make container complicated, heap profiles

.gitignore

@@ -1,2 +1,3 @@
 .DS_Store
 cpuprofile.pprof
+heapprofile.pprof

engine/container.go

@@ -6,11 +6,35 @@ var _ interface {
 } = &Container{}
 
 // Container contains many components, in order.
-type Container []interface{}
+type Container struct {
+	Items []interface{}
+
+	free    map[int]struct{}
+	reverse map[interface{}]int
+}
+
+func MakeContainer(items ...interface{}) *Container {
+	c := &Container{Items: items}
+	c.Prepare(nil)
+	return c
+}
+
+func (c *Container) Prepare(*Game) error {
+	if c.reverse == nil {
+		c.reverse = make(map[interface{}]int, len(c.Items))
+		for i, x := range c.Items {
+			c.reverse[x] = i
+		}
+	}
+	if c.free == nil {
+		c.free = make(map[int]struct{})
+	}
+	return nil
+}
 
 // Scan visits every component in the container.
-func (c Container) Scan(visit func(interface{}) error) error {
+func (c *Container) Scan(visit func(interface{}) error) error {
-	for _, x := range c {
+	for _, x := range c.Items {
 		if err := visit(x); err != nil {
 			return err
 		}
@@ -18,12 +42,55 @@ func (c Container) Scan(visit func(interface{}) error) error {
 	return nil
 }
 
+// Len returns the number of items in the container.
+func (c *Container) Len() int { return len(c.Items) }
+
+// Swap swaps two items in the container.
+func (c *Container) Swap(i, j int) {
+	if i == j {
+		return
+	}
+	ifree := c.Items[i] == nil
+	jfree := c.Items[j] == nil
+	switch {
+	case ifree && jfree:
+		return
+	case ifree:
+		c.Items[i] = c.Items[j]
+		c.reverse[c.Items[i]] = i
+		c.free[j] = struct{}{}
+		delete(c.free, i)
+	case jfree:
+		c.Items[j] = c.Items[i]
+		c.reverse[c.Items[j]] = j
+		c.free[i] = struct{}{}
+		delete(c.free, j)
+	default:
+		c.Items[i], c.Items[j] = c.Items[j], c.Items[i]
+		c.reverse[c.Items[i]] = i
+		c.reverse[c.Items[j]] = j
+	}
+}
+
 func (c Container) String() string { return "Container" }
 
-// Register records component in the slice, if parent is the container.
+// Register records component in the slice, if parent is this container. It
+// writes the component to an arbitrary free index in the slice, or appends if
+// there are none free.
 func (c *Container) Register(component, parent interface{}) error {
-	if parent == c {
+	if parent != c {
-		*c = append(*c, component)
+		return nil
+	}
+	if len(c.free) == 0 {
+		c.reverse[component] = len(c.Items)
+		c.Items = append(c.Items, component)
+		return nil
+	}
+	for i := range c.free {
+		c.reverse[component] = i
+		c.Items[i] = component
+		delete(c.free, i)
+		return nil
 	}
 	return nil
 }
@@ -32,28 +99,25 @@ func (c *Container) Register(component, parent interface{}) error {
 // to nil. If the number of nil items is greater than half the slice, the slice
 // is compacted.
 func (c *Container) Unregister(component interface{}) {
-	free := 0
+	if i, found := c.reverse[component]; found {
-	for i, x := range *c {
+		c.Items[i] = nil
-		switch x {
+		c.free[i] = struct{}{}
-		case component:
+		delete(c.reverse, i)
-			(*c)[i] = nil
-			free++
-		case nil:
-			free++
 	}
-	}
+	if len(c.free) > len(c.Items)/2 {
-	if free > len(*c)/2 {
 		c.compact()
 	}
 }
 
 func (c *Container) compact() {
 	i := 0
-	for _, x := range *c {
+	for _, x := range c.Items {
 		if x != nil {
-			(*c)[i] = x
+			c.Items[i] = x
+			c.reverse[x] = i
 			i++
 		}
 	}
-	*c = (*c)[:i]
+	c.Items = c.Items[:i]
+	c.free = make(map[int]struct{})
 }

game/level1.go

@@ -12,7 +12,7 @@ func Level1() *engine.Scene {
 	return &engine.Scene{
 		ID:     "level_1",
 		Bounds: engine.Bounds(image.Rect(-32, -32, 320+32, 240+32)),
-		Child: &engine.Container{
+		Child: engine.MakeContainer(
 			&engine.Parallax{
 				CameraID: "game_camera",
 				Child: &engine.Billboard{
@@ -310,6 +310,6 @@ func Level1() *engine.Scene {
 					},
 				},
 			},
-		},
+		),
 	}
 }

main.go

@@ -18,6 +18,7 @@ import (
 
 const (
 	enableCPUProfile  = true
+	enableHeapProfile = true
 	enableREPL        = true
 	hardcodedLevel1   = true
 	rewriteLevel1     = false
@@ -64,7 +65,7 @@ func main() {
 			Z: math.Sqrt(3),
 		},
 		Root: &engine.DrawDFS{
-			Child: &engine.Container{
+			Child: engine.MakeContainer(
 				&engine.Fill{
 					ID:    "bg_fill",
 					Color: color.Gray{100},
@@ -78,7 +79,7 @@ func main() {
 				},
 				&engine.DebugToast{ID: "toast", Pos: image.Pt(0, 15)},
 				engine.PerfDisplay{},
-			},
+			),
 		},
 	}
 	if err := g.LoadAndPrepare(game.Assets); err != nil {
@@ -92,4 +93,15 @@ func main() {
 	if err := ebiten.RunGame(g); err != nil {
 		log.Fatalf("Game error: %v", err)
 	}
+
+	if enableHeapProfile && runtime.GOOS != "js" {
+		f, err := os.Create("heapprofile.pprof")
+		if err != nil {
+			log.Fatal("could not create heap profile: ", err)
+		}
+		defer f.Close()
+		if err := pprof.WriteHeapProfile(f); err != nil {
+			log.Fatal("could not write heap profile: ", err)
+		}
+	}
 }