From 13be7ded788fe88d5ac8d6759273516652bf1a80 Mon Sep 17 00:00:00 2001
From: Martin Lehoux <martin@lehoux.net>
Date: Sat, 4 Apr 2020 19:41:57 -0700
Subject: feat - Add Lambertian material

---
 color.go    |  6 ++----
 hitable.go  | 18 ++++++++++--------
 main.go     |  7 +++++--
 material.go | 16 ++++++++++++++++
 4 files changed, 33 insertions(+), 14 deletions(-)
 create mode 100644 material.go

diff --git a/color.go b/color.go
index 857bc41..bb7318a 100644
--- a/color.go
+++ b/color.go
@@ -32,10 +32,8 @@ func RayColor(ray Ray, hitable_list HitableList, depth int) Color {
 	}
 	hit := hitable_list.Hit(ray, T_MIN, T_MAX)
 	if hit.time > 0.0 {
-		// TODO: Use the correct distribution
-		direction := AddVec3D(hit.normal, RandomInUnitSphere())
-		scattered := Ray{hit.point, direction}
-		return AttenuateColor(Color{0.5, 0.5, 0.5}, RayColor(scattered, hitable_list, depth+1))
+		scattered, attenuation := hit.material.Scatter(ray, hit)
+		return AttenuateColor(attenuation, RayColor(scattered, hitable_list, depth+1))
 	}
 	param := 0.5 * (ray.direction.Unit().y + 1)
 	return LinearBlend(Color{0.5, 0.7, 1.0}, Color{1.0, 1.0, 1.0}, param)
diff --git a/hitable.go b/hitable.go
index bc9f9bc..ef5822f 100644
--- a/hitable.go
+++ b/hitable.go
@@ -3,9 +3,10 @@ package main
 import "math"
 
 type HitRecord struct {
-	time   float64
-	point  Vec3D
-	normal Vec3D
+	time     float64
+	point    Vec3D
+	normal   Vec3D
+	material Material
 }
 
 type Hitable interface {
@@ -16,7 +17,7 @@ type Hitable interface {
 type HitableList []Hitable
 
 func (hitable_list HitableList) Hit(ray Ray, t_min float64, t_max float64) HitRecord {
-	closest_hit := HitRecord{T_MAX, Vec3D{}, Vec3D{}}
+	closest_hit := HitRecord{T_MAX, Vec3D{}, Vec3D{}, nil}
 	for _, hitable := range hitable_list {
 		hit := hitable.Hit(ray, t_min, closest_hit.time)
 		if hit.time > 0 {
@@ -31,8 +32,9 @@ func (hitable_list HitableList) Hit(ray Ray, t_min float64, t_max float64) HitRe
 }
 
 type Sphere struct {
-	center Vec3D
-	radius float64
+	center   Vec3D
+	radius   float64
+	material Material
 }
 
 func (sphere Sphere) Normal(point Vec3D, ray Ray) Vec3D {
@@ -55,12 +57,12 @@ func (sphere Sphere) Hit(ray Ray, t_min float64, t_max float64) HitRecord {
 		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{time, point, sphere.Normal(point, ray), sphere.material}
 		}
 		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{time, point, sphere.Normal(point, ray), sphere.material}
 		}
 	}
 	return HitRecord{}
diff --git a/main.go b/main.go
index 291e60f..b8f6335 100644
--- a/main.go
+++ b/main.go
@@ -20,8 +20,11 @@ func main() {
 	VERTICAL := Vec3D{0.0, 2.0, 0.0}
 	CAMERA := Camera{LOWER_LEFT_CORNER, ORIGIN, HORIZONTAL, VERTICAL}
 
-	SPHERE := Sphere{Vec3D{0.0, 0.0, -1.0}, 0.5}
-	EARTH := Sphere{Vec3D{0.0, -100.5, -1.0}, 100.0}
+	MAT_RED := Lambertian{Color{0.7, 0.3, 0.3}}
+	MAT_GREEN := Lambertian{Color{0.8, 0.8, 0.0}}
+
+	SPHERE := Sphere{Vec3D{0.0, 0.0, -1.0}, 0.5, MAT_RED}
+	EARTH := Sphere{Vec3D{0.0, -100.5, -1.0}, 100.0, MAT_GREEN}
 
 	WORLD := HitableList{EARTH, SPHERE}
 	frame := Frame{}
diff --git a/material.go b/material.go
new file mode 100644
index 0000000..db1e4d6
--- /dev/null
+++ b/material.go
@@ -0,0 +1,16 @@
+package main
+
+type Material interface {
+	Scatter(ray Ray, hit HitRecord) (Ray, Color)
+}
+
+type Lambertian struct {
+	albedo Color
+}
+
+func (lambertian Lambertian) Scatter(ray Ray, hit HitRecord) (Ray, Color) {
+	// TODO: Use the correct distribution
+	direction := AddVec3D(hit.normal, RandomInUnitSphere())
+	scattered := Ray{hit.point, direction}
+	return scattered, lambertian.albedo
+}
-- 
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