walking and colliding

engine/actor.go

@@ -2,14 +2,15 @@ package engine
 
 import (
 	"encoding/gob"
-	"errors"
+	"fmt"
 	"image"
 )
 
 // Ensure Actor satisfies interfaces.
-var _ Prepper = &Actor{}
-
-var errCollision = errors.New("collision detected")
+var _ interface {
+	Bounder
+	Prepper
+} = &Actor{}
 
 func init() {
 	gob.Register(&Actor{})
@@ -28,14 +29,17 @@ type Actor struct {
 	xRem, yRem      float64
 }
 
+func (a *Actor) BoundingRect() image.Rectangle { return image.Rectangle{a.Pos, a.Pos.Add(a.Size)} }
+
 func (a *Actor) CollidesAt(p image.Point) bool {
-	return nil != Walk(a.collisionDomain, func(c interface{}) error {
+	bounds := image.Rectangle{Min: p, Max: p.Add(a.Size)}
+	return nil != Walk(a.collisionDomain, func(c interface{}, _ []interface{}) error {
 		coll, ok := c.(Collider)
 		if !ok {
 			return nil
 		}
-		if coll.CollidesWith(image.Rectangle{Min: p, Max: p.Add(a.Size)}) {
-			return errCollision
+		if coll.CollidesWith(bounds) {
+			return Collision{With: coll}
 		}
 		return nil
 	})
@@ -91,3 +95,13 @@ func sign(m int) int {
 	}
 	return 1
 }
+
+// Collision reports a collision occurred.
+type Collision struct {
+	With Collider
+}
+
+// Error is really only to implement the error interface.
+func (c Collision) Error() string {
+	return fmt.Sprintf("collision with %v", c.With)
+}

engine/game.go

@@ -23,8 +23,13 @@ type Game struct {
 	ScreenHeight int
 	Root         DrawUpdater // typically a *Scene or SceneRef though
 
+	// Components by ID
 	dbmu sync.RWMutex
 	db   map[string]interface{}
+
+	// Collision domains - all Collider subcomponents
+	cdmu sync.RWMutex
+	cd   map[string]map[Collider]struct{}
 }
 
 // Draw draws the entire thing, with default draw options.
@@ -93,53 +98,63 @@ func (g *Game) Component(id string) interface{} {
 // Scan implements Scanner.
 func (g *Game) Scan() []interface{} { return []interface{}{g.Root} }
 
-// Walk calls v with every component reachable from c via Scan, recursively,
-// for as long as visit returns nil.
-func Walk(c interface{}, v func(interface{}) error) error {
-	if err := v(c); err != nil {
+// Walk calls v with every path of components reachable from c via Scan, for as
+// long as visit returns nil.
+func Walk(c interface{}, v func(interface{}, []interface{}) error) error {
+	return walk(c, nil, v)
+}
+
+func walk(c interface{}, p []interface{}, v func(interface{}, []interface{}) error) error {
+	if err := v(c, p); err != nil {
 		return err
 	}
 	sc, ok := c.(Scanner)
 	if !ok {
 		return nil
 	}
+	p = append(p, c)
 	for _, c := range sc.Scan() {
-		if err := Walk(c, v); err != nil {
+		if err := walk(c, p, v); err != nil {
 			return err
 		}
 	}
 	return nil
 }
 
-// Load calls Load on all Loaders reachable via Scan (using Walk).
-// It stops on the first error.
-func (g *Game) Load(assets fs.FS) error {
-	return Walk(g.Root, func(c interface{}) error {
+// LoadAndPrepare first calls Load on all Loaders. Once loading is complete,
+// it builds the component database and then calls Prepare on every Preparer.
+//  You must call Prepare before any calls
+// to Component. You may call Prepare again (e.g. as an alternative to
+// fastidiously calling RegisterComponent/UnregisterComponent).
+func (g *Game) LoadAndPrepare(assets fs.FS) error {
+	if err := Walk(g.Root, func(c interface{}, _ []interface{}) error {
 		l, ok := c.(Loader)
 		if !ok {
 			return nil
 		}
 		return l.Load(assets)
-	})
-}
+	}); err != nil {
+		return err
+	}
+
+	g.cdmu.Lock()
+	g.cd = make(map[string]map[Collider]struct{})
+	g.cdmu.Unlock()
 
-// Prepare builds the component database (using Walk) and then calls
-// Prepare on every Preparer. You must call Prepare before any calls
-// to Component. You may call Prepare again (e.g. as an alternative to
-// fastidiously calling RegisterComponent/UnregisterComponent).
-func (g *Game) Prepare() {
 	g.dbmu.Lock()
 	g.db = make(map[string]interface{})
 	g.dbmu.Unlock()
-	// Moment in time where db is empty... whatev.
-	Walk(g.Root, func(c interface{}) error {
+
+	// -> here <- is the moment in time where db is empty.
+	Walk(g.Root, func(c interface{}, p []interface{}) error {
 		g.RegisterComponent(c)
 		return nil
 	})
-	Walk(g.Root, func(c interface{}) error {
+	Walk(g.Root, func(c interface{}, _ []interface{}) error {
 		if p, ok := c.(Prepper); ok {
 			p.Prepare(g)
 		}
 		return nil
 	})
+	return nil
 }

engine/repl.go

@@ -62,11 +62,10 @@ func (g *Game) cmdSave(dst io.Writer, argv []string) {
 func (g *Game) cmdReload(dst io.Writer, assets fs.FS) {
 	g.Disable()
 	g.Hide()
-	if err := g.Load(assets); err != nil {
+	if err := g.LoadAndPrepare(assets); err != nil {
 		fmt.Fprintf(dst, "Couldn't load: %v\n", err)
 		return
 	}
-	g.Prepare()
 	g.Enable()
 	g.Show()
 }
@@ -84,11 +83,10 @@ func (g *Game) cmdTree(dst io.Writer, argv []string) {
 			return
 		}
 	}
-	var walk func(interface{}, int)
-	walk = func(c interface{}, depth int) {
+	Walk(c, func(c interface{}, p []interface{}) error {
 		indent := ""
-		if depth > 0 {
-			indent = strings.Repeat("  ", depth-1) + "↳ "
+		if len(p) > 0 {
+			indent = strings.Repeat("  ", len(p)-1) + "↳ "
 		}
 		i, ok := c.(Identifier)
 		if ok {
@@ -96,11 +94,6 @@ func (g *Game) cmdTree(dst io.Writer, argv []string) {
 		} else {
 			fmt.Fprintf(dst, "%s%T\n", indent, c)
 		}
-		if s, ok := c.(Scanner); ok {
-			for _, d := range s.Scan() {
-				walk(d, depth+1)
-			}
-		}
-	}
-	walk(c, 0)
+		return nil
+	})
 }

main.go

@@ -42,10 +42,9 @@ func main() {
 			},
 		},
 	}
-	if err := g.Load(game.Assets); err != nil {
-		log.Fatalf("Loading error: %v", err)
+	if err := g.LoadAndPrepare(game.Assets); err != nil {
+		log.Fatalf("Loading/preparing error: %v", err)
 	}
-	g.Prepare()
 
 	if runtime.GOOS != "js" {
 		// Run a repl on the console.