Game Engine Loop: Functions and Components

• Game State Manager and Function Pointers

Game Engine Design

• Any application involves a general initialization followed by a loop until the user quits.
• The loop manages input, game logic, and screen reflection.
• In games, its referred to as the "game loop".
• When the loop ends, there's a "freeing" part that releases loaded data.
• Data loaded within the game loop should be released before exiting to maintain code consistency and improve stability.
• Data loaded in one component should be released in that same component upon exiting.

System Component Management

• Game code needs to initialize system components before entering game code and the game loop.
• Such components establish necessary hardware functionalities and are used later in the game.
• Examples include setting up an input, video, and audio devices, allocating video buffers, and deciding hardware/software division of the pipeline.
• System component initialization should be done just once.
• If a component fails to initialize, the game quits with an error.
• If all system components initialize correctly, frame rate controller and game state variables are then initialized.
• Devices that were allocated should be released the game loop.
• Input device allocations during the initialization stage should be released upon exiting the application.

Game Loop

• Following hardware component initialization, the application enters the game loop.
• The process will keep looping until a specific game exit condition is met.
• Load Current State: This involves loading all of the state's data, assuming that a restart is not in progress.
• Resets the frame rate controller
• Initialize Current State: Make all state data ready for the first time.
• State Loop: A conditional loop continues running until the game switches to a new state or the current state is reset.
• Frees current state upon exit.
• Unload state data when not restarting.

Handling Game States

• State Switching: Games switch to a new state until another switch is needed.
• Reasons for switching include level completion, losing, or pressing a key.
• Restarting a state qualifies as a state switch. Special care is taken to avoid unloading or reloading data when a state is restarted.
• A state loop exists within the game loop so a state should have its loop
• The condition to break out of the state loop is to set the next-wanted state indicator to a different state than the current one.
• When the next state is requested, the game runs the current state until the end of the current frame.
• State switch occurs at the next state loop condition check.

Loading/Unloading

• Every state should load data upon entering and exiting.
• Each state uses distinct elements such as backgrounds, sprites, animations, and sound effects,
• Data loading/unloading is slow due to disk files so it is completed in loading or introduction levels.
• Outside the state loop, loading/unloading state data should occur.
• CPU and GPU power is spent updating and rendering the game within the state loop without being wasted on loading/unloading data.

State Restarting

• Restarting a state resembles switching to a different state in the initial steps.
• The next state indicator can be set to “RESTART”, and therefore break the state loop.
• Condition checks prevent game data from unloading/reloading unlike switching to another state.
• Calls its free and initialize functions - resetting the state's is not specific to restarting.

System Components

• Game state manager was explained previously.
• Frame rate controller assists consistent game speed.

Frame Rate Controller

• The amount of time needed to complete 1 frame in games (updating objects, AI, collisions, physics, input, rendering) is extremely inconsistent.
• Influenced by factors like detail level, number of visible objects, effects, AI depth, collision types and physics iterations.
• Frame rate controller ensures running a consistent speed.
• Each frame requires a specific pre-set amount of time.
• The check is to see how much time the current from took occurs at the beginning of each time.
• If a frame completes quicker than the pre-set amount: the game "waits" by creating an empty loop until the time is met.
• If a frame takes longer, optimize by avoiding rendering objects and reduce the number of effects used.
• The frame rate controller can include functionalities like count the number of frames since the game or current state started, and track how much time the last frame used.
• Because beginning and ending time is important, the frame rate controller should be called at those points.
• Minimum time for the system is 1 millisecond.