big Scener won

engine/asset.go

@@ -24,6 +24,12 @@ var (
 	_ Scener = &SceneRef{}
 )
 
+func init() {
+	gob.Register(AnimRef{})
+	gob.Register(ImageRef{})
+	gob.Register(SceneRef{})
+}
+
 // AnimRef manages an Anim using a premade AnimDef from the cache.
 type AnimRef struct {
 	Key string
@@ -80,6 +86,13 @@ func (r *ImageRef) Image() *ebiten.Image {
 
 // SceneRef loads a gzipped, gob-encoded Scene from the asset FS.
 // After Load, Scene is usable.
+// This is mostly useful for scenes that refer to other scenes, e.g.
+//
+//    var sc = &Scene{
+//	    Components: []interface{}{
+//			SceneRef{Path: "assets/foo.gob.gz"}
+//		},
+//    }
 type SceneRef struct {
 	Path string
 
@@ -112,3 +125,26 @@ func (r *SceneRef) Load() error {
 
 // Scene returns the loaded scene, or nil if not yet loaded.
 func (r SceneRef) Scene() *Scene { return r.scene }
+
+// The rest of the methods forward to r.scene, as such they will
+// panic if the scene isn't loaded.
+
+// Draw draws the scene.
+func (r SceneRef) Draw(screen *ebiten.Image, opts ebiten.DrawImageOptions) {
+	r.scene.Draw(screen, opts)
+}
+
+// DrawOrder returns the value of DrawOrder from the scene.
+func (r SceneRef) DrawOrder() float64 { return r.scene.DrawOrder() }
+
+// Ident returns the value of Ident from the scene.
+func (r SceneRef) Ident() string { return r.scene.Ident() }
+
+// Prepare prepares the scene.
+func (r SceneRef) Prepare(g *Game) { r.scene.Prepare(g) }
+
+// Scan returns the components in the scene.
+func (r SceneRef) Scan() []interface{} { return r.scene.Scan() }
+
+// Update updates the scene.
+func (r SceneRef) Update() error { return r.scene.Update() }

engine/game.go

@@ -24,11 +24,6 @@ func (g *Game) Draw(screen *ebiten.Image) {
 	g.Scene().Draw(screen, ebiten.DrawImageOptions{})
 }
 
-// Update updates the current scene.
-func (g *Game) Update() error {
-	return g.Scene().Update()
-}
-
 // Layout returns the configured screen width/height.
 func (g *Game) Layout(outsideWidth, outsideHeight int) (w, h int) {
 	return g.ScreenWidth, g.ScreenHeight
@@ -88,7 +83,8 @@ func Walk(c interface{}, v func(interface{}) error) error {
 
 // Prepare builds the component database (using Walk) and then calls
 // Prepare on every Preparer. You must call Prepare before any calls
-// to Component.
+// to Component. You may call Prepare again (e.g. as an alternative to
+// fastidiously calling RegisterComponent/UnregisterComponent).
 func (g *Game) Prepare() {
 	g.componentsByID = make(map[string]interface{})
 	Walk(g, func(c interface{}) error {

engine/interface.go

@@ -57,7 +57,24 @@ type Scanner interface {
 
 // Scener components are a scene (Scene or SceneRef).
 type Scener interface {
+	// Q: Why not make Scener a small interface with just Scene() ?
+	// A: Everything in the engine would then need to type switch for Scener or SceneRef, i.e.
+	// switch x := i.(type) {
+	// case Drawer:
+	//     i.Draw(screen, opts)
+	// case Scener:
+	//     i.Scene().Draw(screen, opts)
+	// }
+	// It seems cleaner to let the engine assert only for the interface it needs at that moment.
+
+	Drawer
+	DrawOrderer
+	Identifier
 	Loader
+	Prepper
+	Scanner
+	Updater
+
 	Scene() *Scene
 }
 

engine/scene.go

@@ -10,16 +10,7 @@ import (
 )
 
 // Ensure Scene satisfies Scener.
-var (
+var _ Scener = &Scene{}
-	_ Drawer      = &Scene{}
-	_ DrawOrderer = &Scene{}
-	_ Identifier  = &Scene{}
-	_ Loader      = &Scene{}
-	_ Scanner     = &Scene{}
-	_ Scener      = &Scene{}
-	_ Prepper     = &Scene{}
-	_ Updater     = &Scene{}
-)
 
 func init() {
 	gob.Register(Scene{})
@@ -48,7 +39,7 @@ func (s *Scene) Draw(screen *ebiten.Image, opts ebiten.DrawImageOptions) {
 	}
 }
 
-// Load loads any components that need loading.
+// Load loads any subcomponents that need loading.
 func (s *Scene) Load() error {
 	for _, i := range s.Components {
 		l, ok := i.(Loader)

main.go

@@ -116,6 +116,9 @@ func main() {
 			},
 		},
 	}
+	if err := game.Load(); err != nil {
+		log.Fatalf("Loading error: %v", err)
+	}
 	game.Prepare()
 
 	if err := ebiten.RunGame(game); err != nil {