call it "scene"

engine/game.go

@@ -6,12 +6,12 @@ import "github.com/hajimehoshi/ebiten/v2"
 type Game struct {
 	ScreenWidth  int
 	ScreenHeight int
-	Layers       *Layers
+	Scene        *Scene
 }
 
 // Draw draws the entire thing.
 func (g *Game) Draw(screen *ebiten.Image) {
-	g.Layers.Draw(screen, ebiten.GeoM{})
+	g.Scene.Draw(screen, ebiten.GeoM{})
 }
 
 // Layout returns the configured screen width/height.
@@ -21,5 +21,5 @@ func (g *Game) Layout(outsideWidth, outsideHeight int) (w, h int) {
 
 // Update just passes the call onto Layers.
 func (g *Game) Update() error {
-	return g.Layers.Update()
+	return g.Scene.Update()
 }

engine/scene.go

@@ -21,14 +21,14 @@ type ZPositioner interface {
 	Z() float64
 }
 
-// Layers
-type Layers struct {
+// Scene manages drawing and updating a bunch of components.
+type Scene struct {
 	Components []interface{}
 	needsSort  bool
 }
 
-// Draw draws all layers in order.
-func (l *Layers) Draw(screen *ebiten.Image, geom ebiten.GeoM) {
+// Draw draws all components in order.
+func (l *Scene) Draw(screen *ebiten.Image, geom ebiten.GeoM) {
 	for _, i := range l.Components {
 		if d, ok := i.(Drawer); ok {
 			d.Draw(screen, geom)
@@ -37,13 +37,15 @@ func (l *Layers) Draw(screen *ebiten.Image, geom ebiten.GeoM) {
 }
 
 // SetNeedsSort informs l that its layers may be out of order.
-func (l *Layers) SetNeedsSort() {
+func (l *Scene) SetNeedsSort() {
 	l.needsSort = true
 }
 
 // sortByZ sorts the components by Z position.
-// Stable sort is used to avoid z-fighting among layers without a Z.
-func (l *Layers) sortByZ() {
+// Stable sort is used to avoid Z-fighting among layers without a Z, or
+// among those with equal Z. All non-ZPositioners are sorted first.
+func (l *Scene) sortByZ() {
+	l.needsSort = false
 	sort.SliceStable(l.Components, func(i, j int) bool {
 		a, aok := l.Components[i].(ZPositioner)
 		b, bok := l.Components[j].(ZPositioner)
@@ -52,11 +54,10 @@ func (l *Layers) sortByZ() {
 		}
 		return !aok && bok
 	})
-	l.needsSort = false
 }
 
 // Update calls Update on all Updater components.
-func (l *Layers) Update() error {
+func (l *Scene) Update() error {
 	for _, c := range l.Components {
 		if u, ok := c.(Updater); ok {
 			if err := u.Update(); err != nil {

main.go

@@ -84,11 +84,11 @@ func main() {
 	game := &engine.Game{
 		ScreenHeight: screenHeight,
 		ScreenWidth:  screenWidth,
-		Layers: &engine.Layers{
+		Scene: &engine.Scene{
 			Components: components,
 		},
 	}
-	game.Layers.SetNeedsSort()
+	game.Scene.SetNeedsSort()
 
 	if err := ebiten.RunGame(game); err != nil {
 		log.Fatalf("Game error: %v", err)