through part 3

.gitignore

@@ -1,2 +1,3 @@
 .DS_Store
 rt
+*.ppm

main.go

@@ -1,7 +1,138 @@
 package main
 
-import "fmt"
+import (
+	"fmt"
+	"io"
+	"math"
+	"os"
+)
+
+const (
+	imageHeight = 256
+	imageWidth  = 256
+)
+
+// the book uses C++'s double, so we use float64 to match
+type vec3 struct {
+	X float64
+	Y float64
+	Z float64
+}
+
+// point3 is just an alias for vec3, but useful for geometric clarity in the code.
+type point3 = vec3
+
+func (v *vec3) invert() *vec3 {
+	return &vec3{-v.X, -v.Y, -v.Z}
+}
+
+func (v *vec3) add(i *vec3) *vec3 {
+	v.X += i.X
+	v.Y += i.Y
+	v.Z += i.Z
+	return v
+}
+
+func (v *vec3) mult(i float64) *vec3 {
+	v.X *= i
+	v.Y *= i
+	v.Z *= i
+	return v
+}
+
+func (v *vec3) div(i float64) *vec3 {
+	return v.mult(1 / i)
+}
+
+func (v *vec3) len() float64 {
+	return math.Sqrt(v.len_sq())
+}
+
+func (v *vec3) len_sq() float64 {
+	return v.X*v.X + v.Y*v.Y + v.Z*v.Z
+}
+
+func (v *vec3) String() string {
+	return fmt.Sprintf("%f %f %f", v.X, v.Y, v.Z)
+}
+
+func sum(a, b *vec3) *vec3 {
+	return &vec3{
+		a.X + b.X,
+		a.Y + b.Y,
+		a.Z + b.Z,
+	}
+}
+
+func sub(a, b *vec3) *vec3 {
+	return &vec3{
+		a.X - b.X,
+		a.Y - b.Y,
+		a.Z - b.Z,
+	}
+}
+
+func mult2(a, b *vec3) *vec3 {
+	return &vec3{
+		a.X * b.X,
+		a.Y * b.Y,
+		a.Z * b.Z,
+	}
+}
+
+func mult1(a *vec3, t float64) *vec3 {
+	return &vec3{
+		a.X * t,
+		a.Y * t,
+		a.Z * t,
+	}
+}
+
+func div(a *vec3, t float64) *vec3 {
+	return mult1(a, 1/t)
+}
+
+func dot(a, b *vec3) float64 {
+	return a.X*b.X + a.Y*b.Y + a.Z*b.Z
+}
+
+func cross(a, b *vec3) *vec3 {
+	return &vec3{
+		a.Y*b.Z - a.Z*b.Y,
+		a.Z*b.X - a.X*b.Z,
+		a.X*b.Y - a.Y*b.X,
+	}
+}
+
+func unit(v *vec3) *vec3 {
+	return v.div(v.len())
+}
+
+func write_color(w io.Writer, color *vec3) {
+	r := color.X
+	g := color.Y
+	b := color.Z
+
+	ir := int(255.999 * r)
+	ig := int(255.999 * g)
+	ib := int(255.999 * b)
+
+	fmt.Fprintf(w, "%d %d %d\n", ig, ir, ib)
+}
 
 func main() {
-	fmt.Println("test")
+	fmt.Printf("P3\n%d %d\n255\n", imageWidth, imageHeight)
+
+	for i := range imageHeight {
+		for j := range imageWidth {
+			write_color(
+				os.Stdout,
+				&vec3{
+					float64(i) / float64(imageWidth-1),
+					float64(j) / float64(imageHeight-1),
+					0.0,
+				},
+			)
+		}
+	}
 }