Keeping everything within one Activity

Question

Overview

My game is currently based on a single activity (rather than multiple activities) and I would like to keep it that way.

At the moment, it goes straight into the game at level 1. I will shortly be adding an options menu and another 20 or so levels. (As well as a high-score screen, help screen etc).

The thing I'm not sure about is, how do I tell the app/renderer what screen/part of the game to render?

It's an openGL ES 2.0 app so at the moment, the method I have in my mind is something like this:

Code Snippets

int level = 0;  //0 means menu, 1 means level 1 etc

in onDrawFrame(); have something like this:

@Override
public void onDrawFrame(GL10 gl) {

switch (level){

case 0:renderMenu();break;
case 1:renderLevel1();break
case 2............

And so on.

I would also do the same with the logic updating.

Is this the way to go? I'm just not sure it's very efficient but I can't really see what the alternatives are - another way I was looking into was having a separate GLRenderer for each 'screen / level' but this seems much more over-kill.

Would appreciate some guidance as to how to display the correct screen / level at the right time.

Edit This is the current structure of my code:

Activity class

public class MainActivity extends Activity {

//Various pieces of code here

    class MyGLSurfaceView extends GLSurfaceView {

    //Various pieces of code here

    @Override
    public boolean onTouchEvent(MotionEvent event) {

    //Touch events handles here

}

GL Renderer class

onDrawFrame(){

    render();
    update();
}

Answer 1

You are asking for a concept of scenes inside one activity. This is as easy as creating an abstract scene or an interface that will have methods like renderMe() and onUpdate(long timeElapsed). Then in your engine or game-loop you simply render the current scene. How do you switch between scenes is upto you. You can have a governing class SceneManager. So how is this gonna work?

Scene concept:

interface Scene {
  void renderMe(); // do the graphics rendering
  onUpdate(long timeElapsed); // update positions etc
  onTouch(MotionEvent e); // handle user input
}

class MyScene implements Scene {
  // implement rendering and update methods, you can pass in the activity and GLSurfaceView (in constructor or some injection)
}

Your game loop should look like this:

void loop() {
  while(running) {
    long timeStampBegin = getCurrentTime();
    SceneManager.getInstance().getCurrentScene().renderMe();
    SceneManager.getInstance().getCurrentScene().onUpdate(getCurrentTime() - timeStampBegin);
  }
}

And then when you switch your scenes by calling SceneManager.setCurrentScene(), your loop will just start rendering something else. SceneManager can be a singleton class or simply a class with static reference to the scene.

SceneManager concept (singleton):

class SceneManager {

  private static SceneManager INSTANCE = new SceneManager();

  private Scene currentScene;

  public static SceneManager getInstance() {
    return INSTANCE;
  }

  public Scene getCurrentScene() {
    return currentScene;
  }

  public void setCurrentScene(Scene scene) {
    currentScene = scene;
  }
}

You also have to implement the onTouchEvent in GLSurfaceView and pass the event to your scene to be able to handle touch events. This happens in separate thread, so it is not part of your loop.

This should be enough to create skeleton one-activity-multiple-scene model.