- Ludum Dare 47
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Commedia dell'Arte: Masks, masters and servants. Commedia dell'Arte is a humorous graphic adventure experience (10min) for PC Windows, Mac OS X and Linux about theater and improvisation. Ludum Dare 34 Results. See the winners! Real World Gatherings. But I couldn't figure out at all which path I was supposed to take and ended up getting stuck:Mac OS 10.10. Apr 29, 2013 Ludum Dare 26: 48-hour Game Design Compo. This weekend, I decided to participate in a 48-hour game design “competition”. Ludum Dare is a compo that asks you to create a video game from scratch in a 48-hour time period – you have to write your code and create all of your assets in that time period. . Includes an automatic modification of the `java.library.path` system property which.adds. the path `lib/natives-.system.` to the path, where.system. is one of `linux`, `windows`, `mac` or `solaris`. Includes a basic class `MyGame` ready to be filled with the game implementation. Includes an HTML file with an applet ready to be used. Fragments of Euclid is a game about exploring and solving puzzle in a mind-bending environment inspired by M.C. Escher.Enjoy the peaceful mood while trying to.
Let’s Build a Simple Video Game with JRuby: A Tutorial
Ruby isn't known for its game development chops despite having a handfulofinterestinglibraries suited to it. Java, on the other hand, has a thriving and popular game development scene flooded with powerful libraries, tutorials and forums. Can we drag some of Java's thunder kicking and screaming over to the world of Ruby? Yep! - thanks to JRuby. Let's run through the steps to build a simple 'bat and ball' game now.
The Technologies We'll Be Using
Ludum Dare 47
JRuby
If you're part of the 'meh, JRuby' brigade, suspend your disbelief for a minute. JRuby is easy to install, easy to use, and isn't going to trample all over your system or suck up all your memory. It will be OK!
One of JRuby's killer features is its ability to use Java libraries and generally dwell as a first class citizen on the JVM. JRuby lets us use performant Java powered game development libraries in a Rubyesque way, lean on Java-based tutorials, and basically have our cake and eat it too.
To install JRuby, I recommend RVM (Ruby Version Manager). I think the JRuby core team prefer you to use their own installer but
rvm install jruby
has always proven quick and effective for me. Once you get it installed, rvm use jruby
and you're done.Slick and LWJGL
The Slick library is a thin layer of structural classes over the top of LWJGL (Lightweight Java Game Library), a mature and popular library that abstracts away most of the boring system level work.
Out of the box LWJGL gives us OpenGL for graphics, OpenAL for audio, controller inputs, and even OpenCL if we wanted to do heavy parallelism or throw work out to the GPU. Moon way mac os. Slick gives us constructs like game states, geometry, particle effects, and SVG integration, while allowing us to drop down to using LWJGL for anything we like.
Getting Started: Installing Slick and LWJGL
Rather than waste precious time on theory, let's get down to the nitty gritty of getting a basic window and some graphics on screen:
- First, create a folder in which to store your game and its associated files. From here I'll assume it's
/mygame
- Go to the Slick homepage and choose 'Download Full Distribution' (direct link to .zip here).
- Unzip the download and copy the
lib
folder into your/mygame
as/mygame/lib
- this folder includes both LWGWL and Slick. - In
/mygame/lib
, we need to unpack thenatives-[your os].jar
file and move its contents directly into/mygame
.Mac OS X: Right click on thenatives-mac.jar
file and select to unarchive it (if you have a problem, grab the awesome free The Unarchiver from the App Store) then drag the files in/mygame/lib/native-mac/*
directly into/mygame
.Linux and Windows: Runningjar -xf natives-linux.jar
orjar -xf natives-win32.jar
and copying the extracted files back to/mygame
should do the trick. - Now your project folder should look a little like this:If so, we're ready to code.
![Lost path (ludum dare 45) mac os download Lost path (ludum dare 45) mac os download](https://img.itch.zone/aW1nLzI1NjM5ODcucG5n/original/8xSyvK.png)
A Bare Bones Example
Leaping in with a bare bones example, create
/mygame/verybasic.rb
and include this code:Ensure that
ruby
actually runs JRuby (using ruby -v
) and then run it from the command line with ruby verybasic.rb
. Assuming all goes well, you'll see this:If you don't see something like the above, feel free to comment here, but your problems most likely orient around not having the right 'native' libraries in the current directory or from not running the game in its own directory in the first place (if you get
probable missing dependency: no lwjgl in java.library.path
- bingo).Explanation of the demo code
$:.push File.expand_path('./lib', __FILE__)
pushes the 'lib' folder onto the load path. (I've usedpush
because my preferred << approach breaks WordPress ;-))require 'java'
enables a lot of JRuby's Java integration functionality.- Note that we can use
require
to load the .jar files from the lib directory. - The
java_import
lines bring the named classes into play. It's a little likeinclude
, but not quite. - We lean on Slick's
BasicGame
class by subclassing it and adding our own functionality. render
is called frequently by the underlying game engine. All activities relevant to rendering the game window go here.init
is called when a game is started.update
is called frequently by the underlying game engine. Activities related to updating game data or processing input can go here.- The code at the end of the file creates a new
AppGameContainer
which in turn is given an instance of our game. We set the resolution to 640x480, ensure it's not in full screen mode, and start the game.
Fleshing Out a Bat and Ball Game
The demo above is something but there are no graphics or a game mechanic, so it's far from being a 'video game.' Let's flesh it out to include some images and a simple pong-style bat and ball mechanic.
Note: I'm going to ignore most structural and object oriented concerns to flesh out this basic prototype. The aim is to get a game running and to understand how to use some of Slick and LWJGL's features. We can do it again properly later :-)
All of the assets and code files demonstrated here are also available in an archive if you get stuck. Doing it all by hand to start with will definitely help though.
A New Code File
Start a new game file called
pong.rb
and start off with this new bootstrap code (very much like the demo above but with some key tweaks):Make sure it runs, then move on to fleshing it out.
A Background Image
It'd be nice for our game to have an elegant background. I've created one called
bg.png
which you can drag or copy and paste from here (so it becomes /mygame/bg.png
):Now we want to load the background image when the game starts and render it constantly.
To load the game at game start, update the
init
and render
methods like so:The
@bg
instance variable picks up an image and then we issue its draw
method to draw it on to the window every time the game engine demands that the game render itself. Run pong.rb
and check it out.Adding A Ball and Paddle
Adding a ball and paddle is similar to doing the background. So let's give it a go:
The graphics for
ball.png
and paddle.png
are here. Place them directly in /mygame
.We now have this:
Note: As I said previously, we're ignoring good OO practices and structural concerns here but in the long run having separate classes for paddles and balls would be useful since we could encapsulate the position information and sprites all together. For now, we'll 'rough it' for speed.
Making the Paddle Move
Making the paddle move is pretty easy. We already have an input handler in
update
dealing with the Escape key. Let's extend it to allowing use of the arrow keys to update @paddle_x
too:It's crude but it works! (P.S. I'd normally use
&&
instead of and
but WordPress is being a bastard - I swear I'm switching one day.)If the left arrow key is detected and the paddle isn't off the left hand side of the screen,
@paddle_x
is reduced by 0.3 * delta
and vice versa for the right arrow.The reason for using
delta
is because we don't know how often update
is being called. delta
contains the number of milliseconds since update
was last called so we can use it to 'weight' the changes we make. In this case I want to limit the paddle to moving at 300 pixels per second and 0.3 * 1000 (1000ms = 1s) 300.Making the Ball Move
Making the ball move is similar to the paddle but we'll be basing the
@ball_x
and @ball_y
changes on @ball_angle
using a little basic trigonometry.If you stretch your mind back to high school, you might recall that we can use sines and cosines to work out the offset of a point at a certain angle within a unit circle. For example, our ball is currently moving at an angle of
45
, so:Note: The
* Math::PI / 180
is to convert degrees into radians.We can use these figures as deltas by which to move our ball based upon a chosen ball speed and the
delta
time variable that Slick gives us.Add this code to the end of
update
:If you run the game now, the ball will move up and right at an angle of 45 degrees, though it will continue past the game edge and never return. We have more logic to do!
Note: We use
-=
with @ball_y
because sines and cosines use regular cartesian coordinates where the y axis goes from bottom to top, not top to bottom as screen coordinates do.Add some more code to
update
to deal with ball reflections:This code is butt ugly and pretty naive (get ready for a nice OO design assignment later) but it'll do the trick for now. Run the game again and you'll notice the ball hop through a couple of bounces off of the walls and then off of the bottom of the screen.
Resetting the Game on Failure
When the ball flies off of the bottom of the screen, we want the game to restart. Let's add this to
update
:It's pretty naive again, but does the trick. Ideally, we would have a method specifically designed to reset the game environment, but our game is so simple that we'll stick to the basics.
Paddle and Ball Action
We want our paddle to hit the ball! All we need to do is cram another check into
update
(poor method - promise to refactor it later!) to get things going:Note: WordPress has borked the less than operator in the code above. Eugh. Fix that by hand ;-)
And bingo, we have it. Run the game and give it a go. We have a simple, but performant, video game running on JRuby.
![Path Path](https://preview.redd.it/65ikzgyps2r31.png?width=1924&format=png&auto=webp&s=1bc1abd71d857b32e5d56cad6b867fe9e8f267e5)
If you'd prefer everything packaged up and ready to go, grab this archive file of my /mygame directory.
What Next?
Object orientation
As I've taken pains to note throughout this article, the techniques outlined above for maintaining the ball and paddle are naive - an almost C-esque approach.
Building separate classes to maintain the sprite, position, and the logic associated with them (such as bouncing) will clean up the
update
method significantly. I leave this as a task for you, dear reader!Stateful Games
Games typically have multiple states, including menus, game play, levels, high score screens, and so forth. Slick includes a
StateBasedGame
class to help with this, although you could rig up your own on top of BasicGame
if you really wanted to.The Slick wiki has some great tutorials that go through various elements of the library, including a Tetris clone that uses game states. The tutorials are written in Java, naturally, but the API calls and method names are all directly transferrable (I'll be writing an article about 'reading' Java code for porting to Ruby soon).
Packaging for Distribtion
One of the main reasons I chose JRuby over the Ruby alternatives was the ability to package up games easily in a .jar file for distribution. The Ludum Dare contest involves having other participants judge your game and since most participants are probably not running Ruby, I wanted it to be relatively easy for them to run my game.
Lost Path (ludum Dare 45) Mac Os Update
Warbler is a handy tool that can produce .jar files from a Ruby app. I've only done basic experiments so far but will be writing up an article once I have it all nailed.
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Ludum Dare
Lost Path (ludum Dare 45) Mac Os Download
Our roost mac os. I was inspired to start looking into JRuby and Java game libraries by the Ludum Dare game development contest. They take place every few months and you get 48 hours to build your own game from scratch. I'm hoping to enter for the first time in just a couple of days and would love to see more Rubyists taking part.