[ssjwizard]

Java programming with OpenGL #1 - Introduction

Welcome to the first installment of my Java programming tutorial series. I will begin from the position that you have some basic understanding of programming. I'd like to introduce you to my latest project: building a game engine using the highly portable Java for logic handling. As many of you already know, Java graphics rendering is horrifically slow and bulky on system resources. Now for any of us here at OCF this really isn't an issue as our machines are very capable; However, as an independent developer in today's market portability and uniqueness reign supreme. So I have selected OpenGL as a candidate to replace Java's graphics rendering.

To access OpenGL through Java we will be working with LWJGL. You may know a bit about LWJGL, and may also know that Slick 2D is a game library built on top of LWJGL, so why not start there? If all we wanted to do was produce a simple game then that would be fine, but we're here to learn the fundamentals of building a game library.

Ok for our projects we will be needing a few tools:

1. Java SE 1.6 Developers Kit or higher found HERE
2. Eclipse for Java Developers found HERE.
3. LWJGL found HERE.

Installing LWJGL

LWJGL is a library and isn't "installed" but rather needs to be included in our project. Detailed instructions can be found HERE.

I recommend placing the LWJGL .jar files Slick_Util.jar and the appropriate natives for your OS(I use the Windows natives but will include the OSX and Linux natives in my finished game) into a folder inside your eclipse workspace before creating any projects.

You should begin by opening eclipse and creating a new Project.



Select new Java Project.



Enter a project name and select a developer environment. For compatibility reasons I will be using JavaSE 1.6.



Now right click on your project and select properties.



Select Java Build Path, click the libraries tab, and the click Add External JARs.



Navigate to the folder where you put the LWJGL .jar files. Select all 3 files and click Open.



Expand the lwjgl.jar options and select Native library location, and then click Edit.



Click on External Folder, and navigate to the folder where you put LWJGL then select the natives folder and click Ok.



Click OK to close the properties window. Now expand your project folder in the explorer, right click on the src folder and create a new Class.



Enter a name for your class I will use HelloWorld, and then check the box for public static void main..



Now open up your new class into the Java editor. We are going to need a few imports to get started and they are:

Code:

import static org.lwjgl.opengl.GL11.*;
import org.lwjgl.opengl.*;
import org.lwjgl.*;

Now as java is an Object oriented language were going to want to get out of the static main method ASAP to do this we will simply call the constructor of the class.

Code:

public static void main(String[] args) {
  new HelloWorld();
}

All were going to do with this example now is create a basic window which we can draw content onto later. We're going to be calling a few of LWJGL Display's methods to do this:

1. Display.setDisplayMode
2. Display.setTitle
3. Display.create

The LWJGL library throws a LWJGLException so these calls must be nested within a try catch block.

Code:

try {
  Display.setDisplayMode(new DisplayMode(800,500));
  Display.setTitle("Hello from LWJGL!");
  Display.create();
} 
 catch (LWJGLException e) {
    e.printStackTrace();
 }

We have the display now, but it isn't rendering yet. The next step is create a simple display loop. For this, we will use a while statement attached to the Display.isCloseRequested method. To force a draw to the screen, we will need to use the Display.update method. Next we will limit the games system resources by assigning a frame rate cap using the Display.sync method.

Code:

    //program starts here
  while(!Display.isCloseRequested()){
    Display.update();
    Display.sync(60);
  }

Finally we will call the Display.destroy method to close the window once display requests to be closed

Code:

Display.destroy();

Bringing it all together

Code:

import static org.lwjgl.opengl.GL11.*;
import org.lwjgl.opengl.*;
import org.lwjgl.*;

public class HelloWorld {

  public static void main(String[] args) {
    new HelloWorld();
  }

  public HelloWorld(){
    try {
      Display.setDisplayMode(new DisplayMode(800,500));
      Display.setTitle("Hello from LWJGL!");
      Display.create();
      
    } 
    catch (LWJGLException e) {
      e.printStackTrace();
    }
    
      //program starts here
    while(!Display.isCloseRequested()){
      Display.update();
      Display.sync(60);
    }
    
    Display.destroy();
  }

}

That's pretty much it for this installment. We have setup eclipse, started a project, linked to our OpenGL library, and created a Display. We are now ready to start coding our game engine. I look forward to bringing the second installment of this series on basic shapes and colors!

[Badbonji]

This looks great, been planning on learning some Java alongside practicing C++ this summer whilst I am free from uni.

[ssjwizard]

Thought Id point out I posted a Snake game that I developed my framework that we will be going through with these articles over in the GAMES forum.

[dropadrop]

Great idea, I'm looking forward to this.

[ssjwizard]

Second issue has been posted HERE