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Enabling HUDs

The current stack manager does not allow for Heads-Up-Display overlays yet, as each time a new state is pushed to the stack, the previous state is paused. We therefor have to add the possibility to overlay states over each other.

The Stack

Overlaying States

To add a new overlay, we simply push the new state to the stack:

util::Expected<void> DirectXApp::overlayGameState(GameState* const gameState)
{
  // push new game state
  gameStates.push_back(gameState);
  if (!(*gameStates.rbegin())->initialize().wasSuccessful())
    return std::runtime_error("Critical error: Unable to shut the game state down!");


  // return success
  return { };
}

Pushing States

Now when pushing a new state to the stack, we have to pause all underlying states:

util::Expected<void> DirectXApp::pushGameState(GameState* const gameState)
{
  // pause the current state
  for (std::deque<GameState*>::reverse_iterator it = gameStates.rbegin(); it != gameStates.rend(); it++)
    if (!(*it)->pause().wasSuccessful())
      return std::runtime_error("Critical error: Unable to resume the game state");


  // push and initialize the new game state
  gameStates.push_back(gameState);
  if (!(*gameStates.rbegin())->initialize().wasSuccessful())
    return std::runtime_error("Critical error: Unable to initialize the game state!");


  // return success
  return { };
}

Popping States

When popping a state from the stack, we have to resume all underlying states:

util::Expected<void> DirectXApp::popGameState()
{
  // shut the current state down
  if (!gameStates.empty())
  {
    if (!(*gameStates.rbegin())->shutdown().wasSuccessful())
      return std::runtime_error("Critical error: Unable to shut the game state down!");
    gameStates.pop_back();
  }


  // resume previous states
  for (std::deque<GameState*>::reverse_iterator it = gameStates.rbegin(); it != gameStates.rend(); it++)
    if (!(*it)->resume().wasSuccessful())
      return std::runtime_error("Critical error: Unable to resume the game state");


  // return success
  return { };
}

A Barebone HUD

I created a blank HUD state that simply writes its name to the bottom of the screen. The main playState then initializes its own HUD:

util::Expected<void> PlayState::initialize()
{
    ...


    // initialize the game overlay
  dxApp->overlayGameState(&UI::HeadsUpDisplayState::createInstance(dxApp, L"HUD"));


  ...
}

And that’s it. Our Stack Manager now supports HUDs.

HUD

HUD2

This concludes our first series of tutorials about state stacks. You can download the source code from here.

References

Literature

(in alphabetic order)

  • Game Programming Algorithms, by Sanjay Madhav
  • Game Programming Patterns, by Robert Nystrom
  • Microsoft Developer Network (MSDN)
  • Tricks of the Windows Game Programming Gurus, by André LaMothe
  • Wikipedia

Art