Let’s Build a Simple Video Game with JRuby: A Tutorial

The article argues that JRuby lets Ruby use Java game libraries in a practical way, making it possible to build a simple game despite Ruby’s weaker game-development ecosystem. It introduces Slick and LWJGL, then walks through setup, a basic window, graphics, input handling, and a small bat-and-ball game.

Reading notes

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• JRuby is presented as a way to use Java libraries on the JVM from Ruby.
• Slick is described as a thin layer over LWJGL.
• LWJGL provides graphics, audio, controller input, and OpenCL.
• The setup uses RVM, Slick, and native libraries placed in the game directory.
• A basic JRuby game subclasses Slick’s BasicGame and defines render, init, and update.
• render draws the window contents, init loads resources, and update handles input and game changes.
• The sample game loads a background image, a ball image, and a paddle image.
• The paddle moves with the left and right arrow keys, using delta to scale movement.
• The ball moves with sine and cosine based on an angle value.
• Wall collisions change the ball angle.
• If the ball falls below the screen, the game resets the paddle, ball position, and angle.
• Paddle collision also changes the ball angle.
• The article says separate classes for paddle and ball would make the code cleaner.
• It mentions Slick’s StateBasedGame for games with menus, levels, and other states.
• It also mentions Warbler for packaging a Ruby app into a .jar file.
• Ludum Dare is cited as the motivation for exploring JRuby game development.