在屏幕上查找 AffineTransform 原点

Question

假设我有一个 AffineTransform (transform) 并调用了它的一堆方法。可以说我旋转并翻译它。然后我用它转换一个图形对象（g2d）：

g2d.transform(transform);

我想在 我的屏幕 上找到我的新 (0, 0) 所在的坐标。因此，如果我在这些坐标处用未转换的g2d 绘制一个矩形，而用我的转换后的g2d 绘制一个矩形，它们将重叠。那么我如何才能得到这一点，我是否需要做一些数学运算，AffineTransform 或 Graphics2D 是否有内置方式（我找不到）？

Answer 1

你可以...

创建原始 Graphics 上下文 (Graphics#create) 的副本（这始终是一个好主意）然后将转换应用于副本（这将使原始不受影响，只是不要忘记 dispose完成后的副本）

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private BufferedImage img;

        public TestPane() {
            try {
                img = ImageIO.read(your source image here...);
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }

        @Override
        public Dimension getPreferredSize() {
            return img == null ? new Dimension(200, 200) : new Dimension(img.getWidth(), img.getHeight());
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            int x = (getWidth() - img.getWidth()) / 2;
            int y = (getHeight() - img.getHeight()) / 2;
            AffineTransform at = AffineTransform.getTranslateInstance(x, y);
            at.rotate(Math.toRadians(180), img.getWidth() / 2, img.getHeight() / 2);
            g2d.setTransform(at);
            g2d.drawImage(img, 0, 0, this);
            g2d.dispose();

            // I don't like touching the original ;)
            g2d = (Graphics2D) g.create();
            FontMetrics fm = g2d.getFontMetrics();
            g2d.drawString("Top Left", 0, 0 + fm.getAscent());

            String txt = "Bottom right";
            g2d.drawString(txt, getWidth() - fm.stringWidth(txt) - 1, ((getHeight() - fm.getHeight()) - 1) + fm.getAscent());
            g2d.dispose();
        }

    }

}

你可以...

反转转换，如果它是一个复杂的转换总是很棘手......

你可以...

首先获取对原始转换的引用，应用新转换，绘制您需要绘制的任何内容，然后重新应用原始转换

你可以...

使用AffineTransform#setToIdentity 将转换“重置”回其原始状态...

    AffineTransform at = g2d.getTransform();
    at.translate(x, y);
    at.rotate(Math.toRadians(180), img.getWidth() / 2, img.getHeight() / 2);
    // Some drawing...

    at.setToIdentity();
    g2d.setTransform(at);
    // Back to basics