Inverting Java graphics2d scaling and rotation coordinates

I use graphics2d in Java to scale and rotate the pictures I draw I now want to be able to tell what the original coordinates are when I click on a point in the picture Therefore, considering the coordinates of rotation and scaling, I want to calculate the original coordinates Is there a simple way?

Solution

If you keep a copy of the affinetransform you used when drawing the image, you can use

Edit: if you capture the current transformation of graphics2d when drawing, please note that graphics2d is reused in multiple lightweight children of the same window / panel, because at that time, the transformation will be relative to the parent component, but the mouse coordinates will be relative to the child You need to capture the changes made to the transform, not its final value Example:

import java.awt.Basicstroke;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.awt.geom.AffineTransform;
import java.awt.geom.NoninvertibleTransformException;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;

import javax.imageio.ImageIO;
import javax.swing.@R_257_2419@;
import javax.swing.@R_257_2419@Layout;
import javax.swing.JComponent;
import javax.swing.JFrame;

public class Main {
    public static void main(String[] args) throws MalformedURLException,IOException {
        JFrame frame = new JFrame();
        @R_257_2419@ @R_257_2419@ = new @R_257_2419@(@R_257_2419@Layout.Y_AXIS);
        BufferedImage image = ImageIO.read(new URL("http://sstatic.net/so/img/logo.png"));
        AffineTransform xfrm1 = AffineTransform.getScaleInstance(0.95,1.25);
        xfrm1.rotate(-0.3);
        @R_257_2419@.add(new ImageView(image,xfrm1));
        AffineTransform xfrm2 = AffineTransform.getShearInstance(0.1,0.2);
        xfrm2.scale(1.3,0.9);
        @R_257_2419@.add(new ImageView(image,xfrm2));
        frame.add(@R_257_2419@);
        frame.pack();
        frame.setDefaultCloSEOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

@SuppressWarnings("serial")
class ImageView extends JComponent {
    @Override
    public void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        try {
            paintXfrm = g2d.getTransform();
            paintXfrm.invert();
            g2d.translate(getWidth() / 2,getHeight() / 2);
            g2d.transform(xfrm);
            g2d.translate(image.getWidth() * -0.5,image.getHeight() * -0.5);
            paintXfrm.concatenate(g2d.getTransform());
            g2d.drawImage(image,this);
        } catch (NoninvertibleTransformException ex) {
            ex.printStackTrace();
        }
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(image.getWidth() * 2,image.getHeight() * 2);
    }

    ImageView(final BufferedImage image,final AffineTransform xfrm) {
        this.canvas = image.createGraphics();
        canvas.setColor(Color.BLACK);
        canvas.setstroke(new Basicstroke(3.0f));
        this.image = image;
        this.xfrm = xfrm;
        addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                try {
                    mouseDownCoord = e.getPoint();
                    paintXfrm.inverseTransform(mouseDownCoord,mouseDownCoord);
                } catch (NoninvertibleTransformException ex) {
                }
            }

            @Override
            public void mouseExited(MouseEvent e) {
                mouseDownCoord = null;
            }
        });
        addMouseMotionListener(new MouseMotionAdapter() {
            @Override
            public void mouseDragged(MouseEvent e) {
                Point p = e.getPoint();
                try {
                    paintXfrm.inverseTransform(p,p);
                    if (mouseDownCoord != null) {
                        canvas.drawLine(mouseDownCoord.x,mouseDownCoord.y,p.x,p.y);
                        for (Component sibling: getParent().getComponents()) {
                            sibling.repaint();
                        }
                    }
                    mouseDownCoord = p;
                } catch (NoninvertibleTransformException ex) {
                    ex.printStackTrace();
                }
            }
        });
    }

    private Graphics2D canvas;
    private BufferedImage image;
    private AffineTransform xfrm;
    private AffineTransform paintXfrm;
    private Point mouseDownCoord;
}