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package main
import "math"
type HitRecord struct {
time float64
point Vec3D
normal Vec3D
}
type Hitable interface {
Hit(ray Ray, t_min float64, t_max float64) HitRecord
Normal(point Vec3D, ray Ray) Vec3D
}
type HitableList []Hitable
func (hitable_list HitableList) Hit(ray Ray, t_min float64, t_max float64) HitRecord {
closest_hit := HitRecord{T_MAX, Vec3D{}, Vec3D{}}
for _, hitable := range hitable_list {
hit := hitable.Hit(ray, t_min, closest_hit.time)
if hit.time > 0 {
closest_hit = hit
}
}
if closest_hit.time < T_MAX {
return closest_hit
} else {
return HitRecord{}
}
}
type Sphere struct {
center Vec3D
radius float64
}
func (sphere Sphere) Normal(point Vec3D, ray Ray) Vec3D {
out_normal := SubVec3D(point, sphere.center).Unit()
if DotProduct(ray.direction, out_normal) < 0.0 {
return out_normal
} else {
return out_normal.Invert()
}
}
func (sphere Sphere) Hit(ray Ray, t_min float64, t_max 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 t_min < time && time < t_max {
point := ray.PointAt(time)
return HitRecord{time, point, sphere.Normal(point, ray)}
}
time = (-b + root) / (2.0 * a)
if t_min < time && time < t_max {
point := ray.PointAt(time)
return HitRecord{time, point, sphere.Normal(point, ray)}
}
}
return HitRecord{}
}
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