Thread: How to detect mouse event while painting in a loop

That's an interesting problem. I would perhaps use a BufferedImage, and draw one shape at a time to it (in a synchronized block), then call repaint() after each shape is drawn to the image. In paintComponent(), draw the image in another block, synchronized to the same thing as the drawing to the image is. That way you aren't constantly tying up the EDT, which will hopefully give you a chance to catch the events. I'm really not sure though. If you provide an SSCCE, perhaps we can experiment with it.

Hmm. I'd be interested in seeing an SSCCE that I could play with. This is an interesting problem.

Originally Posted by KevinWorkman

Hmm. I'd be interested in seeing an SSCCE that I could play with. This is an interesting problem.

OK. In the following code, the mouseMoved() method resets the line count to zero. When this happens (when the mouse moves), I want the painting of lines to restart from the beginning immediately. Obviously, this doesn't happen if you run the code, may be because repaint() is asynchronous.. As you can see, I also tried to call paintComponent() directly, to draw the image from the loop, or call update() without achieving the desired effect which is -- once again: erase the panel background with the black pen and redraw in white from the 1st line IMMEDIATELY as soon as the mouse moves.

I really appreciate your help. Thanks.

Robert

PS. Please copy/paste in Eclipse, select all and reformat using ctrl+shift+F / no idea with other editors. The java file should be named SyncPaint.java. For some reason, the EXIT_ON_CLOSE token is not posted correctly below, please edit the token manually, sorry. BTW, do you know a link explaining how to post code correctly here please??

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Insets;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Line2D;
import java.awt.image.BufferedImage;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
 
@SuppressWarnings("serial")
class SyncPaintPanel extends JPanel {
 
    private BufferedImage paintImage = null;
    private Line2D[] linesArray;
    private int lineCount;
 
    SyncPaintPanel(JFrame frame, int width, int height) {
 
        int w, h;
 
        Insets insets = frame.getInsets();
 
        w = frame.getWidth() - insets.left - insets.right;
        h = frame.getHeight() - insets.top - insets.bottom;
 
        setSize(w, h);
 
        linesArray = new Line2D[h];
 
        for (int i = 0; i < h; i++) {
            linesArray[i] = new Line2D.Double(i*w/h, i, w - i*w/h - 1, i);
        }
 
        addMouseMotionListener(new SyncMouseListener());
    }
 
    void refresh() {
 
        if (paintImage == null) {
            paintImage = (BufferedImage) createImage(getWidth(), getHeight());
        }
 
        Graphics2D g2d = paintImage.createGraphics();
 
        lineCount = 0;
 
        while(lineCount < getHeight()) {
 
            if(lineCount == 0) {
 
                g2d.setColor(Color.black);
                g2d.fillRect(0, 0, getWidth(), getHeight());
 
                //paintComponent(getGraphics());
                //getGraphics().drawImage(paintImage, 0, 0, this);
                //update(getGraphics());
                repaint(0);
 
                g2d.setColor(Color.white);
            }
 
            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
 
            g2d.draw(linesArray[lineCount++]);
            repaint(0);
        }
 
        g2d.dispose();
 
    }
 
    public void paintComponent(Graphics g) {
 
        if (paintImage != null) {
            g.drawImage(paintImage, 0, 0, this);
        }
 
    }
 
    class SyncMouseListener extends MouseAdapter {
 
        public void mouseMoved(MouseEvent e) {
            //System.out.println("mouse move");
            lineCount = 0;
        }
 
    }
 
}
 
public class SyncPaint {
 
    public static void main(String[] args) {
 
        JFrame frame = new JFrame("SyncPaint");
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(null);
        frame.setSize(400, 600);
        SyncPaintPanel panel = new SyncPaintPanel(frame, frame.getWidth(),
                frame.getHeight());
        frame.add(panel);
 
        panel.refresh();
    }
 
}

I don't normally do this, but I've modified your code to show you one way to accomplish your goal. The solution is relatively simple, but let me know if anything doesn't make sense.

I also edited your post to include the highlight tags.

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Line2D;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
 
@SuppressWarnings("serial")
class SyncPaintPanel extends JPanel {
 
	private Line2D[] linesArray;
 
	private int linesToDraw = 0;
 
	Timer timer = new Timer(10, new ActionListener(){
		public void actionPerformed(ActionEvent e){
			if(linesToDraw < linesArray.length){
				linesToDraw++;
			}
			else{
				timer.stop();
			}
			repaint();
		}
	});
 
	SyncPaintPanel(JFrame frame, int width, int height) {
 
		int w, h;
 
		Insets insets = frame.getInsets();
 
		w = frame.getWidth() - insets.left - insets.right;
		h = frame.getHeight() - insets.top - insets.bottom;
 
		setSize(w, h);
 
		linesArray = new Line2D[h];
 
		for (int i = 0; i < h; i++) {
			linesArray[i] = new Line2D.Double(i*w/h, i, w - i*w/h - 1, i);
		}
 
		addMouseMotionListener(new SyncMouseListener());
 
		timer.start();
	}
 
	public void paintComponent(Graphics g) {
 
		super.paintComponent(g);
 
		for(int lineCount = 0; lineCount < linesToDraw; lineCount++) {
			((Graphics2D)g).draw(linesArray[lineCount]);			
		}
	}
 
	class SyncMouseListener extends MouseAdapter {
 
		public void mouseMoved(MouseEvent e) {
			linesToDraw = 0;
			timer.start();
		}
	}
}
 
public class SyncPaint {
 
	public static void main(String[] args) {
 
		JFrame frame = new JFrame("SyncPaint");
		frame.setVisible(true);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setLayout(null);
		frame.setSize(400, 600);
		SyncPaintPanel panel = new SyncPaintPanel(frame, frame.getWidth(),
				frame.getHeight());
		frame.add(panel);
 
	}
 
}