1 files changed, 21 insertions, 3 deletions
diff --git a/hitable.go b/hitable.go
index a44026d..1443110 100644
--- a/hitable.go
+++ b/hitable.go
@@ -1,7 +1,16 @@
 package main
 
+import "math"
+
+type HitRecord struct {
+	time   float64
+	point  Vec3D
+	normal Vec3D
+}
+
 type Hitable interface {
-	Hit(ray Ray) bool
+	Hit(ray Ray) HitRecord
+	Normal(point Vec3D) Vec3D
 }
 
 type Sphere struct {
@@ -9,11 +18,20 @@ type Sphere struct {
 	radius float64
 }
 
-func (sphere Sphere) Hit(ray Ray) bool {
+func (sphere Sphere) Normal(point Vec3D) Vec3D {
+	return (SubVec3D(point, sphere.center)).Unit()
+}
+
+func (sphere Sphere) Hit(ray Ray) 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
-	return discriminant > 0
+	if discriminant < 0 {
+		return HitRecord{}
+	}
+	time := (-b - math.Sqrt(discriminant)) / 2.0 / a
+	point := ray.PointAt(time)
+	return HitRecord{time, point, SubVec3D(point, sphere.Normal(point))}
 }