77 lines
2.1 KiB
Rust
77 lines
2.1 KiB
Rust
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use anyhow::Result;
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use nalgebra::Vector3;
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use ordered_float::NotNan;
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use crate::{ray::Ray, utils::min_f64};
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use super::data::{IntersectionContext, ObjectKind};
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#[derive(Debug)]
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pub struct Sphere {
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pub center: Vector3<f64>,
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pub radius: f64,
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}
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impl ObjectKind for Sphere {
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/// Given a sphere, returns the first time at which this ray intersects the
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/// sphere.
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///
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/// If there is no intersection point, returns None.
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fn intersects_ray_at(
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&self,
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ray: &Ray,
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) -> Result<Option<IntersectionContext>> {
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let a = ray.direction.x.powi(2)
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+ ray.direction.y.powi(2)
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+ ray.direction.z.powi(2);
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let b = 2.0
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* (ray.direction.x * (ray.origin.x - self.center.x)
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+ ray.direction.y * (ray.origin.y - self.center.y)
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+ ray.direction.z * (ray.origin.z - self.center.z));
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let c = (ray.origin.x - self.center.x).powi(2)
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+ (ray.origin.y - self.center.y).powi(2)
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+ (ray.origin.z - self.center.z).powi(2)
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- self.radius.powi(2);
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let discriminant = b * b - 4.0 * a * c;
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let time = match discriminant {
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// Discriminant < 0, means the equation has no solutions.
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d if d < 0.0 => None,
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// Discriminant == 0
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d if d == 0.0 => Some(-b / (2.0 * a)),
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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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let solutions = [solution_1, solution_2]
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.into_iter()
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// Remove any t < 0, since that means it's behind the viewer and we
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// can't see it.
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.filter(|t| *t >= 0.0);
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// Return the minimum solution
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min_f64(solutions)
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}
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// Probably hit some NaN or Infinity value due to faulty inputs...
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_ => unreachable!("Invalid determinant value: {discriminant}"),
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};
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let time = match time.and_then(|t| NotNan::new(t).ok()) {
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Some(v) => v,
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None => return Ok(None),
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};
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let point = ray.eval(*time);
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let normal = (point - self.center).normalize();
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Ok(Some(IntersectionContext {
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time,
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point,
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normal,
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}))
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}
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}
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