Added scene system.

game.go

@@ -90,6 +90,12 @@ func Stop() {
 }
 
 func cleanup() {
+	// cleanup scenes
+	for _, scene := range scenes {
+		scene.Cleanup()
+	}
+
+	// cleanup systems
 	for _, system := range systems {
 		system.Cleanup()
 	}

scene.go

@@ -0,0 +1,103 @@
+package goga
+
+// A scene used to switch between game states.
+// The Cleanup() method is called when a scene is removed
+// or the program is stopped. It can be used to cleanup open resources
+// (like GL objects).
+type Scene interface {
+	Pause()
+	Resume()
+	Cleanup()
+	Resize(int, int)
+	GetName() string
+}
+
+var (
+	scenes      []Scene
+	activeScene Scene
+)
+
+// Adds a scene to game.
+// Returns false if the scene exists already.
+func AddScene(scene Scene) bool {
+	for _, s := range scenes {
+		if s == scene {
+			return false
+		}
+	}
+
+	scenes = append(scenes, scene)
+
+	return true
+}
+
+// Removes a given scene.
+// Returns false if it could not be found.
+func RemoveScene(scene Scene) bool {
+	for i, s := range scenes {
+		if s == scene {
+			s.Cleanup()
+			scenes = append(scenes[:i], scenes[i+1:]...)
+			return true
+		}
+	}
+
+	return false
+}
+
+// Removes all scenes.
+func RemoveAllScenes() {
+	for _, s := range scenes {
+		s.Cleanup()
+	}
+
+	scenes = make([]Scene, 0)
+}
+
+// Finds and returns a scene by name, or nil if not found.
+func GetSceneByName(name string) Scene {
+	for _, s := range scenes {
+		if s.GetName() == name {
+			return s
+		}
+	}
+
+	return nil
+}
+
+// Switches to given scene.
+// This will pause the currently active scene.
+func SwitchScene(scene Scene) {
+	if activeScene != nil {
+		activeScene.Pause()
+	}
+
+	activeScene = scene
+
+	for _, s := range scenes {
+		if s == activeScene {
+			activeScene.Resume()
+			break
+		}
+	}
+}
+
+// Switches to given existing scene by name.
+// Returns false if the scene does not exist.
+func SwitchSceneByName(name string) bool {
+	scene := GetSceneByName(name)
+
+	if scene == nil {
+		return false
+	}
+
+	SwitchScene(scene)
+
+	return true
+}
+
+// Returns the currently active scene.
+// Can be nil if no scene was set.
+func GetActiveScene() Scene {
+	return activeScene
+}

system.go

@@ -5,7 +5,7 @@ import ()
 // A system provides logic for actors satisfying required components.
 // They are automatically updated on each frame.
 // When a system is removed from systems, the Cleanup() method will be called.
-// This will also happen on program stop. This can be used to cleanup open resources
+// This will also happen on program stop. It can be used to cleanup open resources
 // (like GL objects).
 type System interface {
 	Update(float64)