Space Invaders 104

Rendering in LWJGL

Introduction

• Initializing LWJGL
• Rendering sprites in LWJGL
• Keyboard input in LWJGL

This is going to a relatively short tutorial for several reasons. LWJGL is very simple to work with and has some strong similarities to JOGL and hence the last tutorial.

The final game can be see here. The complete source for the tutorial can be found here. Its intended that you read through this tutorial with the source code at your side. The tutorial isn't going to cover every line of code but should give you enough to fully understand how it works.

Context hightlighted source is also available here:

• LWJGLGameWindow.java
• LWJGLSprite.java
• TextureLoader.java
• Texture.java
• ResourceFactory.java

Disclaimer: This tutorial is provided as is. I don't guarantee that the provided source is perfect or that that it provides best practices.

LWJGL

This seems like a trivial point, especially when being illustrated by such a simplistic demo as this spaceinvaders game. However, LWJGL provides not just a graphics binding but a binding to OpenAL (an open standards sound system). In addition, LWJGL gives your access to input devices. This means your spaceinvaders game could be controlled from a gamepad and the aliens could squelch as they die, all from one library. Worth thinking about.

Adding a new rendering implementation for our SpaceInvaders game should be pretty simple (especially as in this case I didn't have to write the code, thanks Matzon). We're going to add 4 classes then plug then into our architecture.

LWJGL Window

Initialization

	Window.create(title, 100, 100, width, height, Display.getDepth(), 0, 8, 0, 0);

As you can see from the following code, OpenGL calls are simply prefixed with the class "GL11":

public void startRendering() {
	try {
		Window.create(title, 100, 100, width, height, Display.getDepth(), 0, 8, 0, 0);
      
		// grab the mouse, dont want that hideous cursor when we're playing!
		Mouse.setGrabbed(true);
 
		// enable textures since we're going to use these for our sprites
		GL11.glEnable(GL11.GL_TEXTURE_2D);
		
		// disable the OpenGL depth test since we're rendering 2D graphics
		GL11.glDisable(GL11.GL_DEPTH_TEST);
		
		GL11.glMatrixMode(GL11.GL_PROJECTION);
		GL11.glLoadIdentity();
		
		GL11.glOrtho(0, width, height, 0, -1, 1);
		
		textureLoader = new TextureLoader();
		
		if(callback != null) {
			callback.initialise();
		}
	} catch (LWJGLException le) {
		callback.windowClosed();
	}
   
	gameLoop();
}

Also note the line "Mouse.setGrabbed(true);". As we'll see later, the mouse and keyboard are also monitored from static contexts. This line simple says that the mouse cursor shouldn't be displayed in the window.

Game Loop

private void gameLoop() {
	while (gameRunning) {
		// clear screen
		GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);
		GL11.glMatrixMode(GL11.GL_MODELVIEW);
		GL11.glLoadIdentity();
			
		// let subsystem paint
		if (callback != null) {
			callback.frameRendering();
		}
			
		// update window contents
		Window.update();
			
		if(Window.isCloseRequested() || Keyboard.isKeyDown(Keyboard.KEY_ESCAPE)) {
			gameRunning = false;
			Window.destroy();
			callback.windowClosed();
		}
	}
}

Keyboard Handling

public boolean isKeyPressed(int keyCode) {
	// apparently, someone at decided not to use standard 
	// keycode, so we have to map them over:
	switch(keyCode) {
	case KeyEvent.VK_SPACE:
		keyCode = Keyboard.KEY_SPACE;
		break;
	case KeyEvent.VK_LEFT:
		keyCode = Keyboard.KEY_LEFT;
		break;
	case KeyEvent.VK_RIGHT:
		keyCode = Keyboard.KEY_RIGHT;
		break;
	}    
	
	return Keyboard.isKeyDown(keyCode);
}

LWJGL Sprite

public void draw(int x, int y) {
	// store the current model matrix
	GL11.glPushMatrix();
		
	// bind to the appropriate texture for this sprite
	texture.bind();
    
	// translate to the right location and prepare to draw
	GL11.glTranslatef(x, y, 0);		
    	GL11.glColor3f(1,1,1);
		
	// draw a quad textured to match the sprite
    	GL11.glBegin(GL11.GL_QUADS);
	{
	      GL11.glTexCoord2f(0, 0);
	      GL11.glVertex2f(0, 0);
	      GL11.glTexCoord2f(0, texture.getHeight());
	      GL11.glVertex2f(0, height);
	      GL11.glTexCoord2f(texture.getWidth(), texture.getHeight());
	      GL11.glVertex2f(width,height);
	      GL11.glTexCoord2f(texture.getWidth(), 0);
	      GL11.glVertex2f(width,0);
	}
	GL11.glEnd();
		
	// restore the model view matrix to prevent contamination
	GL11.glPopMatrix();
}

Textures

Plugging it Together - ResourceFactory updates

public GameWindow getGameWindow() {
	// if we've yet to create the game window, create the appropriate one
	// now
	if (window == null) {
		switch (renderingType) {
			case JAVA2D:
			{
				window = new Java2DGameWindow();
				break;
 			}
			case OPENGL_JOGL:
			{
				window = new JoglGameWindow();
				break;
			}
			case OPENGL_LWJGL:
			{
				window = new LWJGLGameWindow();
				break;
			}
		}
	}

	return window;
}

public Sprite getSprite(String ref) {
	if (window == null) {
		throw new RuntimeException("Attempt to retrieve sprite before game window was created");
	}
		
	switch (renderingType) {
		case JAVA2D:
		{
			return Java2DSpriteStore.get().getSprite((Java2DGameWindow) window,ref);
		}
		case OPENGL_JOGL:
		{
			return new JoglSprite((JoglGameWindow) window,ref);
		}
		case OPENGL_LWJGL:
		{
			return new LWJGLSprite((LWJGLGameWindow) window,ref);
		}
	}
		
	throw new RuntimeException("Unknown rendering type: "+renderingType);
}

Exercises for the Reader

Add sound effects using LWJGL

Add controller support using LWJGL

Support Fullscreen mode in LWJGL

Further Reading