Appendix A: Config Files

In the full Pong example, the paddle sizes, ball sizes, colors, and arena size are all hard-coded into the implementation. This means that if you want to change any of these, you need to recompile the project. Wouldn't it be nice to not have to recompile the project each time you wanted to change one or all of these things?

Luckily, Amethyst uses RON configuration files and has infrastructure in the form of the Config trait to help us implement our own config files.

Structure of the Config File

The existing example uses the following constants:

const ARENA_HEIGHT: f32 = 100.0;
const ARENA_WIDTH: f32 = 100.0;
const PADDLE_HEIGHT: f32 = 15.0;
const PADDLE_WIDTH: f32 = 2.5;
const PADDLE_VELOCITY: f32 = 75.0;
const PADDLE_COLOR: [f32; 4] = [0.0, 0.0, 1.0, 1.0];

const BALL_VELOCITY_X: f32 = 75.0;
const BALL_VELOCITY_Y: f32 = 50.0;
const BALL_RADIUS: f32 = 2.5;
const BALL_COLOR: [f32; 4] = [1.0, 0.0, 0.0, 1.0];

to specify the look of the game. We want to replace this with something more flexible in the form of a config file. To start, let's create a new file,, to hold our configuration structures. Add the following use statements to the top of this file:

use std::path::Path;

use amethyst::config::Config;

For this project, we'll be placing a config.ron file in the same location as the display.ron and input.ron files (likely the config/ folder).