CODEWITHSUNDEEP
javagraphicsrepaintflicker
user2627736
user2627736

Reputation: 301

Java - Flicker when using repaint()

Hello I i'm having random flicker every couple of seconds when running my program, it has a single image moving across screen. I'm using Graphics paint() method and repaint() in the thread's run() method. Here are the relevant parts of the code, i'll post entire code if necessary. Btw, pawns is an arraylist loaded with pawn objects, originally I had 5 threads for 5 images moving across but I tried with only 1 image and it still flickers so it's not that.

private BufferedImage helicopter;

helicopter = ImageIO.read(new File("white.png"));

public void paint(Graphics g) {
      g.setColor(Color.WHITE);
      g.fillRect(0, 0, this.getWidth(), this.getHeight());
      for(count=0; count<pawns.size(); count++){
         g.drawImage(helicopter, pawns.get(count).getX(), pawns.get(count).getY(), null);
      }
      g.setColor(Color.BLACK);
      g.drawLine(350, 0, 350, 600);
   }

public void run() {
         while(true) {
            randSleep = (int)(Math.random()*100);
            randMove = (int)(Math.random()*2);
            pawn.setX(pawn.getX()+randMove);
            try{
               Thread.sleep(40);
            } 
            catch(Exception e) {
               e.printStackTrace();
            }

            repaint();

         }
      }

Upvotes: 1

Views: 2246

Answers (1)

gnate
gnate

Reputation: 68

On components with complex output, repaint() should be invoked with arguments which define only the rectangle that needs updating, rather than the no-arg version, which causes the entire component to be repainted.

Swing's implementation of paint() factors the call into 3 separate callbacks: paintComponent() paintBorder() paintChildren() Extensions of Swing components which wish to implement their own paint code should place this code within the scope of the paintComponent() method ( not within paint()).

source: Painting in AWT and Swing: Good Painting Code Is the Key to App Performance

You should notice in the source quoted and linked that repaint() (no arguments) will call update(), which by default clears the background before drawing. I suspect that this is the source of the flicker, when the component is cleared before calling paint().

If you are using Swing components you should not implement your own double buffering but instead use the functionality provided by Swing.

First try, calling a repaint with arguments to avoid update clearing the entire background. Or write an override for the update method. If that does not solve the problem next try putting your drawing code in the paintComponent method of a Swing component.

Upvotes: 2

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