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//! Implements sphere
//!
//! Spheres are relatively easy to calculate intersections between
use crate::Float;
use crate::core::{Ray, Vector3f, Hittable, Intersection};
pub struct Sphere {
radius: Float,
center: Vector3f,
}
impl Sphere {
pub fn new(radius: Float, center: Vector3f) -> Sphere {
Sphere {
radius,
center,
}
}
fn norm_at(&self, point: &Vector3f) -> Vector3f {
let mut v = *point - self.center;
v /= self.radius;
v
}
}
impl Hittable for Sphere {
// Implementation from ray tracing in a weekend
fn intersect(&self, ray: &Ray) -> Option<Intersection> {
let oc = ray.origin - self.center;
let a = ray.direction.len_squared();
let half_b = oc.dot(&ray.direction);
let c = oc.len_squared() - self.radius * self.radius;
let disc = half_b*half_b - a*c;
if disc < 0.0 {
None
} else {
let distance = (-half_b - disc.sqrt()) / a;
if distance < 0.0 {
return None
}
let w = ray.at(distance);
Some(Intersection {
n: self.norm_at(&w),
p: w,
t: distance,
})
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn sphere_intersect() {
let sph = Sphere::new(2.0, Vector3f::new_xyz(2.0, 3.0, 4.0));
let ray = Ray {
origin: Vector3f::new_xyz(1.0, 0.0, 0.0),
direction: Vector3f::new_xyz(0.0, 1.0, 1.5).norm(),
};
let dist = sph.intersect(&ray).unwrap();
assert!((dist.t - 3.28).abs() < 0.01);
}
}
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