在JPanel内部旋转BufferedImage

Question

I am trying to rotate a BufferedImage and display it inside a JLabel (which is inside a JPanel ). The current result produces a white square rotated 10 degrees against a black background, but the image is not present inside the square. I know myPicture is not blank, since myPicture itself displays properly inside the JPanel when not rotated.

Here is the code:

int w = myPicture.getWidth();    

int h = myPicture.getHeight();  

BufferedImage newImage = new BufferedImage(w, h, myPicture.getType());

Graphics2D graphic = newImage.createGraphics();

graphic.rotate(Math.toRadians(10), w/2, h/2);

graphic.drawImage(myPicture, null, 0, 0);

picLabel.setIcon(new ImageIcon(newImage));

Answer 1

There's not a lot to go on, but two things come to mind. It's possible that the image is not been rendered in the correct position after it's been rotated and two, you're not disposing of the Graphics context when you're done with it (not that I believe it should have an effect, but you never know).

This is a simple example that renders the result via paintComponent , but the concept is the same.

It uses an AffineTransformation to rotate the image.

import java.awt.BorderLayout;
import java.awt.Color;
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 java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.UIManager;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class TestRotateImage {

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

    public TestRotateImage() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (Exception ex) {
                }

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

    public class TestPane extends JPanel {

        private JSlider slider;
        private BufferedImage image;

        public TestPane() {
            setLayout(new BorderLayout());

            try {
                image = ImageIO.read(new File("/path/to/your/image"));
            } catch (IOException ex) {
                ex.printStackTrace();
            }

            slider = new JSlider();
            slider.setMinimum(0);
            slider.setMaximum(360);
            slider.setMinorTickSpacing(5);
            slider.setMajorTickSpacing(10);
            slider.setValue(0);
            add(slider, BorderLayout.SOUTH);
            slider.addChangeListener(new ChangeListener() {
                @Override
                public void stateChanged(ChangeEvent e) {
                    repaint();
                }
            });
        }

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

        public double getAngle() {

            return Math.toRadians(slider.getValue());

        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);

            Graphics2D g2d = (Graphics2D) g.create();

            g2d.setColor(Color.RED);
            g2d.drawLine(getWidth() / 2, 0, getWidth() / 2, getHeight());
            g2d.drawLine(0, getHeight() / 2, getWidth(), getHeight() / 2);

            g2d.setColor(Color.BLACK);
            int x = (getWidth() - image.getWidth()) / 2;
            int y = (getHeight() - image.getHeight()) / 2;
            AffineTransform at = new AffineTransform();
            at.setToRotation(getAngle(), x + (image.getWidth() / 2), y + (image.getHeight() / 2));
            at.translate(x, y);
            g2d.setTransform(at);
            g2d.drawImage(image, 0, 0, this);
            g2d.dispose();

        }
    }
}

Update using a JLabel

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
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.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.UIManager;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class TestRotateImage {

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

    public TestRotateImage() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (Exception ex) {
                }

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

    public class TestPane extends JPanel {

        private JSlider slider;
        private BufferedImage image;
        private JLabel label;

        public TestPane() {
            setLayout(new BorderLayout());

            label = new JLabel();
            label.setHorizontalAlignment(JLabel.CENTER);
            label.setVerticalAlignment(JLabel.CENTER);

            try {
                image = ImageIO.read(new File("/path/to/your/image"));
                label.setIcon(new ImageIcon(image));
            } catch (IOException ex) {
                ex.printStackTrace();
            }

            add(label);

            slider = new JSlider();
            slider.setMinimum(0);
            slider.setMaximum(360);
            slider.setMinorTickSpacing(5);
            slider.setMajorTickSpacing(10);
            slider.setValue(0);
            add(slider, BorderLayout.SOUTH);
            slider.addChangeListener(new ChangeListener() {
                @Override
                public void stateChanged(ChangeEvent e) {
                    double radians = Math.toRadians(slider.getValue());
                    double sin = Math.abs(Math.sin(radians));
                    double cos = Math.abs(Math.cos(radians));
                    int newWidth = (int)Math.round(image.getWidth() * cos + image.getHeight() * sin);
                    int newHeight = (int)Math.round(image.getWidth() * sin + image.getHeight() * cos);

                    BufferedImage rotate = new BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_ARGB);
                    Graphics2D g2d = rotate.createGraphics();
                    int x = (newWidth - image.getWidth()) / 2;
                    int y = (newHeight - image.getHeight()) / 2;
                    AffineTransform at = new AffineTransform();
                    at.setToRotation(getAngle(), x + (image.getWidth() / 2), y + (image.getHeight() / 2));
                    at.translate(x, y);
                    g2d.setTransform(at);
                    g2d.drawImage(image, 0, 0, TestPane.this);
                    g2d.dispose();
                    label.setIcon(new ImageIcon(rotate));
                }
            });
        }

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

        public double getAngle() {

            return Math.toRadians(slider.getValue());

        }
    }
}

Answer 2

I solved my own issue. The problem lay in the code:

myPicture.getType()

Since there is a lot of variability in the types of images you could put in to the program, the results are going to be unpredictable when you start drawing into the new BufferedImage. I solved the problem by setting the type explicitly, which in my case required

BufferedImage.TYPE_INT_ARGB

so the full statement read:

BufferedImage newImage = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);