error-based walk; Scener

engine/actor.go

@@ -2,12 +2,15 @@ package engine
 
 import (
 	"encoding/gob"
+	"errors"
 	"image"
 )
 
 // Ensure Actor satisfies interfaces.
 var _ Prepper = &Actor{}
 
+var errCollision = errors.New("collision detected")
+
 func init() {
 	gob.Register(Actor{})
 }
@@ -26,17 +29,16 @@ type Actor struct {
 }
 
 func (a *Actor) CollidesAt(p image.Point) bool {
-	hit := false
+	return nil != Walk(a.collisionDomain, func(c interface{}) error {
-	Walk(a.collisionDomain, func(c interface{}) bool {
+		coll, ok := c.(Collider)
-		if coll, ok := c.(Collider); ok {
+		if !ok {
+			return nil
+		}
 		if coll.CollidesWith(image.Rectangle{Min: p, Max: p.Add(a.Size)}) {
-				hit = true
+			return errCollision
-				return false
 		}
-		}
+		return nil
-		return true
 	})
-	return hit
 }
 
 func (a *Actor) MoveX(dx float64, onCollide func()) {

engine/asset.go

@@ -19,6 +19,9 @@ var (
 	AnimDefs map[string]*AnimDef
 
 	imageCache = make(map[string]*ebiten.Image)
+
+	// Ensure SceneRef does the same stuff as Scene.
+	_ Scener = &SceneRef{}
 )
 
 // AnimRef manages an Anim using a premade AnimDef from the cache.
@@ -78,26 +81,37 @@ func (r *ImageRef) Image() *ebiten.Image {
 type SceneRef struct {
 	Path string
 
-	scene *Scene
+	scene *Scene // not exported for gob reasons
 }
 
-func (r *SceneRef) Scene() *Scene {
+// Load loads the scene from the file and then calls Load
-	if r.scene != nil {
+// on the freshly-loaded Scene.
-		return r.scene
+func (r *SceneRef) Load() error {
-	}
 	f, err := AssetFS.Open(r.Path)
 	if err != nil {
-		log.Fatalf("Couldn't open asset: %v", err)
+		return err
 	}
 	defer f.Close()
 
 	gz, err := gzip.NewReader(f)
 	if err != nil {
-		log.Fatalf("Couldn't gunzip asset: %v", err)
+		return err
 	}
-	r.scene = new(Scene)
+	sc := new(Scene)
-	if err := gob.NewDecoder(gz).Decode(r.scene); err != nil {
+	if err := gob.NewDecoder(gz).Decode(sc); err != nil {
-		log.Fatalf("Couldn't decode asset: %v", err)
+		return err
 	}
-	return r.scene
+	r.scene = sc
+	return sc.Load()
 }
+
+// Implement Scener by forwarding all the other calls to r.scene
+
+func (r SceneRef) Draw(screen *ebiten.Image, opts ebiten.DrawImageOptions) {
+	r.scene.Draw(screen, opts)
+}
+func (r SceneRef) DrawOrder() float64  { return r.scene.DrawOrder() }
+func (r SceneRef) Ident() string       { return r.scene.Ident() }
+func (r SceneRef) Prepare(g *Game)     { r.scene.Prepare(g) }
+func (r SceneRef) Scan() []interface{} { return r.scene.Scan() }
+func (r SceneRef) Update() error       { return r.scene.Update() }

engine/game.go

@@ -10,21 +10,11 @@ func init() {
 	gob.Register(Game{})
 }
 
-type GameMode int
-
-const (
-	GameModeMenu = GameMode(iota)
-	GameModePlay
-	GameModePause
-	GameModeEdit
-)
-
 // Game implements the ebiten methods using a collection of components.
 type Game struct {
-	Mode         GameMode
 	ScreenWidth  int
 	ScreenHeight int
-	*Scene
+	Scene        *Scene
 
 	componentsByID map[string]interface{}
 }
@@ -79,21 +69,21 @@ func (g *Game) Component(id string) interface{} { return g.componentsByID[id] }
 func (g *Game) Scan() []interface{} { return []interface{}{g.Scene} }
 
 // Walk calls v with every component reachable from c via Scan, recursively,
-// for as long as visit returns true.
+// for as long as visit returns nil.
-func Walk(c interface{}, v func(interface{}) bool) {
+func Walk(c interface{}, v func(interface{}) error) error {
-	if !v(c) {
+	if err := v(c); err != nil {
-		return
+		return err
 	}
 	sc, ok := c.(Scanner)
 	if !ok {
-		return
+		return nil
 	}
 	for _, c := range sc.Scan() {
-		if !v(c) {
+		if err := Walk(c, v); err != nil {
-			return
+			return err
 		}
-		Walk(c, v)
 	}
+	return nil
 }
 
 // PrepareToRun builds the component database (using Walk) and then calls
@@ -101,14 +91,14 @@ func Walk(c interface{}, v func(interface{}) bool) {
 // ebiten.RunGame.
 func (g *Game) PrepareToRun() {
 	g.componentsByID = make(map[string]interface{})
-	Walk(g, func(c interface{}) bool {
+	Walk(g, func(c interface{}) error {
 		g.RegisterComponent(c)
-		return true
+		return nil
 	})
-	Walk(g, func(c interface{}) bool {
+	Walk(g, func(c interface{}) error {
 		if p, ok := c.(Prepper); ok {
 			p.Prepare(g)
 		}
-		return true
+		return nil
 	})
 }

engine/interface.go

@@ -29,6 +29,12 @@ type Identifier interface {
 	Ident() string
 }
 
+// Loader components get the chance to load themselves. This happens
+// before preparation.
+type Loader interface {
+	Load() error
+}
+
 // ParallaxScaler components have a scaling factor. This is used for
 // parallax layers in a scene, and can be thought of as 1/distance.
 type ParallaxScaler interface {
@@ -49,6 +55,18 @@ type Scanner interface {
 	Scan() []interface{}
 }
 
+// Scener components do everything that a Scene can. The other implementation
+// is SceneRef.
+type Scener interface {
+	Drawer
+	DrawOrderer
+	Identifier
+	Loader
+	Prepper
+	Scanner
+	Updater
+}
+
 // Updater components can update themselves. Update is called repeatedly.
 // Each component is responsible for calling Update on its child components
 // (so that disabling the parent prevents updates to the children, etc).

engine/scene.go

@@ -9,15 +9,8 @@ import (
 	"github.com/hajimehoshi/ebiten/v2"
 )
 
-// Ensure Scene satisfies interfaces.
+// Ensure Scene satisfies Scener.
-var (
+var _ Scener = &Scene{}
-	_ Identifier  = &Scene{}
-	_ Drawer      = &Scene{}
-	_ DrawOrderer = &Scene{}
-	_ Prepper     = &Scene{}
-	_ Scanner     = &Scene{}
-	_ Updater     = &Scene{}
-)
 
 func init() {
 	gob.Register(Scene{})
@@ -46,6 +39,20 @@ func (s *Scene) Draw(screen *ebiten.Image, opts ebiten.DrawImageOptions) {
 	}
 }
 
+// Load loads any components that need loading.
+func (s *Scene) Load() error {
+	for _, i := range s.Components {
+		l, ok := i.(Loader)
+		if !ok {
+			continue
+		}
+		if err := l.Load(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // Prepare does an initial Z-order sort.
 func (s *Scene) Prepare(game *Game) { s.sortByDrawOrder() }