反转 Java Graphics2D 缩放和旋转坐标

Question

我在 Java 中使用 Graphics2D 来缩放和旋转我绘制的图片。我现在想知道当我点击图片中的某个点时原始坐标是什么。所以给定旋转和缩放的坐标，我想计算原始坐标。有没有简单的方法来做到这一点？

Answer 1

如果您保留了绘制图像时使用的 AffineTransform 的副本，则可以使用 AffineTransform.inverseTransform(Point2D ptSrc, Point2D ptDst) 将设备空间坐标转换回用户空间

编辑：如果您在绘制时捕获Graphics2D 的当前变换，请注意Graphics2D 被重新用于同一窗口/面板的多个轻量级子级，因为那样的话transform 将相对于父组件，但鼠标坐标将相对于子组件。您需要捕获对转换所做的更改，而不是其最终值。示例：

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.Box;
import javax.swing.BoxLayout;
import javax.swing.JComponent;
import javax.swing.JFrame;

public class Main {
    public static void main(String[] args) throws MalformedURLException, IOException {
        JFrame frame = new JFrame();
        Box box = new Box(BoxLayout.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);
        box.add(new ImageView(image, xfrm1));
        AffineTransform xfrm2 = AffineTransform.getShearInstance(0.1, 0.2);
        xfrm2.scale(1.3, 0.9);
        box.add(new ImageView(image, xfrm2));
        frame.add(box);
        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, 0, 0, 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;
}

Answer 2

目前尚不清楚您是如何旋转和缩放的。但您可能使用的是AffineTransform。幸运的是，有一个createInverse() 方法和一个inverseTransform() 方法。

所以你的代码可能是

AffineTransform transform = AffineTransform.rotate(theta);
transform.scale(sx, sy);

然后要反转，你可以说

Point2D pointInOrigCoords = transform.inverseTransform(clickPoint,null);

Answer 3

没那么难 ;-)

1. 当您重绘组件时，使用g2.getTransform() 转换后保存AffineTransform

2. 然后调用函数invert()就可以了

3. 在mouseClicked() 事件中我们使用以下代码：

   Point2D p= trans.transform(new Point2D.Double(evt.getX(), evt.getY()), null);
   System.out.println("click x="+p.getX()+" y="+p.getY());
   

就是这样！