camera::RATIO) as u64;
    const SAMPLES_PER_PIXEL: u64 = 100;
    const MAX_DEPTH: u64 = 50;

    // 相机
    let camera = Camera::new();

    // 输出图片，第一行输出 P3，表示像素图
    let mut content = String::from("P3");
    // 输出宽和高，和最大颜色值
    content.push_str(&format!("\n{WIDTH} {HEIGHT}\n255\n"));

    let ground = Rc::new(Lambert::new(Color::new(0.8, 0.8, 0.0)));
    let center = Rc::new(Lambert::new(Color::new(0.1, 0.2, 0.5)));
    let left = Rc::new(Dielectric::new(1.5));
    let left2 = Rc::new(Dielectric::new(1.5));
    let right = Rc::new(Metal::new(Color::new(0.8, 0.6, 0.2), 0.0));

    let world: World = vec![
        Box::new(Sphere::new(Point3::new(0.0, -100.5, -1.0), 100.0, ground)),
        Box::new(Sphere::new(Point3::new(0.0, 0.0, -1.0), 0.5, center)),
        Box::new(Sphere::new(Point3::new(-1.0, 0.0, -1.0), 0.5, left)),
        Box::new(Sphere::new(Point3::new(-1.0, 0.0, -1.0), -0.4, left2)),
        Box::new(Sphere::new(Point3::new(1.0, 0.0, -1.0), 0.5, right)),
    ];

    let mut rng = rand::thread_rng();
    for j in (0..HEIGHT).rev() {
        // 进度
        eprintln!("Scan lines remaining: {j}");
        for i in 0..WIDTH {
            let mut color = Color::default();
            for _ in 0..SAMPLES_PER_PIXEL {
                let random_u: f64 = rng.gen();
                let random_v: f64 = rng.gen();

                let u = ((i as f64) + random_u) / ((WIDTH - 1) as f64);
                let v = ((j as f64) + random_v) / ((HEIGHT - 1) as f64);

                color += ray_color(&camera.get_ray(u, v), &world, MAX_DEPTH);
            }
            content.push_str(&color.format_str(SAMPLES_PER_PIXEL as f64));
        }
    }
    println!("{}", content);
    eprintln!("Done.");
}

// 光线的颜色计算
fn ray_color(ray: &Ray, hittable: &dyn Hit, depth: u64) -> Color {
    // 超过最大深度，直接变成黑色
    if depth == 0 {
        return Color::new(0.0, 0.0, 0.0);
    }

    // 射线命中物体
    if let Some(record) = hittable.hit(ray, 0.001, f64::INFINITY) {
        // 命中物体根据材料散射光线
        return match record.material.scatter(ray, &record) {
            Some((attenuation, scattered)) => {
                attenuation * ray_color(&scattered, hittable, depth - 1)
            }
            None => Color::new(0.0, 0.0, 0.0),
        };
    }

    // 射线未命中，射线的单位向量
    let unit = ray.direction().unit();
    // 因为需要得到上下渐变的背景图，所以需要对 y 进行插值。
    let t = 0.5 * (unit.y + 1.0);
    // 线性插值，根据不同的光线得到在下面这个范围里的不同的颜色，并且是渐变色。
    (1.0 - t) * Color::new(1.0, 1.0, 1.0) + t * Color::new(0.5, 0.7, 1.0)
}

效果

总结

新增了反射功能。

附录