How to delete shapes drawn on an Image

Question

I am developing a small Paint tool. And I am able to load and draw Lines or Circles and other shapes on an image. Also I have an eraser tool to erase the shapes that I have drawn.
This is code for that:

g.setColor(getColor().WHITE);
g.fillRect(getXAxis() - getThickness(), getYAxis() - getThickness(), getThickness() * 2, getThickness() * 2);

My problem is that, If I have loaded an image and drawn some shapes on it. Then when I tried to erase the shapes, the image is also gets replaced with white color.
Is there any way to set the image as the background while using fillRect() to erase the shape, so that my image will be untouched.

I think you want to call g.drawImage(XXX) before doing anything else on your graphics 2d — iXô, Jun 14 '16 at 09:46
You need 2 images drawn one over another. First is your source image. Second is the image with your lines/shapes. If you want to erase something, you need to fill rect on your second image with a trasparent color. — Sergiy Medvynskyy, Jun 14 '16 at 09:59
you use drawImage, then draw a circle, then try to remove that circle ? all on the same graphics2d instance ? if so, it is normal that the background is deleted. — iXô, Jun 14 '16 at 10:00
Is this `g` the `Graphics` that you receive in `paintComponent`, or the `Graphics` that you obtained from a `BufferedImage`? — Marco13, Jun 14 '16 at 10:36
Then the image itself is totally unaffected by these lines. If you want to "erase" them, simply omit the corresponding `drawLine` call.... — Marco13, Jun 14 '16 at 10:41
But, using eraser we can delete some part of the line. So if I omit the drawLine() method, then the total line will gets removed — Saikiran Gosikonda, Jun 14 '16 at 10:45

score 4 · Accepted Answer · answered Jun 14 '16 at 11:19

Here is the example. To test it you need to replace my image with your background image.

import java.awt.AlphaComposite;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.File;

import javax.imageio.ImageIO;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.WindowConstants;

/**
 * <code>PaintTryout</code>.
 *
 * @author smedvynskyy
 */
public class PaintPanel extends JPanel {

    private Image backgroundImage;

    private BufferedImage paintImage;

    public PaintPanel() {
        try {
            // replace this image with your image
            backgroundImage = ImageIO.read(new File("E:\\icons\\blackboard.png"));
            paintImage = new BufferedImage(backgroundImage.getWidth(this), 
                    backgroundImage.getHeight(this), BufferedImage.TYPE_INT_ARGB);
        } catch (final Exception e) {
            e.printStackTrace();
        }

    }

    public void fillRect() {
        final Graphics g = paintImage.createGraphics();
        g.setColor(Color.RED);
        g.fillRect(0, 0, 50, 50);
        g.dispose();
        repaint();
    }

    public void clearRect() {
        final Graphics2D g = paintImage.createGraphics();
        g.setColor(new Color(0, 0, 0, 0));
        g.setComposite(AlphaComposite.Clear); // overpaint
        g.fillRect(0, 0, 50, 50);
        g.dispose();
        repaint();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(backgroundImage, 0, 0, this);
        g.drawImage(paintImage, 0, 0, this);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Dimension getPreferredSize() {
        return new Dimension(backgroundImage.getWidth(this), 
                backgroundImage.getHeight(this));
    }

    public static void main(String[] args) {
        final JFrame frm = new JFrame("Tesp paint");
        final PaintPanel p = new PaintPanel();
        frm.add(p);
        final JPanel buttons = new JPanel();
        final JButton fill = new JButton("Fill Rect");
        fill.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                p.fillRect();
            }
        });
        final JButton clear = new JButton("Clear Rect");
        clear.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                p.clearRect();
            }
        });
        buttons.add(fill);
        buttons.add(clear);
        frm.add(buttons, BorderLayout.SOUTH);
        frm.pack();
        frm.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frm.setLocationRelativeTo(null);
        frm.setVisible(true);
    }
}

Medvyncskyy Using the above solution, when I try to erase something I am getting black color rectangles — Saikiran Gosikonda, Oct 25 '16 at 07:13
It is working fine with the above example. But, when I use it in my code to modify buffered image I am getting black coloured rectangles. — Saikiran Gosikonda, Oct 25 '16 at 11:18
It is working perfectly. Previously, I have used clearRect() instead of fillRect(). Now, everything is good. Thanks a lot — Saikiran Gosikonda, Nov 01 '16 at 09:30

score 0 · Answer 2 · answered Jun 14 '16 at 11:40

0

The easy way to do this is to draw the lines in XOR mode. Then, to erase them, you just draw them again.

answered Jun 14 '16 at 11:40

user207421

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In this case we will get not a solid one color line, but a XOR-pixel line. – Sergiy Medvynskyy Jun 14 '16 at 11:48
In this case the whole line will gets removed or added. But using eraser we should have the capability to erase particular part of the line also. In that case, this may not work – Saikiran Gosikonda Jun 14 '16 at 11:49
@SaikiranGosikonda No, in this case whatever part of the line you redraw will be erased. – user207421 Jun 14 '16 at 21:43
@EJP Is it works same for all other shapes also. Like Rectangle, Circle – Saikiran Gosikonda Jun 15 '16 at 02:53
@SergiyMedvynskyy Indeed, but that is often an advantage. Consider a line drawn over a surface whose background changes from black to white, as an extreme example. – user207421 Jun 15 '16 at 04:06
@SaikiranGosikonda It works for anything. Surely this is obvious? A ^ B ^ B = A. This is a standard graphics technique. I'm amazed nobody here appears to have heard of it. I was doing it 25 years ago. – user207421 Jun 15 '16 at 04:07
@EJP Can you please provide an working example for it – Saikiran Gosikonda Oct 25 '16 at 06:12

How to delete shapes drawn on an Image

2 Answers2