How optimize paintComponent?

[joan wo]

Hello,

I'm developing an application that draw a shape over an image and then after clic a button, the application calculate all the points that are into the shape and paint it with the same color as the shape.
I paint the shape in the paintComponent method. My problem is that performance of the application descends dramatically in the moment that have to repaint all this points. How can I increase the performance?

I have the rectangle that includes the shape and I use a byte[] to store the points (1 are into the shape, 0 are out).

Thank's a lot.

[Craig Wood]

Try using the shape to set the clip for the graphics context and then draw the image.

protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.setClip(shape);
    g.drawImage(image, ...

The image pixels that fall inside the clipping shape should be the only ones rendered.

[Ilja Preuss]

And for painting the image in a different color, take a look at the class RGBImageFilter.

[joan wo]

Hello,

Thank's a lot for your replies.

I have two doubts:
- In the shape I only have the points of the border of the shape. I have to find all the points of the interior of the shape, is in this process when the process is too slow. How can I use the setClip method to obtain the points of the interior?
- Is possible to call paintComponent (with reapint) only when there are a change on the image. I've tried to do it, but then the shape is not ever repaint it, and disappears.

Thank's.

[Craig Wood]

import java.awt.*;
import java.awt.geom.*;
import java.awt.image.*;
import java.io.*;
import javax.imageio.ImageIO;
import javax.swing.*;
 
public class Clipping extends JPanel {
    BufferedImage[] images;
    int index;
    Shape clip = new Ellipse2D.Double(160,50,100,100);
 
    Clipping(BufferedImage[] images) {
        this.images = images;
    }
 
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        int x = (getWidth() - images[index].getWidth())/2;
        int y = 40;
        g2.drawImage(images[index], x, y, this);
        g2.setPaint(Color.red);
        g2.draw(clip);
        // Move down to demonstrate the clipping affect.
        AffineTransform at = AffineTransform.getTranslateInstance(0,200);
        // Clip image.
        g2.setClip(at.createTransformedShape(clip));
        // To filter image so we can show it in new location.
        BufferedImageOp op = new AffineTransformOp(at,
                                     AffineTransformOp.TYPE_BICUBIC);
        g2.drawImage(images[index], op, x, y);
        // Smooth edge of clip.
        g2.setPaint(getBackground());
        g2.draw(at.createTransformedShape(clip));
    }
 
    private void start() {
        Thread thread = new Thread(new Runnable() {
            public void run() {
                long delay = 4000;
                boolean animate = true;
                while(animate) {
                    try {
                        Thread.sleep(delay);
                    } catch(InterruptedException e) {
                        animate = false;
                        break;
                    }
                    index = (index+1 > images.length-1) ? 0 : index+1;
                    repaint();
                }
            }
        });
        thread.setPriority(Thread.NORM_PRIORITY);
        thread.start();
    }
 
    public static void main(String[] args) throws IOException {
        String[] ids = {      // approx size = 300, 200
            "greathornedowl", "bclynx", "redfox", "mtngoat"
        };
        BufferedImage[] images = new BufferedImage[ids.length];
        for(int j = 0; j < images.length; j++) {
            String path = "images/" + ids[j] + ".jpg";
            images[j] = ImageIO.read(new File(path));
        }
        Clipping test = new Clipping(images);
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(test);
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
        test.start();
    }
}