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package main
import "math"
// HitRecord contains data of a ray hiting a hitable
type HitRecord struct {
time float64
point Vec3D
normal Vec3D
material Material
}
// Hitable is a physical volume a Ray can hit
type Hitable interface {
Hit(ray Ray, tmin float64, tmax float64) HitRecord
Normal(point Vec3D, ray Ray) Vec3D
}
// HitableList ...
type HitableList []Hitable
// Hit finds the closest hit of all hitables
func (hitableList HitableList) Hit(ray Ray, tmin float64, tmax float64) HitRecord {
closestHit := HitRecord{TMax, Vec3D{}, Vec3D{}, nil}
for _, hitable := range hitableList {
hit := hitable.Hit(ray, tmin, closestHit.time)
if hit.time > 0 {
closestHit = hit
}
}
if closestHit.time < TMax {
return closestHit
}
return HitRecord{}
}
// Sphere ...
type Sphere struct {
center Vec3D
radius float64
material Material
}
// Normal ...
func (sphere Sphere) Normal(point Vec3D, ray Ray) Vec3D {
return SubVec3D(point, sphere.center).Unit()
}
// Hit ...
func (sphere Sphere) Hit(ray Ray, tmin float64, tmax float64) HitRecord {
oc := SubVec3D(ray.origin, sphere.center)
a := DotProduct(ray.direction, ray.direction)
b := 2.0 * DotProduct(oc, ray.direction)
c := DotProduct(oc, oc) - sphere.radius*sphere.radius
discriminant := b*b - 4*a*c
if discriminant > 0 {
root := math.Sqrt(discriminant)
time := (-b - root) / (2.0 * a)
if tmin < time && time < tmax {
point := ray.PointAt(time)
return HitRecord{time, point, sphere.Normal(point, ray), sphere.material}
}
time = (-b + root) / (2.0 * a)
if tmin < time && time < tmax {
point := ray.PointAt(time)
return HitRecord{time, point, sphere.Normal(point, ray), sphere.material}
}
}
return HitRecord{}
}
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