pacman/exercises/13/navigate_codebase/README.md

[< Back](../README.md)

# 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

1. Familiarize yourself with the codebase by trying to find the files that contain the code mentioned in the slides