1 files changed, 40 insertions, 10 deletions

diff --git a/hitable.go b/hitable.go
index ed18a5d..bc9f9bc 100644
--- a/hitable.go
+++ b/hitable.go
@@ -9,8 +9,25 @@ type HitRecord struct {
 }
 
 type Hitable interface {
-	Hit(ray Ray) HitRecord
-	Normal(point Vec3D) Vec3D
+	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 {
@@ -18,20 +35,33 @@ type Sphere struct {
 	radius float64
 }
 
-func (sphere Sphere) Normal(point Vec3D) Vec3D {
-	return SubVec3D(point, sphere.center).Unit()
+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) HitRecord {
+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 {
-		return HitRecord{}
+	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)}
+		}
 	}
-	time := (-b - math.Sqrt(discriminant)) / (2.0 * a)
-	point := ray.PointAt(time)
-	return HitRecord{time, point, sphere.Normal(point)}
+	return HitRecord{}
 }