How to use AffineTransform.quadrantRotate to rotate a bitmap?

Question

I want to rotate a bitmap about its center point, and then draw it into a larger graphics context.

The bitmap is <

Answer 1

The order of your transformation matters. Basically your example code is saying "rotate the image by 90 degrees AND then translate it...."

So, using your code (rotate, then translate) produces...

Switching the order (translate then rotate) produces

...

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
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 javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class TestRotation100 {

    public static void main(String[] args) {
        new TestRotation100();
    }

    public TestRotation100() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                final TestPane testPane = new TestPane();
                final JSlider slider = new JSlider(0, 3);
                slider.addChangeListener(new ChangeListener() {
                    @Override
                    public void stateChanged(ChangeEvent e) {
                        testPane.setQuad(slider.getValue());
                    }
                });
                slider.setValue(0);

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(testPane);
                frame.add(slider, BorderLayout.SOUTH);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private BufferedImage img;
        private int quad = 0;

        public TestPane() {
            try {
                img = ImageIO.read(new File("/Users/swhitehead/Dropbox/MegaTokyo/Rampage_Small.png"));
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }

        public void setQuad(int quad) {
            this.quad = quad;
            repaint();
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();

            AffineTransform at = new AffineTransform();
            at.translate(100, 40);
            at.quadrantRotate(quad, img.getWidth() / 2, img.getHeight() / 2);

            g2d.drawImage(img, at, this);

            g2d.dispose();
        }

    }

}