a nicer solution :)

engine/interface.go

@@ -17,13 +17,11 @@ var (
 	ColliderType    = reflect.TypeOf((*Collider)(nil)).Elem()
 	DisablerType    = reflect.TypeOf((*Disabler)(nil)).Elem()
 	DrawerType      = reflect.TypeOf((*Drawer)(nil)).Elem()
-	DrawUpdaterType = reflect.TypeOf((*DrawUpdater)(nil)).Elem()
 	HiderType       = reflect.TypeOf((*Hider)(nil)).Elem()
 	IdentifierType  = reflect.TypeOf((*Identifier)(nil)).Elem()
 	LoaderType      = reflect.TypeOf((*Loader)(nil)).Elem()
 	PrepperType     = reflect.TypeOf((*Prepper)(nil)).Elem()
 	ScannerType     = reflect.TypeOf((*Scanner)(nil)).Elem()
-	ScenerType      = reflect.TypeOf((*Scener)(nil)).Elem()
 	SaverType       = reflect.TypeOf((*Saver)(nil)).Elem()
 	TransformerType = reflect.TypeOf((*Transformer)(nil)).Elem()
 	UpdaterType     = reflect.TypeOf((*Updater)(nil)).Elem()
@@ -35,13 +33,11 @@ var (
 		ColliderType,
 		DisablerType,
 		DrawerType,
-		DrawUpdaterType,
 		HiderType,
 		IdentifierType,
 		LoaderType,
 		PrepperType,
 		ScannerType,
-		ScenerType,
 		SaverType,
 		TransformerType,
 		UpdaterType,
@@ -81,13 +77,6 @@ type Drawer interface {
 	DrawOrder() float64
 }
 
-// DrawUpdater components can be both drawn and updated.
-// Same comments as for Drawer and Updater.
-type DrawUpdater interface {
-	Drawer
-	Updater
-}
-
 // Hider components can be hidden.
 type Hider interface {
 	IsHidden() bool
@@ -121,33 +110,6 @@ type Scanner interface {
 	Scan() []interface{}
 }
 
-// Scener components are a scene (Scene or SceneRef).
-type Scener interface {
-	// Q: Why not make Scene able to load itself?
-	// A: Having separate types makes it easier to reason about what is loading
-	//    what. There is less ambiguity about what "save" means (the contents of
-	//    the scene, or the path to the file?) Additionally, the gob decoder
-	//    decodes over existing fields, which could lead to some fun bugs.
-	//
-	// Q: Why not make Scener a small interface, e.g. 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.
-
-	Bounder
-	Disabler
-	Hider
-	Identifier
-	Scanner
-}
-
 // Saver components can be saved to disk.
 type Saver interface {
 	Save() error

engine/scene.go

@@ -2,29 +2,34 @@ package engine
 
 import (
 	"encoding/gob"
-	"image"
 	"io/fs"
 	"path/filepath"
 )
 
 var (
-	// Ensure Scene satisfies Scener.
-	_ Scener = &Scene{}
+	_ scener = &Scene{}
 
-	// Ensure SceneRef satisfies interfaces.
 	_ interface {
 		Loader
-		Scener
+		Saver
+		scener
 	} = &SceneRef{}
 )
 
+type scener interface {
+	Bounder
+	Disabler
+	Hider
+	Identifier
+	Scanner
+}
+
 func init() {
 	gob.Register(&Scene{})
 	gob.Register(&SceneRef{})
-
 }
 
-// Scene just contains a bunch of components.
+// Scene contains a bunch of components.
 type Scene struct {
 	ID
 	Bounds     // world coordinates
@@ -48,7 +53,18 @@ func (s *Scene) Scan() []interface{} { return s.Components }
 type SceneRef struct {
 	Path string
 
-	scene *Scene // not exported for gob reasons
+	*Scene // not gob encoded
+}
+
+// GobDecode saves the byte slice as Path.
+func (r *SceneRef) GobDecode(b []byte) error {
+	r.Path = string(b)
+	return nil
+}
+
+// GobEncode returns Path as a byte slice.
+func (r *SceneRef) GobEncode() ([]byte, error) {
+	return []byte(r.Path), nil
 }
 
 // Load loads the scene from the file.
@@ -57,39 +73,11 @@ func (r *SceneRef) Load(assets fs.FS) error {
 	if err := LoadGobz(sc, assets, r.Path); err != nil {
 		return err
 	}
-	r.scene = sc
+	r.Scene = sc
 	return nil
 }
 
 // Save saves the scene to a file in the current directory.
-func (r *SceneRef) Save() error { return SaveGobz(r.scene, filepath.Base(r.Path)) }
-
-// The rest of the methods forward to r.scene, as such they will
-// panic if the scene isn't loaded.
-
-// BoundingRect returns the Bounds from the scene.
-func (r SceneRef) BoundingRect() image.Rectangle { return r.scene.BoundingRect() }
-
-// IsDisabled returns the value of IsDisabled from the scene.
-func (r SceneRef) IsDisabled() bool { return r.scene.IsDisabled() }
-
-// Disable calls Disable on the scene.
-func (r SceneRef) Disable() { r.scene.Disable() }
-
-// Enable calls Enable on the scene.
-func (r SceneRef) Enable() { r.scene.Enable() }
-
-// IsHidden returns the value of IsHidden from the scene.
-func (r SceneRef) IsHidden() bool { return r.scene.IsHidden() }
-
-// Hide calls Hide on the scene.
-func (r SceneRef) Hide() { r.scene.Hide() }
-
-// Show calls Show on the scene.
-func (r SceneRef) Show() { r.scene.Show() }
-
-// Ident returns the value of Ident from the scene.
-func (r SceneRef) Ident() string { return r.scene.Ident() }
-
-// Scan returns the components in the scene.
-func (r SceneRef) Scan() []interface{} { return r.scene.Scan() }
+func (r *SceneRef) Save() error {
+	return SaveGobz(r.Scene, filepath.Base(r.Path))
+}

main.go

@@ -14,9 +14,14 @@ import (
 	"github.com/hajimehoshi/ebiten/v2"
 )
 
+const (
+	enableCPUProfile = false
+	rewriteLevel1    = false
+)
+
 func main() {
 	// Change to true to enable cpu profile
-	if false && runtime.GOOS != "js" {
+	if enableCPUProfile && runtime.GOOS != "js" {
 		f, err := os.Create("cpuprofile.pprof")
 		if err != nil {
 			log.Fatal("could not create CPU profile: ", err)
@@ -33,7 +38,7 @@ func main() {
 	ebiten.SetWindowTitle("TODO")
 
 	// Change to true to rewrite level1.gobz
-	if false && runtime.GOOS != "js" {
+	if rewriteLevel1 && runtime.GOOS != "js" {
 		writeLevel1()
 	}