71 lines
1.9 KiB
Rust
71 lines
1.9 KiB
Rust
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use crate::scene_data::{Sphere, Vec3};
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/// A normalized Ray
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pub struct Ray {
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origin: Vec3,
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direction: Vec3,
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}
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impl Ray {
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pub fn eval(&self, time: f64) -> Vec3 {
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self.origin + self.direction * time
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}
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}
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/// Given a ray and a sphere, returns the first point at which this ray intersects the sphere.
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///
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/// If there is no intersection point, returns None.
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pub fn ray_intersection_time(ray: &Ray, sphere: &Sphere) -> Option<f64> {
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let a =
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ray.direction.x.powi(2) + ray.direction.y.powi(2) + ray.direction.z.powi(2);
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let b = 2.0
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* (ray.direction.x * (ray.origin.x - sphere.center.x)
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+ ray.direction.y * (ray.origin.y - sphere.center.y)
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+ ray.direction.z * (ray.origin.z - sphere.center.z));
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let c = (ray.origin.x - sphere.center.x).powi(2)
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+ (ray.origin.y - sphere.center.y).powi(2)
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+ (ray.origin.z - sphere.center.z).powi(2)
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- sphere.radius.powi(2);
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let discriminant = b * b - 4.0 * a * c;
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match discriminant {
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// Discriminant < 0, means the equation has no solutions.
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d if d < 0.0 => return None,
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// Discriminant == 0
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d if d == 0.0 => {
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return Some(-b / (2.0 * a));
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}
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d if d > 0.0 => {
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let solution_1 = (-b + discriminant.sqrt()) / (2.0 * a);
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let solution_2 = (-b - discriminant.sqrt()) / (2.0 * a);
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return Some(solution_1.min(solution_2));
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}
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_ => unreachable!("Invalid determinant value: {discriminant}"),
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}
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}
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#[cfg(test)]
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mod tests {
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use crate::scene_data::{Sphere, Vec3};
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use super::{ray_intersection_time, Ray};
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#[test]
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fn practice_problem_slide_154() {
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let ray = Ray {
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origin: Vec3::new(0.0, 0.0, 0.0),
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direction: Vec3::new(0.0, 0.0, -1.0),
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};
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let sphere = Sphere {
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center: Vec3::new(0.0, 0.0, -10.0),
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radius: 4.0,
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};
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let t = ray_intersection_time(&ray, &sphere).unwrap();
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assert_eq!(ray.eval(t), Vec3::new(0.0, 0.0, -6.0));
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}
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}
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