How to deal with SwingWorker thread that goes slow?

Question

Hardly, do I understand multithreading stuff. And beginning look into it , I faced one issue, that came in my mind. I have recently wrote one simple application, and as soon as I get some new knowledge about Java I wish to improve my app with that I’ve learned. It looks like simple swing GUI that updates images every period of time. I implemented ActionListener and overrode actionPerformed method. Timer with 15ms delay, repainted JPanelclass and everything worked fine. But I thought that updating my GUI using timer directly in actionPerformed (I presume that it’s another thread, but I’m barely sure) is bad idea. So I decided to change code and use SwingWorker. I called all my methods for my animation inside process() .. and again app working fine but it became extremely slow. Now I’m thinking what’s wrong? Why it acts slower then before ? My timer delay is actually not waiting 15ms , it’s much slower even though delay the same. Am I made mistake with multithreading ? Help me understand this stuff. Thanks in advance

public class GameEngine() extends SwingWorker<Void, Drawable>
GamePanel gp; // ref to JPanel class
{
 public GameEngine(GamePanel gp)
 {
  this.gp = gp;
 }
}
protected void doInBackground()
{
 publish();
}
protected void process(List<Drawable> chunks)
{
 Timer timer = new Timer(15, e ->
 {
  //methods for animation 
  fall();
  animate();
  checkTouch();
 });
}

Some code I left beyond. If you need it I can write...

EDITION

Just for clarity of my issue I provide some more examples and addition explanation.

**Used to be: **

public class GamePanel extends JPanel
{
 public void GamePanel()
 {
 GameEngine engine = new GameEngine(this);
 }
 //some images , variables etc...
  protected void paintComponent(Graphics g)
  super.paintComponent(g)
  g.drawImage(image1, x, y, null);
  g.drawImage(image2, w, z,null);
 ...
}
public class GameEngine () implements ActionListener
{
 GamePanel gp;
 Timer timer;
 public void GameEngine(GamePanel gp)
 {
  this.gp = gp;
  timer = new Timer( 15 , this );
 }
 public void actionPerformed()
 {
  //these methods repaint my GamePanel every 15ms.
  fall(); // make object (image) increment on Y Axis 
  animate(); // make another object (image) decrement on X Axis
  checkTouch(); // check if objects collided
 }
}

**Became: **

public class GamePanel extends JPanel
{
 public void GamePanel()
 {
 GameEngine engine = new GameEngine(this);
 }
 //some images , variables etc...
  protected void paintComponent(Graphics g)
  super.paintComponent(g)
  g.drawImage(image1, x, y, null);
  g.drawImage(image2, w, z,null);
 ...
}
public class GameEngine () extends SwingWorker<Void, Drawable>
{
 GamePanel gp;
 Timer timer;
 public void GameEngine(GamePanel gp)
 {
  this.gp = gp;
 }
 protected void doInBackground()
 {
  process();
 }
 protected void progress()
 {
  timer = new Timer (15, e-> 
  {
   new ActionListener(new actionPerformed)
   {
      //these methods repaint my GamePanel every 15ms.
  fall(); // make object (image) increment on Y Axis 
  animate(); // make another object (image) decrement on X Axis
  checkTouch(); // check if objects collided
   }
  });
 }
 protected void done()
 {
 };
}

When I created it first I implemented ActionListener and updated my panel through timer declared in constructor.. I presumed that it’s thread-unsafe. That’s why I transfer everything in progress method where I declared timer which ActionListener as lambda argument. In other words I call all methods for animation in another thread. Finally it became slower, comparing with first example.. I don’t understand

1. Is Timer from first example EDT or it’s another thread ?
2. My first example is thread safe ?
3. Why my second example goes much slower then first one ?

I heard about NOT update your GUI outside EDT, is it that case?

Answer 1

There is not enough information in your question to answer it, but I will take your queries about multi-threading and the implied question about Swing and rendering and see if I can help you out.

I think the most likely reason for your slowdown is unnecessary screen updating. Once a pixel has been drawn onto the canvas or whatever in your application, usually your application does not need to redraw it unless it is supposed to change; either a sprite moves or some other image in your app obscures a part of the drawing temporarily and then needs to be restored.

It is common for a novice repainting to ignore this, and just repaintng the entire painted surface. Although this will work, it is slow; if you're doing it a number of times in a loop, then the loop will seem slow.

The better way to do this is to use the rectangle passed into the redrawing routine and only repaint its intersection with the entire surface redrawn by your routine -- this cuts way down on the part that needs to be redrawn, and therefore on the time it takes to redraw it.

As for multithreading, I think it's helpful to think of it the way we used to think of things in a single-processor world -- the computer does something for a while, then stops in a place you cannot predict and does something in the other thread for a while, etc. You cannot assume the order in which things are going to get done, or how long it will spend on each thing, etc.

With modern multi-core computers, it is possible that these things in fact get done at the same time, but I don't know that trying to envision that helps you any.