bunch of changes

engine/billboard.go

@@ -52,7 +52,7 @@ func (b *Billboard) Prepare(g *Game) error {
 }
 
 // Scan returns a slice containing Src.
-func (b *Billboard) Scan() []interface{} { return []interface{}{&b.Src} }
+func (b *Billboard) Scan() Components { return Components{&b.Src} }
 
 func (b *Billboard) String() string {
 	return fmt.Sprintf("Billboard@%v", b.Pos)

engine/camera.go

@@ -86,7 +86,7 @@ func (c *Camera) Prepare(game *Game) error {
 }
 
 // Scan returns s.Child.
-func (c *Camera) Scan() []interface{} { return []interface{}{c.Child} }
+func (c *Camera) Scan() Components { return Components{c.Child} }
 
 // Transform returns the camera transform.
 func (c *Camera) Transform() (opts ebiten.DrawImageOptions) {

engine/drawdag.go

@@ -14,6 +14,7 @@ var _ interface {
 	DrawManager
 	Hider
 	Prepper
+	Registrar
 	Scanner
 	Updater
 } = &DrawDAG{}
@@ -24,7 +25,7 @@ var _ interface {
 // the number of tests between components.
 type DrawDAG struct {
 	ChunkSize int
-	Components []interface{}
+	Components
 	Hides
 
 	*dag
@@ -110,15 +111,11 @@ func (d *DrawDAG) Prepare(game *Game) error {
 	d.game = game
 
 	// Because Game.LoadAndPrepare calls Prepare in a post-order walk, all the
-	// descendants should be prepared, meaning BoundingBox (hence Add) is likely
-	// to be a safe call.
-	d.addRecursive(d)
-	return nil
+	// descendants should be prepared, meaning BoundingBox (hence Register) is
+	// likely to be a safe call.
+	return d.Register(d, nil)
 }
 
-// Scan returns d.Components.
-func (d *DrawDAG) Scan() []interface{} { return d.Components }
-
 // Update checks for any changes to descendants, and updates its internal
 // data structures accordingly.
 func (d *DrawDAG) Update() error {
@@ -130,20 +127,38 @@ func (d *DrawDAG) Update() error {
 	for db, bb := range d.boxCache {
 		nbb := db.BoundingBox()
 		if bb != nbb {
-			d.Remove(db)
+			d.Unregister(db)
 			readd = append(readd, db)
 		}
 	}
 	for _, db := range readd {
-		d.Add(db)
+		d.Register(db, nil)
 	}
 	return nil
 }
 
-// Add adds a Drawer and any needed edges to the DAG and chunk map. If x is
-// intended to be a direct subcomponent of d, then the caller must append to
-// d.Components as well.
-func (d *DrawDAG) Add(x DrawBoxer) {
+// Register recursively registers compponent and all descendants that are
+// DrawBoxers into internal data structures (the DAG, etc) unless they are
+// descendants of a different DrawManager.
+func (d *DrawDAG) Register(component, _ interface{}) error {
+	if db, ok := component.(DrawBoxer); ok {
+		d.registerOne(db)
+	}
+	if _, ok := component.(DrawManager); ok && component != d {
+		return nil
+	}
+	if sc, ok := component.(Scanner); ok {
+		for _, x := range sc.Scan() {
+			if err := d.Register(x, nil); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// registerOne adds component and any needed edges to the DAG and chunk map.
+func (d *DrawDAG) registerOne(x DrawBoxer) {
 	// Ensure vertex is present
 	d.dag.addVertex(x)
 
@@ -196,24 +211,22 @@ func (d *DrawDAG) Add(x DrawBoxer) {
 	}
 }
 
-// addRecursive adds x and all descendants that are DrawBoxers unless they are
-// descendants of a different DrawManager.
-func (d *DrawDAG) addRecursive(x interface{}) {
-	if db, ok := x.(DrawBoxer); ok {
-		d.Add(db)
+// Unregister unregisters the component and all subcomponents.
+func (d *DrawDAG) Unregister(component interface{}) {
+	if db, ok := component.(DrawBoxer); ok {
+		d.unregisterOne(db)
 	}
-	if _, ok := x.(DrawManager); ok && x != d {
+	if _, ok := component.(DrawManager); ok && component != d {
 		return
 	}
-	if sc, ok := x.(Scanner); ok {
+	if sc, ok := component.(Scanner); ok {
 		for _, x := range sc.Scan() {
-			d.addRecursive(x)
+			d.Unregister(x)
 		}
 	}
 }
 
-// Remove removes a Drawer and all associated edges and metadata.
-func (d *DrawDAG) Remove(x DrawBoxer) {
+func (d *DrawDAG) unregisterOne(x DrawBoxer) {
 	// Remove from chunk map
 	revr := d.chunksRev[x]
 	for j := revr.Min.Y; j <= revr.Max.Y; j++ {

engine/drawdfs.go

@@ -13,7 +13,7 @@ var _ interface {
 // through the game tree, without any extra sorting based on Z values or
 // consideration for DrawOrderer).
 type DrawDFS struct {
-	Components []interface{}
+	Components
 	Hides
 }
 
@@ -53,5 +53,3 @@ func (d *DrawDFS) draw(component interface{}, screen *ebiten.Image, opts ebiten.
 		}
 	}
 }
-
-func (d *DrawDFS) Scan() []interface{} { return d.Components }

engine/game.go

@@ -20,6 +20,7 @@ var _ interface {
 	Hider
 	Identifier
 	Updater
+	Registrar
 	Scanner
 } = &Game{}
 
@@ -154,7 +155,7 @@ func (g *Game) Query(ancestor interface{}, behaviour reflect.Type) map[interface
 }
 
 // Scan returns g.Root.
-func (g *Game) Scan() []interface{} { return []interface{}{g.Root} }
+func (g *Game) Scan() Components { return Components{g.Root} }
 
 // PreorderWalk calls visit with every component and its parent, reachable from
 // the  given component via Scan, for as long as visit returns nil. The parent
@@ -225,7 +226,7 @@ func (g *Game) LoadAndPrepare(assets fs.FS) error {
 	g.byID = make(map[string]Identifier)
 	g.byAB = make(map[abKey]map[interface{}]struct{})
 	g.par = make(map[interface{}]interface{})
-	if err := PreorderWalk(g, g.register); err != nil {
+	if err := PreorderWalk(g, g.registerOne); err != nil {
 		return err
 	}
 	g.dbmu.Unlock()
@@ -261,10 +262,10 @@ func (g *Game) Register(component, parent interface{}) error {
 	g.dbmu.Lock()
 	defer g.dbmu.Unlock()
 	// preorderWalk goes in the right order for registering.
-	return preorderWalk(component, parent, g.register)
+	return preorderWalk(component, parent, g.registerOne)
 }
 
-func (g *Game) register(component, parent interface{}) error {
+func (g *Game) registerOne(component, parent interface{}) error {
 	// register in g.byID if needed
 	if i, ok := component.(Identifier); ok {
 		if id := i.Ident(); id != "" {
@@ -307,11 +308,11 @@ func (g *Game) Unregister(component interface{}) {
 	}
 	g.dbmu.Lock()
 	// postorderWalk goes in the right order for unregistering.
-	postorderWalk(component, nil, g.unregister)
+	postorderWalk(component, nil, g.unregisterOne)
 	g.dbmu.Unlock()
 }
 
-func (g *Game) unregister(component, _ interface{}) error {
+func (g *Game) unregisterOne(component, _ interface{}) error {
 	// unregister from g.byAB, using g.par to trace the path
 	ct := reflect.TypeOf(component)
 	for _, b := range Behaviours {

engine/interface.go

@@ -25,6 +25,7 @@ var (
 	IdentifierType     = reflect.TypeOf((*Identifier)(nil)).Elem()
 	LoaderType         = reflect.TypeOf((*Loader)(nil)).Elem()
 	PrepperType        = reflect.TypeOf((*Prepper)(nil)).Elem()
+	RegistrarType      = reflect.TypeOf((*Registrar)(nil)).Elem()
 	SaverType          = reflect.TypeOf((*Saver)(nil)).Elem()
 	ScannerType        = reflect.TypeOf((*Scanner)(nil)).Elem()
 	TransformerType    = reflect.TypeOf((*Transformer)(nil)).Elem()
@@ -44,6 +45,7 @@ var (
 		IdentifierType,
 		LoaderType,
 		PrepperType,
+		RegistrarType,
 		SaverType,
 		ScannerType,
 		TransformerType,
@@ -128,6 +130,14 @@ type Prepper interface {
 	Prepare(game *Game) error
 }
 
+// Registrar components can register and unregister other components (usually
+// into internal data structures). Registrars are expected to automatically
+// register/unregister subcomponents of components (usually recursively).
+type Registrar interface {
+	Register(component, parent interface{}) error
+	Unregister(component interface{})
+}
+
 // Saver components can be saved to disk.
 type Saver interface {
 	Save() error
@@ -137,7 +147,7 @@ type Saver interface {
 // (such as when the game component database is constructed).
 // Scan should return a slice containing all immediate subcomponents.
 type Scanner interface {
-	Scan() []interface{}
+	Scan() Components
 }
 
 // Transformer components can provide draw options to apply to themselves and

engine/misc.go

@@ -39,3 +39,9 @@ func (h *Hides) Hide() { *h = true }
 
 // Show sets h to false.
 func (h *Hides) Show() { *h = false }
+
+// Components implements Scan directly (as a slice of interface{}).
+type Components []interface{}
+
+// Scan returns c.
+func (c Components) Scan() Components { return c }

engine/parallax.go

@@ -39,7 +39,7 @@ func (p *Parallax) Prepare(game *Game) error {
 }
 
 // Scan returns the child component.
-func (p *Parallax) Scan() []interface{} { return []interface{}{p.Child} }
+func (p *Parallax) Scan() Components { return Components{p.Child} }
 
 // Transform returns a GeoM translation of Factor * camera.Centre.
 func (p *Parallax) Transform() (opts ebiten.DrawImageOptions) {

engine/prisms.go

@@ -16,6 +16,7 @@ var (
 		Disabler
 		Hider
 		Prepper
+		Scanner
 		Transformer
 	} = &PrismMap{}
 
@@ -112,8 +113,8 @@ func (m *PrismMap) Prepare(g *Game) error {
 }
 
 // Scan returns the Sheet and all the Prisms.
-func (m *PrismMap) Scan() []interface{} {
-	c := make([]interface{}, 1, len(m.Map)+1)
+func (m *PrismMap) Scan() Components {
+	c := make(Components, 1, len(m.Map)+1)
 	c[0] = &m.Sheet
 	for _, prism := range m.Map {
 		c = append(c, prism)

engine/scene.go

@@ -29,18 +29,16 @@ func init() {
 	gob.Register(&SceneRef{})
 }
 
-// Scene contains a bunch of components.
+// Scene gives an identity, bounds, and other properties to a collection of
+// components.
 type Scene struct {
 	ID
 	Bounds // world coordinates
-	Components []interface{}
+	Components
 	Disables
 	Hides
 }
 
-// Scan returns all immediate subcomponents (including the camera, if not nil).
-func (s *Scene) Scan() []interface{} { return s.Components }
-
 // 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.

engine/sheet.go

@@ -47,7 +47,7 @@ func (s *Sheet) Prepare(*Game) error {
 }
 
 // Scan returns the Src.
-func (s *Sheet) Scan() []interface{} { return []interface{}{&s.Src} }
+func (s *Sheet) Scan() Components { return Components{&s.Src} }
 
 // SubImage returns an *ebiten.Image corresponding to the given cell index.
 func (s *Sheet) SubImage(i int) *ebiten.Image {

engine/sprite.go

@@ -41,8 +41,8 @@ func (s *Sprite) Draw(screen *ebiten.Image, opts *ebiten.DrawImageOptions) {
 }
 
 // Scan returns the Actor and the Sheet.
-func (s *Sprite) Scan() []interface{} {
-	return []interface{}{
+func (s *Sprite) Scan() Components {
+	return Components{
 		&s.Actor,
 		&s.Sheet,
 	}

engine/tiles.go

@@ -100,8 +100,8 @@ func (t *Tilemap) Load(fs.FS) error {
 }
 
 // Scan returns a slice containing Src and all non-nil tiles.
-func (t *Tilemap) Scan() []interface{} {
-	c := make([]interface{}, 1, len(t.Map)+1)
+func (t *Tilemap) Scan() Components {
+	c := make(Components, 1, len(t.Map)+1)
 	c[0] = &t.Sheet
 	for _, tile := range t.Map {
 		c = append(c, tile)
@@ -152,4 +152,4 @@ type AnimatedTile struct {
 func (a *AnimatedTile) Cell() int { return a.anim.Cell() }
 
 // Scan returns a.anim.
-func (a *AnimatedTile) Scan() []interface{} { return []interface{}{a.anim} }
+func (a *AnimatedTile) Scan() Components { return Components{a.anim} }

engine/walls.go

@@ -61,8 +61,8 @@ func (w *Wall) CollidesWith(b geom.Box) bool {
 }
 
 // Scan returns the Sheet and all WallUnits.
-func (w *Wall) Scan() []interface{} {
-	c := make([]interface{}, 1, len(w.Units)+1)
+func (w *Wall) Scan() Components {
+	c := make(Components, 1, len(w.Units)+1)
 	c[0] = &w.Sheet
 	for _, unit := range w.Units {
 		c = append(c, unit)
@@ -103,7 +103,7 @@ func (u *WallUnit) Draw(screen *ebiten.Image, opts *ebiten.DrawImageOptions) {
 }
 
 // Scan returns the Tile.
-func (u *WallUnit) Scan() []interface{} { return []interface{}{u.Tile} }
+func (u *WallUnit) Scan() Components { return Components{u.Tile} }
 
 func (u *WallUnit) Transform() (opts ebiten.DrawImageOptions) {
 	opts.GeoM.Translate(geom.CFloat(

game/aw.go

@@ -125,7 +125,14 @@ func (aw *Awakeman) realUpdate() error {
 			}); err != nil {
 				return err
 			}
-			aw.game.Register(bubble, aw.game.Parent(aw))
+			par := aw.game.Parent(aw)
+			for p := interface{}(aw); p != nil; p = aw.game.Parent(p) {
+				if r, ok := p.(engine.Registrar); ok {
+					if err := r.Register(bubble, par); err != nil {
+						return err
+					}
+				}
+			}
 			if err := engine.PreorderWalk(bubble, func(c, _ interface{}) error {
 				if p, ok := c.(engine.Prepper); ok {
 					return p.Prepare(aw.game)
@@ -268,7 +275,9 @@ func (aw *Awakeman) Prepare(game *engine.Game) error {
 	return nil
 }
 
-func (aw *Awakeman) Scan() []interface{} { return []interface{}{&aw.Sprite} }
+func (aw *Awakeman) Scan() engine.Components {
+	return engine.Components{&aw.Sprite}
+}
 
 func (aw *Awakeman) String() string {
 	return fmt.Sprintf("Awakeman@%v", aw.Sprite.Actor.Pos)

game/bubble.go

@@ -9,6 +9,12 @@ import (
 	"drjosh.dev/gurgle/geom"
 )
 
+var _ interface {
+	engine.Scanner
+	engine.Prepper
+	engine.Updater
+} = &Bubble{}
+
 type Bubble struct {
 	Life   int
 	Sprite engine.Sprite
@@ -49,8 +55,8 @@ func NewBubble(pos geom.Int3) *Bubble {
 	}
 }
 
-func (b *Bubble) Scan() []interface{} {
-	return []interface{}{&b.Sprite}
+func (b *Bubble) Scan() engine.Components {
+	return engine.Components{&b.Sprite}
 }
 
 func (b *Bubble) String() string {

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)),
-		Components: []interface{}{
+		Components: engine.Components{
 			&engine.Parallax{
 				CameraID: "game_camera",
 				Child: &engine.Billboard{

main.go

@@ -68,14 +68,14 @@ func main() {
 			Z: math.Sqrt(3),
 		},
 		Root: &engine.DrawDFS{
-			Components: []interface{}{
+			Components: engine.Components{
 				&engine.Fill{
 					ID:    "bg_fill",
 					Color: color.Gray{100},
 				},
 				&engine.DrawDAG{
 					ChunkSize: 16,
-					Components: []interface{}{
+					Components: engine.Components{
 						&engine.Camera{
 							ID:    "game_camera",
 							Child: lev1,