How to rotate a line based on a given number of degrees

Question

I have a line drawn with a Graphics object. I want to rotate this line a certain amount of degrees based on how much the mouse is dragged. I can get the number of degrees i need to rotate it but how do i then rotate the line based on that?

Thank You!

Answer 1

You can create a Line2D object for your original line. Then you can use AffineTransform#getRotateInstance to obtain an AffineTransform that does the rotation about a certain angle, around a certain point. Using this AffineTransform, you can create a rotated Line2D object to paint. So your painting code could roughly look like this:

protected void paintComponent(Graphics gr) {
    super.paintComponent(gr);
    Graphics2D g = (Graphics2D)gr; 

    // Create the original line, starting at the origin,
    // and extending along the x-axis
    Line2D line = new Line2D.Double(0,0,100,0);

    // Obtain an AffineTransform that describes a rotation
    // about a certain angle (given in radians!), around
    // the start point of the line. (Here, this is the
    // origin, so this could be simplified. But in this
    // form, it's more generic)
    AffineTransform at = 
        AffineTransform.getRotateInstance(
            Math.toRadians(angleInDegrees), line.getX1(), line.getY1());

    // Draw the rotated line
    g.draw(at.createTransformedShape(line));
}