Split Scan and Build

engine/debug.go

@@ -1,6 +1,7 @@
 package engine
 
 import (
+	"compress/gzip"
 	"encoding/gob"
 	"errors"
 	"fmt"
@@ -42,11 +43,10 @@ type GobDumper struct {
 	game *Game
 }
 
-func (d *GobDumper) Scan(g *Game) []interface{} {
-	d.game = g
-	return nil
-}
+// Build simply stores the reference to the Game.
+func (d *GobDumper) Build(g *Game) { d.game = g }
 
+// Update waits for the key combo, then dumps the game state into a gzipped gob.
 func (d *GobDumper) Update() error {
 	for _, key := range d.KeyCombo {
 		if !ebiten.IsKeyPressed(key) {
@@ -56,12 +56,17 @@ func (d *GobDumper) Update() error {
 	if d.game == nil {
 		return errors.New("nil d.game in GobDumper.Update")
 	}
-	f, err := os.Create(time.Now().Format("20060102030405.gob"))
+	f, err := os.Create(time.Now().Format("20060102030405.gob.gz"))
 	if err != nil {
 		return err
 	}
 	defer f.Close()
-	if err := gob.NewEncoder(f).Encode(d.game); err != nil {
+	gz := gzip.NewWriter(f)
+	defer gz.Close()
+	if err := gob.NewEncoder(gz).Encode(d.game); err != nil {
+		return err
+	}
+	if err := gz.Close(); err != nil {
 		return err
 	}
 	return f.Close()

engine/game.go

@@ -16,11 +16,18 @@ type Identifier interface {
 	Ident() string
 }
 
-// Scanner components can be scanned. It is called when the game
+// Builder components can be built. It is called when the game
 // component database is being constructed. It should store the Game reference
-// (if needed later on), and return a slice of all subcomponents.
+// (if needed later on).
+type Builder interface {
+	Build(game *Game)
+}
+
+// Scanner components can be scanned. It is called when the game tree is walked
+// (such as when the game component database is constructed).
+// Scan should return a slice containing all subcomponents.
 type Scanner interface {
-	Scan(game *Game) []interface{}
+	Scan() []interface{}
 }
 
 // Game implements the ebiten methods using a collection of components.
@@ -77,7 +84,8 @@ func (g *Game) UnregisterComponent(c interface{}) {
 // Component returns the component with a given ID, or nil if there is none.
 func (g *Game) Component(id string) interface{} { return g.componentsByID[id] }
 
-// Walk calls v with every component, for as long as visit returns true.
+// Walk calls v with every component reachable via Scan, for as long as visit
+// returns true.
 func (g *Game) Walk(v func(interface{}) bool) {
 	g.walk(g.Scene, v)
 }
@@ -87,7 +95,7 @@ func (g *Game) walk(c interface{}, v func(interface{}) bool) {
 		return
 	}
 	if sc, ok := c.(Scanner); ok {
-		for _, c := range sc.Scan(g) {
+		for _, c := range sc.Scan() {
 			if !v(c) {
 				return
 			}
@@ -100,6 +108,9 @@ func (g *Game) walk(c interface{}, v func(interface{}) bool) {
 func (g *Game) Build() {
 	g.componentsByID = make(map[string]interface{})
 	g.Walk(func(c interface{}) bool {
+		if b, ok := c.(Builder); ok {
+			b.Build(g)
+		}
 		g.RegisterComponent(c)
 		return true
 	})

engine/scene.go

@@ -65,7 +65,7 @@ func (s *Scene) sortByZ() {
 }
 
 // Scan returns all subcomponents.
-func (s *Scene) Scan(g *Game) []interface{} { return s.Components }
+func (s *Scene) Scan() []interface{} { return s.Components }
 
 // Update calls Update on all Updater components.
 func (s *Scene) Update() error {

main.go

@@ -74,7 +74,7 @@ func main() {
 		ScreenHeight: screenHeight,
 		ScreenWidth:  screenWidth,
 		Scene: &engine.Scene{
-			ID: "root_scene",
+			ID: "root",
 			Components: []interface{}{
 				&engine.GobDumper{
 					KeyCombo: []ebiten.Key{ebiten.KeyControl, ebiten.KeyD},