Support ispx with generics (#312)

* simplify `Gopt_Game_Gopx_GetWidget`

* split getWidget

* make `getAllShapes` private

game.go

@@ -112,7 +112,6 @@ type Spriter interface {
 }
 type Gamer interface {
 	initGame(sprites []Spriter) *Game
-	getGame() *Game
 }
 
 func (p *Game) IsRunned() bool {
@@ -1351,32 +1350,38 @@ func (p *Game) ShowVar(name string) {
 	p.setStageMonitor("", getVarPrefix+name, true)
 }
 
+func (p *Game) getAllShapes() []Shape {
+	return p.items
+}
+
 // -----------------------------------------------------------------------------
 // Widget
 
-// GetWidget returns the widget instance with given name. It panics if not found.
-func Gopt_Game_Gopx_GetWidget[T any](game interface{}, name string) *T {
-	var gamePtr *Game
-	switch ptr := game.(type) {
-	case *Game:
-		gamePtr = ptr
-	case interface{ Parent() *Game }:
-		gamePtr = ptr.Parent()
-	case Gamer:
-		gamePtr = ptr.getGame()
-	default:
-		panic("GetWidget: unexpected game type" + reflect.TypeOf(game).String())
-	}
-	items := gamePtr.items
+type ShapeGetter interface {
+	getAllShapes() []Shape
+}
+
+// GetWidget_ returns the widget instance with given name. It panics if not found.
+// Instead of being used directly, it is meant to be called by `Gopt_Game_Gopx_GetWidget` only.
+// We extract `GetWidget_` to keep `Gopt_Game_Gopx_GetWidget` simple, which simplifies work in ispx,
+// see details in https://github.com/goplus/builder/issues/765#issuecomment-2313915805.
+func GetWidget_(sg ShapeGetter, name string) Widget {
+	items := sg.getAllShapes()
 	for _, item := range items {
 		widget, ok := item.(Widget)
 		if ok && widget.GetName() == name {
-			if result, ok := widget.(interface{}).(*T); ok {
-				return result
-			} else {
-				panic("GetWidget: type mismatch - expected " + reflect.TypeOf((*T)(nil)).Elem().String() + ", got " + reflect.TypeOf(widget).String())
-			}
+			return widget
 		}
 	}
 	panic("GetWidget: widget not found - " + name)
 }
+
+// GetWidget returns the widget instance (in given type) with given name. It panics if not found.
+func Gopt_Game_Gopx_GetWidget[T any](sg ShapeGetter, name string) *T {
+	widget := GetWidget_(sg, name)
+	if result, ok := widget.(interface{}).(*T); ok {
+		return result
+	} else {
+		panic("GetWidget: type mismatch")
+	}
+}

sprite.go

@@ -111,6 +111,10 @@ func (p *Sprite) Parent() *Game {
 	return p.g
 }
 
+func (p *Sprite) getAllShapes() []Shape {
+	return p.g.getAllShapes()
+}
+
 func (p *Sprite) init(
 	base string, g *Game, name string, sprite *spriteConfig, gamer reflect.Value, shared *sharedImages) {
 	if sprite.Costumes != nil {