Chapter 5 done :D

main.go

@@ -94,8 +94,8 @@ func Cross(v1 Vec3, v2 Vec3) Vec3 {
 }
 
 func Unit_vector(v Vec3) Vec3 {
-	v.Div(v.Length())
-     return v
+	new_v := v.Div(v.Length())
+    return new_v
 }
 
 // ============== COLOUR CLASS ==============
@@ -141,11 +141,31 @@ func (r *Ray) At(t float32) Vec3 {
 }
 
 func Ray_color(r *Ray) Vec3 {
+	if (hit_sphere(NewPoint3(0,0,-1), 0.5, r)) {
+		return NewColor(1, 0, 0)
+	}
+	
 	unit_direction := Unit_vector(r.Direction())
-	var a float32 = 0.5*unit_direction.Y() + 0.5
+	a := (unit_direction.Y() + 1.0)*0.5
+
 	return NewColor(1.0,1.0,1.0).Mult(float32(1.0-a)).Add(NewColor(0.5,0.7,1.0).Mult(a))
 }
 
+// =============== SPHERE ===================
+
+func hit_sphere(center Vec3, radius float32, r *Ray) bool {
+	oc := r.Origin().Sub(center)
+	a := Dot(r.Direction(), r.Direction())
+	b := Dot(oc, r.Direction()) * 2.0
+	c := Dot(oc, oc) - radius*radius
+	discriminant := b*b - 4*a*c
+	if discriminant >= 0 {
+		return true
+	} else {
+		return false
+	}
+}
+
 // =============== MAIN =====================
 func main() {
 
@@ -161,7 +181,7 @@ func main() {
 	 // Camera
 	 var focal_length float32 = 1.0
 	 var viewport_height float32 = 2.0
-	 var viewport_width float32 = viewport_height * float32(image_width/image_height)
+	 var viewport_width float32 = viewport_height * float32(image_width)/float32(image_height)
 	 camera_center := NewVec3(0,0,0)
 
 	 // Calculate the vectors across the horizontal and down the vertical viewport edges