Parallelize the process.

Makefile

@@ -9,4 +9,4 @@ test:
 	go test ./... --cover
 
 clean:
-	rm -rf main *.jpg *.png
+	rm -rf main *.jpg *.png *.prof

src/accelerator/bvh.go

@@ -66,11 +66,11 @@ type Bvh struct {
 func NewBvh(primitives []Primitive) (bvh *Bvh) {
     bvh = &Bvh{}
     bvh.primitives = primitives
-    bvh.root = NewBvhSub(bvh, primitives, 0)
+    bvh.root = NewBvhSub(bvh, primitives)
     return
 }
 
-func NewBvhSub(bvh *Bvh, primitives []Primitive, axis int) *BvhNode {
+func NewBvhSub(bvh *Bvh, primitives []Primitive) *BvhNode {
     if len(primitives) == 1 {
         node := NewLeafNode(primitives[0].Shape)
         bvh.nodes = append(bvh.nodes, *node)
@@ -84,8 +84,9 @@ func NewBvhSub(bvh *Bvh, primitives []Primitive, axis int) *BvhNode {
         bbox.Merge(b)
         items[i] = SortItem{b.Center(), i}
     }
+    axis := bbox.MaxExtent()
 
-    axisSorter := &AxisSorter{items, axis % 3}
+    axisSorter := &AxisSorter{items, axis}
     sort.Sort(axisSorter)
 
     newPrimitives := make([]Primitive, len(primitives))
@@ -94,8 +95,8 @@ func NewBvhSub(bvh *Bvh, primitives []Primitive, axis int) *BvhNode {
     }
 
     iHalf := len(newPrimitives) / 2
-    leftNode := NewBvhSub(bvh, newPrimitives[:iHalf], (axis + 1) % 3)
-    rightNode := NewBvhSub(bvh, newPrimitives[iHalf:], (axis + 1) % 3)
+    leftNode := NewBvhSub(bvh, newPrimitives[:iHalf])
+    rightNode := NewBvhSub(bvh, newPrimitives[iHalf:])
 
     node := NewForkNode(leftNode, rightNode, bbox)
     bvh.nodes = append(bvh.nodes, *node)

src/core/bounds3d.go

@@ -26,6 +26,19 @@ func (b *Bounds3d) Center() (c Vector3d) {
     return
 }
 
+func (b *Bounds3d) MaxExtent() int {
+    v := b.MaxPos.Subtract(b.MinPos)
+    v = v.Abs()
+    switch {
+    case v.X > v.Y && v.X > v.Z:
+        return 0
+    case v.Y > v.Z:
+        return 1
+    default:
+        return 2
+    }
+}
+
 func (b *Bounds3d) Intersect(ray *Ray, tNear *Float, tFar *Float) bool {
     t0 := 0.0
     t1 := ray.MaxDist

src/core/common.go

@@ -12,6 +12,8 @@ const (
     Infinity = Float(1.0e20)
 )
 
+type Semaphore struct {}
+
 func Sign(x Float) Float {
     if x < 0.0 {
         return -1.0

src/core/vector3d.go

@@ -43,6 +43,13 @@ func (v *Vector3d) Divide(s Float) (ret Vector3d) {
     return
 }
 
+func (v *Vector3d) Abs() (ret Vector3d) {
+    ret.X = math.Abs(v.X)
+    ret.Y = math.Abs(v.Y)
+    ret.Z = math.Abs(v.Z)
+    return
+}
+
 func (v1 *Vector3d) Dot(v2 Vector3d) (ret Float) {
     ret = v1.X * v2.X + v1.Y * v2.Y + v1.Z * v2.Z
     return

src/integrator/path.go

@@ -13,12 +13,21 @@ func (integrator *PathIntegrator) Render(bvh *Bvh, sensor Sensor, sampler Sample
     width := sensor.Film().Width
     height := sensor.Film().Height
     film := sensor.Film()
+    sem := make(chan Semaphore, width)
     for y := 0; y < height; y++ {
         for x := 0; x < width; x++ {
-            ray := sensor.SpawnRay(x, y)
-            L := integrator.Li(bvh, ray, sampler)
-            film.Update(x, y, L)
+            go func(x, y int) {
+                ray := sensor.SpawnRay(x, y)
+                L := integrator.Li(bvh, ray, sampler)
+                film.Update(x, y, L)
+                sem <- Semaphore{}
+            } (x, y)
         }
+
+        for x := 0; x < width; x++ {
+            <-sem
+        }
+
         ProgressBar(y + 1, height)
     }
     fmt.Println()

src/main.go

@@ -20,7 +20,7 @@ const (
 )
 
 func main() {
-    cpuprofile := "mycpu.prof"
+    cpuprofile := "profile.prof"
     f, err := os.Create(cpuprofile)
     if err != nil {
        log.Fatal(err)