minor refactoring

engine/game.go

@@ -455,6 +455,16 @@ func concatOpts(a, b ebiten.DrawImageOptions) ebiten.DrawImageOptions {
 // recursive operations, return Skip for components that should be skipped.
 type VisitFunc func(interface{}) error
 
+// Many calls a VisitFunc for multiple args, and returns on first non-nil error.
+func (v VisitFunc) Many(x ...interface{}) error {
+	for _, c := range x {
+		if err := v(c); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // Skip is an "error" value that can be returned from visitor callbacks. It
 // tells recursive methods of Game to skip processing the current item and its
 // descendants, but will otherwise continue processing.

engine/sprite.go

@@ -58,10 +58,7 @@ func (s *Sprite) Draw(screen *ebiten.Image, opts *ebiten.DrawImageOptions) {
 
 // Scan visits &s.Actor and &s.Sheet.
 func (s *Sprite) Scan(visit VisitFunc) error {
-	if err := visit(&s.Actor); err != nil {
-		return err
-	}
-	return visit(&s.Sheet)
+	return visit.Many(&s.Actor, &s.Sheet)
 }
 
 // Anim returns the current Anim.

example/aw.go

@@ -119,7 +119,7 @@ func (aw *Awakeman) realUpdate() error {
 		ε              = 0.2
 		restitution    = -0.3
 		gravity        = 0.25
-		airResistance  = -0.005 // ⇒ terminal velocity = 10
+		airResistance  = -0.005
 		jumpVelocity   = -3.3
 		sqrt2          = 1.414213562373095
 		runVelocity    = sqrt2

example/level1.go

@@ -45,7 +45,16 @@ func Level1() *engine.Scene {
 			&engine.DrawDAG{
 				ChunkSize: 16,
 				Child: engine.MakeContainer(
-					&engine.PrismMap{
+					level1PrismMap(),
+					level1Awakeman(),
+				), // Container
+			}, // DrawDAG
+		), // Container
+	} // Scene
+}
+
+func level1PrismMap() *engine.PrismMap {
+	return &engine.PrismMap{
 		ID: "hexagons",
 		PosToWorld: geom.IntMatrix3x4{
 			// For each tile in the X direction, go right by 24 and
@@ -271,8 +280,11 @@ func Level1() *engine.Scene {
 
 			geom.Pt3(0, 0, 13): {},
 		}, // Map
-					}, // PrismMap
-					&Awakeman{
+	} // PrismMap
+}
+
+func level1Awakeman() *Awakeman {
+	return &Awakeman{
 		CameraID: "game_camera",
 		ToastID:  "toast",
 		Sprite: engine.Sprite{
@@ -332,9 +344,5 @@ func Level1() *engine.Scene {
 				Src:      engine.ImageRef{Path: "assets/aw.png"},
 			}, // Sheet
 		}, // Sprite
-					}, // Awakeman
-				), // Container
-			}, // DrawDAG
-		), // Container
-	} // Scene
+	} // Awakeman
 }