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Exercise: Navigating the code
Background: Pac-Man project
The project is split into three parts (solutions).
- libpacman - This is where the entire game lives
- pacman - This is the project that generates the executable, the only thing it does is to create the game instance
and call the
run()function - pacman_tests - All of the unit tests for the game
libpacman
The libpacman solution has 3 main parts.
- Game - A class that holds the Canvas and GameState objects
- Canvas - A class that uses the SFML library to draw objects to the screen. Also manages the game window
- GameState - A class that holds all of the state for Pac-Man. Contains classes like the Ghosts, PacMan and the Pellets PacMan eats
Updating the game state
Within the Game.cpp file there is a function called run(), this function draws the current game state to
screen canvas.update(gameState); but it only calls the game state update function at a fixed interval, it also sends
this interval to the game state update function gameState.step(delta_time);
Then in the step() function in GameState.cpp the magic happens. Each object in the game world is updated and the
state of the game world is checked. Did Pac-Man just eat a pellet? Are the ghosts touching Pac-Man? Which direction is
Pac-Man moving?
The game board
The game board is stored as a two dimensional array of integers in the Board.cpp file. The array itself is only
accessible within that file, which is why we export helper functions that use the array as a global variable. This
exporting happens in Board.hpp
Ghosts
All ghosts inherit from the parent Ghost class defined in Ghost.hpp/cpp, there are a couple of pure virtual functions
those ghosts need to implement, otherwise you are not able to create an instance of them. A ghost stores its current
location, its current target and other state regarding if it is frightened or not. At each update() call a ghost needs
to decide what its target is and which direction it should turn next.
Pac-Man
Pac-Man has similar state to a Ghost, like direction and position. Pac-Man's behavior is also similar in update() as
we need to determine where to place Pac-Man in the next game state. But the information on which direction to turn comes
from the player (or a bot).
Unit tests
Because updates of game state and drawing the game on screen are completely separate, we can create game state within
unit tests and give it arbitrary delta time and call whatever functions we want to simulate the game being played. Most
unit tests only focus on one single class but some (like testFruits) use the GameState class.
Exercise
- Familiarize yourself with the codebase by trying to find the files that contain the code mentioned in the slides