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Need help regarding how to draw smoothly in Java.


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#1 lthannyl   Members   -  Reputation: 103

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Posted 30 May 2012 - 05:39 PM

Hey guys, i've been making a little super mario clone in Java but I need help,

you see, if you download it and play it, you will notice it is quite stutter-y, and that really shouldn't be the case since it's such a small program.

So i assume it's 2 things, either my game loop is faulty (i'll provide the code below) or it's simply that Java just sucks at this, so I'm gonna go with the first one cause i love Java.


Anyways, here's my game loop.

		/**
	 * Contains the main flow of the game.
	 */
	private void run() {

		timer.schedule(new TimerTask() {
			private final BufferStrategy bf = frame.getBufferStrategy();
			private long startTime = System.currentTimeMillis();
			private long currTime = startTime;
			@Override
			public void run() {
				elapsedTime = System.currentTimeMillis() - currTime;
				currTime += elapsedTime;
				try {
					//get graphics
					g = bf.getDrawGraphics();
					//get input
					inputGame();
					//update the game
					updateGame(elapsedTime);
					//draw the game
					drawGame(g, elapsedTime);

				} finally {
					g.dispose();
				}

				// Shows the contents of the backbuffer on the screen.
				bf.show();

				Toolkit.getDefaultToolkit().sync();
			}
		//start this loop every 17 milliseconds, which is roughly 58 frames per second
		}, 10, 17);
	}

the variable timer, is of class Timer in Java.util.Timer, not the swing Timer, which i heard is unreliable, but this one is too clearly.

at the moment, I'm not really doing much with elapsedTime, but it's there just in case, i figured i didn't need it since that loop will
run every 17 milliseconds, and my update and rendering methods only take 2-5 milliseconds to finish.

Do you guys know of very effective game loops that provide very smooth rendering?

I can provide more code if necessary, Thanks in advance!

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#2 ChristerSwahn   Members   -  Reputation: 198

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Posted 31 May 2012 - 01:31 AM

Java2D (& Swing) can definitely handle simple animations smoothly, you need to work with it the right way though.

To begin with, all java graphics are normally rendered on its own AWT thread and you shouldn't do any painting on any other thread. (You can update game state etc on other threads but the data updates needs to be synchronized with the AWT thread.)

The painting is done by the paint() method of java.awt.Component and its subclasses/submethods. Usually you can simply create a subclass to JPanel, override the paintComponent() method and put your rendering in there (JPanel is double-buffered by default).

I'd recommend reading up on Swing a bit:
http://docs.oracle.com/javase/tutorial/uiswing/index.html

#3 The_Neverending_Loop   Members   -  Reputation: 596

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Posted 31 May 2012 - 10:07 AM

I've never had a problem with jittery ness, here are pieces of my code to show you what I do in java.

For one I create a class called widget that handle any kind of 2D art work I place on it and extends canvase

public class widget extends Canvas
{
	 private Renderable context = null;
    public void init()
    {
	    GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
	    GraphicsDevice gs = ge.getDefaultScreenDevice();
	    GraphicsConfiguration gc = gs.getDefaultConfiguration();
	    this.createBufferStrategy(2);
    }

    @Override public void paint(Graphics g)
    {
	    if(context != null)
		    g.drawImage(context.fullrender(), 0, 0, this);
	    else
	    {
		    g.setColor(Color.white);
		    g.fillRect(0, 0, this.getWidth(), this.getHeight());
	    }
    }
    public void updateContainer()
    {
	    BufferStrategy strat = this.getStrategy();
	    Graphics2D g2 = (Graphics2D)strat.getDrawGraphics();
	    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
	    g2.drawImage(context.fullrender(), 0, 0, null);
	    g2.dispose();
	    strat.show();
    }
   
    public void contentUpdate()
    {
	    this.validate();
	    this.repaint();
    }
}


and with each widget i give it a context, which implements another class I created called Renderable.

This Renderable class contains the actual information that needs to be drawn, so in its fullrender() method itll have all the sprites and tiles and where they need to be rendered to on the widget class, and the widget handles the double buffering and actual rendering to screen itself. That way i easily seperate the stuff I need to render from some of the logic I dont really need to see while setting up a scene to render.

#4 ChaoSXDemon   Members   -  Reputation: 96

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Posted 31 May 2012 - 12:52 PM

On top of my head I'm guessing it is because you are using TimerTask() class. I THINK (if I remembered correctly) if you don't have enough time that frame, TimerTask will NOT call it's run() method which means it won't "paint()" or "update()" or w/e method you stick inside TimerTask(). I suggest use a timer yourself by simply using "System.nanoTime()". This method returns a long that counts in nano seconds. So you should basically do this:

//...stuff from before
public void run(){
     startTime = System.nanoTime();
     update();
     render();
     endTime = System.nanoTime();
     long timediff = endTime - startTime;     //Find out the difference. This is in nano seconds
     startTime = endTime;     //So the next time, calculation can be done correctly
     sleepTime = (period - timeDiff);     //Period is how often you render/update your frame. 60 fps period = (1000.0/60) * 1000000L
                                                          //                                                                                                         this is ms     this is ms->ns
     try{
          Thread.sleep(sleepTime);
     }catch(InterrruptedException ex){}
}

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