Rotating BufferedImage instances

问题

I am having trouble getting a rotated BufferedImage to display. I think the rotation is working just fine, but I can\'t actually draw it to the screen. My code:

Class extends JPanel {
    BufferedImage img;
    int rotation = 0;

    public void paintComponent(Graphics g) {
        g.clearRect(0, 0, getWidth(), getHeight());
        img2d = img.createGraphics();
        img2d.rotate(Math.toRadians(rotation), img.getWidth() / 2, img.getHeight() / 2);
        g.drawImage(img, imgx, imgy, null);
        this.repaint();
    }
}

This is not working for me. I could not find any way to draw the rotated img2d onto g.

EDIT: I have multiple objects that are being drawn onto g, so I can\'t rotate that. I need to be able to rotate things individually.

回答1:

I would use Graphics2D.drawImage(image, affinetranform, imageobserver).

The code example below rotates and translates an image to the center of the component. This is a screenshot of the result:

 public static void main(String[] args) throws IOException {
    JFrame frame = new JFrame("Test");

    frame.add(new JComponent() {

         BufferedImage image = ImageIO.read(new URL("http://upload.wikimedia.org/wikipedia/en/2/24/Lenna.png"));

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

              // create the transform, note that the transformations happen
              // in reversed order (so check them backwards)
              AffineTransform at = new AffineTransform();

              // 4. translate it to the center of the component
              at.translate(getWidth() / 2, getHeight() / 2);

              // 3. do the actual rotation
              at.rotate(Math.PI/4);

              // 2. just a scale because this image is big
              at.scale(0.5, 0.5);

              // 1. translate the object so that you rotate it around the 
              //    center (easier :))
              at.translate(-image.getWidth()/2, -image.getHeight()/2);

              // draw the image
              Graphics2D g2d = (Graphics2D) g;
              g2d.drawImage(image, at, null);

              // continue drawing other stuff (non-transformed)
              //...

         }
    });

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(400, 400);
    frame.setVisible(true);
}

回答2:

Maybe you should try using AffineTransform like this:

    AffineTransform transform = new AffineTransform();
    transform.rotate(radians, bufferedImage.getWidth()/2, bufferedImage.getHeight()/2);
    AffineTransformOp op = new AffineTransformOp(transform, AffineTransformOp.TYPE_BILINEAR);
    bufferedImage = op.filter(bufferedImage, null);

Hope this helps.

回答3:

You are rotating the graphics for drawing into your image, not the image. Thats why you see no effect. Apply the rotation to the graphics you are painting on and it will draw the image rotated:

public void paintComponent(Graphics g) {
    g.clearRect(0, 0, getWidth(), getHeight());
    g.rotate(Math.toRadians(rotation), img.getWidth() / 2, img.getHeight() / 2);
    g.drawImage(img, imgx, imgy, null);
    this.repaint();
}

This will probably not draw entirely what you expect, the rotation will revolve around the coordinate origin. For the image to be rotate around its center you need to apply a coordinate translation before the rotation, for example:

g.translate(imgx >> 1, imgy >> 1);

The Graphics2D Tutorial has some more examples.

来源：https://stackoverflow.com/questions/4918482/rotating-bufferedimage-instances

标签

java

swing

rotation

bufferedimage

graphics2d