Doing one transform on a shape after another...

Question

Hi - I am writing a program to create computer artwork and have run into a problem. If I start with a shape (such as a square) and then do a rotation on it I get a diamond... fine... but now what I want to do is stretch the diamond in the x and y directions. For this I'd use scale, but, my problem is that, because the coordinate system was shiftted by the first transform, when I scale in y (for example) the diamond doesn't become stretched, but instead stretches along the old co-ordinate system, so in fact you can see that it is in fact stretching the original square, rather than the new diamond.
I thought about creating a buffered image from the shape and then stretching that but it's not really great to do that in terms of the rest of my program. Is there any way of doing one transform and then resetting the co-ordinate system so that any further transform I do will apply to the new shape rather than the old one?
Thanks in advance for any help - I'm really stuck here and I can't believe that you can't do this in Java!
Olly

Answer 1

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.AffineTransform;
import javax.swing.*;
public class TransformTest extends JPanel
    Shape shape;
    protected void paintComponent(Graphics g)
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        if(shape == null)
            initShape();
        g2.draw(shape);
        double theta = -Math.PI/4.0;
        Rectangle r = shape.getBounds();
        AffineTransform at =
            AffineTransform.getRotateInstance(theta, r.getCenterX(), r.getCenterY());
        Shape diamond = at.createTransformedShape(shape);
        g2.setPaint(Color.red);
        g2.draw(diamond);
        double xScale = 1.5;
        double yScale = 1.0;
        r = diamond.getBounds();
        double x = (1.0 - xScale) * r.getCenterX();
        double y = (1.0 - yScale) * r.getCenterY();
        at.setToTranslation(x, y);
        at.scale(xScale, yScale);
        diamond = at.createTransformedShape(diamond);
        g2.setPaint(Color.blue);
        g2.draw(diamond);
    private void initShape()
        int w = getWidth();
        int h = getHeight();
        int s = Math.min(w,h)/3;
        int x = (w - s)/2;
        int y = (h - s)/2;
        shape = new Rectangle(x, y, s, s);
    public static void main(String[] args)
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setContentPane(new TransformTest());
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
}