SetPosition of an Image after Rotation with Affinetransform

Question

I want to roatate an Image with Affinetransform

I did it like this:

AffineTransform at = AffineTransform.getTranslateInstance(image.getWidth(null), image.getHeight(null));
at.rotate(Math.toRadians(getRadian()),image.getWidth(null)/2, image.getHeight(null)/2);
Graphics2D g2d = (Graphics2D) g;
g2d.drawImage(image, at, null);

But now I want to set the Position of the Image,how do I do this?

Thanks for help

Answer 1

First of all it's unclear which position of image you want to translate to necessary place. Let me propose general rule. Suppose that you want to be able to rotate image around its internal coordinates (ix,iy) and then place this internal position to new global place with coordinates (gx, gy). And rotation angle is "angleInRadians". Then your transformation will be:

    AffineTransform at = AffineTransform.getTranslateInstance(gx, gy);
    at.rotate(angleInRadians);
    at.translate(-ix, -iy);

Do you see back order of events here? It's because of how transformation matrices are applied to each other and to position vector. If you read this from the end to beginning then what we do is we move internal position to coordinate start, then we rotate around this start and then we move this start to necessary global place.

If you need to move center of image then:

    double ix = imageWidth / 2;
    double iy = imageHeight / 2;

If you want to move left upper corner then ix = 0 and iy = 0, so you can skip at.translate(-ix, -iy) in this case.