Fix transition panic while currently in transition

README.md

@@ -245,6 +245,10 @@ func (s *MyScene) Update() error {
 }
 ```
 
+## Acknowledgments
+
+- When switching scenes (i.e. calling `SwitchTo`, `SwitchWithTransition` or `ProcessTrigger`) while a transition is running it will immediately be canceled and the new switch will be started. To prevent this behavior use a TransitionAwareScene and prevent this methods to be called.
+
 ## Contribution
 
 Contributions are welcome! If you find a bug or have a feature request, please open an issue on GitHub. If you would like to contribute code, please fork the repository and submit a pull request.

director.go

@@ -24,6 +24,11 @@ func NewSceneDirector[T any](scene Scene[T], state T, RuleSet map[Scene[T]][]Dir
 
 // ProcessTrigger finds if a transition should be triggered
 func (d *SceneDirector[T]) ProcessTrigger(trigger SceneTransitionTrigger) {
+	if prevTransition, ok := d.current.(SceneTransition[T]); ok {
+		// previous transition is still running, end it to process trigger
+		prevTransition.End()
+	}
+
 	for _, directive := range d.RuleSet[d.current.(Scene[T])] {
 		if directive.Trigger == trigger {
 			if directive.Transition != nil {
@@ -50,11 +55,11 @@ func (d *SceneDirector[T]) ProcessTrigger(trigger SceneTransitionTrigger) {
 	}
 }
 
-func (d *SceneDirector[T]) ReturnFromTransition(scene, orgin Scene[T]) {
+func (d *SceneDirector[T]) ReturnFromTransition(scene, origin Scene[T]) {
 	if c, ok := scene.(TransitionAwareScene[T]); ok {
-		c.PostTransition(orgin.Unload(), orgin)
+		c.PostTransition(origin.Unload(), origin)
 	} else {
-		scene.Load(orgin.Unload(), d)
+		scene.Load(origin.Unload(), d)
 	}
 	d.current = scene
 }

director_test.go

@@ -78,3 +78,48 @@ func TestSceneDirector_ProcessTriggerWithTransitionAwareness(t *testing.T) {
 	rule.Transition.End()
 	assert.Equal(t, rule.Dest, director.current)
 }
+
+func TestSceneDirector_ProcessTriggerCancelling(t *testing.T) {
+	mockScene := &MockScene{}
+	mockTransition := &baseTransitionImplementation{}
+	ruleSet := make(map[Scene[int]][]Directive[int])
+
+	director := NewSceneDirector[int](mockScene, 1, ruleSet)
+
+	rule := Directive[int]{Dest: &MockScene{}, Trigger: 2, Transition: mockTransition}
+	ruleSet[mockScene] = []Directive[int]{rule}
+	director.ProcessTrigger(2)
+
+	// Assert transition is running
+	assert.Equal(t, rule.Transition, director.current)
+
+	director.ProcessTrigger(1)
+	assert.Equal(t, rule.Dest, director.current)
+}
+
+func TestSceneDirector_ProcessTriggerCancellingToNewTransition(t *testing.T) {
+	mockSceneA := &MockScene{}
+	mockSceneB := &MockScene{}
+	mockTransitionA := &baseTransitionImplementation{}
+	mockTransitionB := &baseTransitionImplementation{}
+	ruleSet := make(map[Scene[int]][]Directive[int])
+
+	director := NewSceneDirector[int](mockSceneA, 1, ruleSet)
+
+	ruleSet[mockSceneA] = []Directive[int]{
+		Directive[int]{Dest: mockSceneB, Trigger: 2, Transition: mockTransitionA},
+	}
+	ruleSet[mockSceneB] = []Directive[int]{
+		Directive[int]{Dest: mockSceneA, Trigger: 2, Transition: mockTransitionB},
+	}
+	director.ProcessTrigger(2)
+
+	// Assert transition is running
+	assert.Equal(t, mockTransitionA, director.current)
+
+	director.ProcessTrigger(2)
+	assert.Equal(t, mockTransitionB, director.current)
+
+	mockTransitionB.End()
+	assert.Equal(t, mockSceneA, director.current)
+}

examples/director/main.go

@@ -26,6 +26,7 @@ const (
 type BaseScene struct {
 	bounds image.Rectangle
 	count  State
+	active bool
 	sm     *stagehand.SceneDirector[State]
 }
 
@@ -36,10 +37,12 @@ func (s *BaseScene) Layout(w, h int) (int, int) {
 
 func (s *BaseScene) Load(st State, sm stagehand.SceneController[State]) {
 	s.count = st
+	s.active = true
 	s.sm = sm.(*stagehand.SceneDirector[State])
 }
 
 func (s *BaseScene) Unload() State {
+	s.active = false
 	return s.count
 }
 
@@ -51,15 +54,15 @@ func (s *FirstScene) Update() error {
 	if inpututil.IsMouseButtonJustPressed(ebiten.MouseButtonLeft) {
 		s.count++
 	}
-	if inpututil.IsMouseButtonJustPressed(ebiten.MouseButtonRight) {
+	if inpututil.IsMouseButtonJustPressed(ebiten.MouseButtonRight) && s.active {
 		s.sm.ProcessTrigger(Trigger)
 	}
 	return nil
 }
 
 func (s *FirstScene) Draw(screen *ebiten.Image) {
 	screen.Fill(color.RGBA{255, 0, 0, 255}) // Fill Red
-	ebitenutil.DebugPrintAt(screen, fmt.Sprintf("Count: %v, WindowSize: %s", s.count, s.bounds.Max), s.bounds.Dx()/2, s.bounds.Dy()/2)
+	ebitenutil.DebugPrintAt(screen, fmt.Sprintf("Count: %v, WindowSize: %s\nActive? %v", s.count, s.bounds.Max, s.active), s.bounds.Dx()/2, s.bounds.Dy()/2)
 }
 
 type SecondScene struct {
@@ -70,15 +73,34 @@ func (s *SecondScene) Update() error {
 	if inpututil.IsMouseButtonJustPressed(ebiten.MouseButtonLeft) {
 		s.count--
 	}
-	if inpututil.IsMouseButtonJustPressed(ebiten.MouseButtonRight) {
+	if inpututil.IsMouseButtonJustPressed(ebiten.MouseButtonRight) && s.active {
 		s.sm.ProcessTrigger(Trigger)
 	}
 	return nil
 }
 
 func (s *SecondScene) Draw(screen *ebiten.Image) {
 	screen.Fill(color.RGBA{0, 0, 255, 255}) // Fill Blue
-	ebitenutil.DebugPrintAt(screen, fmt.Sprintf("Count: %v, WindowSize: %s", s.count, s.bounds.Max), s.bounds.Dx()/2, s.bounds.Dy()/2)
+	ebitenutil.DebugPrintAt(screen, fmt.Sprintf("Count: %v, WindowSize: %s\nActive? %v", s.count, s.bounds.Max, s.active), s.bounds.Dx()/2, s.bounds.Dy()/2)
+}
+
+type ThirdScene struct {
+	BaseScene
+}
+
+func (s *ThirdScene) Update() error {
+	if inpututil.IsMouseButtonJustPressed(ebiten.MouseButtonLeft) {
+		s.count++
+	}
+	if inpututil.IsMouseButtonJustPressed(ebiten.MouseButtonRight) && s.active {
+		s.sm.ProcessTrigger(Trigger)
+	}
+	return nil
+}
+
+func (s *ThirdScene) Draw(screen *ebiten.Image) {
+	screen.Fill(color.RGBA{0, 255, 0, 255}) // Fill Green
+	ebitenutil.DebugPrintAt(screen, fmt.Sprintf("Count: %v, WindowSize: %s\nActive? %v", s.count, s.bounds.Max, s.active), s.bounds.Dx()/2, s.bounds.Dy()/2)
 }
 
 func main() {
@@ -90,16 +112,30 @@ func main() {
 
 	s1 := &FirstScene{}
 	s2 := &SecondScene{}
-	trans := stagehand.NewSlideTransition[State](stagehand.BottomToTop, 0.05)
+	s3 := &ThirdScene{}
+	trans := stagehand.NewSlideTransition[State](stagehand.BottomToTop, 0.02)
+	trans2 := stagehand.NewSlideTransition[State](stagehand.TopToBottom, 0.02)
+	trans3 := stagehand.NewSlideTransition[State](stagehand.LeftToRight, 0.02)
 	rs := map[stagehand.Scene[State]][]stagehand.Directive[State]{
-		s1: []stagehand.Directive[State]{
-			stagehand.Directive[State]{Dest: s2, Trigger: Trigger},
+		s1: {
+			stagehand.Directive[State]{
+				Dest:       s2,
+				Trigger:    Trigger,
+				Transition: trans,
+			},
 		},
-		s2: []stagehand.Directive[State]{
+		s2: {
+			stagehand.Directive[State]{
+				Dest:       s3,
+				Trigger:    Trigger,
+				Transition: trans2,
+			},
+		},
+		s3: {
 			stagehand.Directive[State]{
 				Dest:       s1,
 				Trigger:    Trigger,
-				Transition: trans,
+				Transition: trans3,
 			},
 		},
 	}

manager.go

@@ -14,13 +14,21 @@ func NewSceneManager[T any](scene Scene[T], state T) *SceneManager[T] {
 
 // Scene Switching
 func (s *SceneManager[T]) SwitchTo(scene Scene[T]) {
+	if prevTransition, ok := s.current.(SceneTransition[T]); ok {
+		// previous transition is still running, end it first
+		prevTransition.End()
+	}
 	if c, ok := s.current.(Scene[T]); ok {
 		scene.Load(c.Unload(), s)
 		s.current = scene
 	}
 }
 
 func (s *SceneManager[T]) SwitchWithTransition(scene Scene[T], transition SceneTransition[T]) {
+	if prevTransition, ok := s.current.(SceneTransition[T]); ok {
+		// previous transition is still running, end it to start the next transition
+		prevTransition.End()
+	}
 	sc := s.current.(Scene[T])
 	transition.Start(sc, scene, s)
 	if c, ok := sc.(TransitionAwareScene[T]); ok {
@@ -31,11 +39,11 @@ func (s *SceneManager[T]) SwitchWithTransition(scene Scene[T], transition SceneT
 	s.current = transition
 }
 
-func (s *SceneManager[T]) ReturnFromTransition(scene, orgin Scene[T]) {
+func (s *SceneManager[T]) ReturnFromTransition(scene, origin Scene[T]) {
 	if c, ok := scene.(TransitionAwareScene[T]); ok {
-		c.PostTransition(orgin.Unload(), orgin)
+		c.PostTransition(origin.Unload(), origin)
 	} else {
-		scene.Load(orgin.Unload(), s)
+		scene.Load(origin.Unload(), s)
 	}
 	s.current = scene
 }

transition.go

@@ -50,7 +50,7 @@ func (t *BaseTransition[T]) Layout(outsideWidth, outsideHeight int) (int, int) {
 
 // Ends transition to the next scene
 func (t *BaseTransition[T]) End() {
-	t.sm.ReturnFromTransition(t.toScene.(Scene[T]), t.fromScene.(Scene[T]))
+	t.sm.ReturnFromTransition(t.toScene, t.fromScene)
 }
 
 type FadeTransition[T any] struct {

transition_test.go

@@ -104,6 +104,35 @@ func TestBaseTransition_Awareness(t *testing.T) {
 	assert.True(t, to.postTransitionCalled)
 }
 
+func TestBaseTransition_SwitchCanceling(t *testing.T) {
+	from := &MockScene{}
+	to := &MockScene{}
+	trans := &baseTransitionImplementation{}
+	sm := NewSceneManager[int](from, 0)
+	sm.SwitchWithTransition(to, trans)
+
+	// Assert transition is running
+	assert.Equal(t, trans, sm.current)
+
+	sm.SwitchTo(to)
+	assert.Equal(t, to, sm.current)
+}
+
+func TestBaseTransition_TransitionCanceling(t *testing.T) {
+	from := &MockScene{}
+	to := &MockScene{}
+	transA := &baseTransitionImplementation{}
+	transB := &baseTransitionImplementation{}
+	sm := NewSceneManager[int](from, 0)
+	sm.SwitchWithTransition(to, transA)
+
+	// Assert transition is running
+	assert.Equal(t, transA, sm.current)
+
+	sm.SwitchWithTransition(to, transB)
+	assert.Equal(t, transB, sm.current)
+}
+
 func TestFadeTransition_UpdateOncePerFrame(t *testing.T) {
 	var value float32 = .6
 	from := &MockScene{}