反向 Java Graphics2D 缩放和旋转坐标 [英] Reverse Java Graphics2D scaled and rotated coordinates

问题描述

我在 Java 中使用 Graphics2D 来缩放和旋转我绘制的图片.我现在希望能够知道当我点击图片中的某个点时原始坐标是什么.因此，考虑到旋转和缩放的坐标，我想计算原始坐标.有没有简单的方法可以做到这一点?

I use Graphics2D in Java to scale and rotate the picture I draw. I now want to be able to tell what the original coordinates were when I click on a certain point in the picture. So given the rotated and scaled coordinates I want to calculate the original ones. Is there a simple way to do this?

推荐答案

如果你保留一份你在绘制图像时使用的 AffineTransform 的副本，你可以使用AffineTransform.inverseTransform(Point2D ptSrc, Point2D ptDst)将设备空间坐标转换回用户空间

If you keep a copy of the AffineTransform you use when you paint the image, you can use AffineTransform.inverseTransform(Point2D ptSrc, Point2D ptDst) to transform a device space coordinate back to user space

编辑:如果您在绘制时捕获 Graphics2D 的当前变换，请注意 Graphics2D 被重复用于多个轻量级子项同一个窗口/面板，因为这样变换将相对于父组件，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:

Edit: If you capture the current transform of the Graphics2D while painting, beware of the Graphics2D being re-used for multiple lightweight children of the same window/panel, because then the transform will be relative to the parent component but the mouse coordinates will be relative to the child. You need to capture the changes you make 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.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;
}

这篇关于反向 Java Graphics2D 缩放和旋转坐标的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！