libgdx: rotate a rectangle shape (matrix math calculation).

rotate-libgdx-matrix-math.txt

Rectangle rectangle = (Rectangle)shape;

Vector2 center = new Vector2();
rectangle.getCenter(center);

Affine2 transform = new Affine2();
transform.translate(rectangle.x, rectangle.y + rectangle.height);
transform.rotate(-rotation);
transform.translate(-rectangle.x, -rectangle.y - rectangle.height);
transform.applyTo(center);