55 lines
1.8 KiB
Rust
55 lines
1.8 KiB
Rust
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extern crate ria_weekend;
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use ria_weekend::{demo::Demo, ray, ray::Ray, vec3::Vec3};
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fn main() {
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let demo = Demo::new("surface_normal_sphere");
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let dimensions = demo.dimensions();
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let mut buf = String::new();
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// linear interpolation based on y coordinate
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// top to down
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let color = |ray: Ray| -> Vec3 {
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// center at z=-1. xy axis cuts sphere in half
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// blending parameter
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let t = ray_hit_sphere(Vec3::new(0.0, 0.0, 1.0), 0.5, &ray);
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if t > 0.0 {
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// For all rays that hit sphere, return red color
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// This will result in a sphere that is red in color
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let N = ray.point_at_parameter(t) - Vec3::new(0.0, 0.0, -1.0);
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return Vec3::new(N.x() + 1.0, N.y() + 1.0, N.z() + 1.0) * 0.5;
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}
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let unit_direction = ray.direction().unit_vector();
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// For rays that don't hit sphere, It'll paint the gradient as the background
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// Linear gradient depends on y
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let t = 0.5 * (unit_direction.y() + 1.0);
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// start color + end color
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Vec3::new(1.0, 1.0, 1.0) * (1.0 - t) + Vec3::new(0.0, 0.0, 0.0) * t
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};
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ray::create_ray_demo(&mut buf, dimensions, color);
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demo.save_as_ppm(buf);
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}
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fn ray_hit_sphere(center: Vec3, radius: f32, ray: &Ray) -> f32 {
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// dot(A + t*B - C, A + t*B - C) = R*R
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// when expanded we get
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// t * t * dot(B, B) + 2 * t * dot(B, A-C) + dot(A-C, A-C) - R*R = 0
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// A-C
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let ac = ray.origin() - center;
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let a = ray.direction().dot(&ray.direction());
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let b = 2.0 * ac.dot(&ray.direction());
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let c = ac.dot(&ac) - radius * radius;
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let discriminant = b * b - 4.0 * a * c;
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if discriminant >= 0.0 {
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// return quadratic root
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(-b + discriminant.sqrt()) / (2.0 * a)
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} else {
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-1.0
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}
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}
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