Zooming of Shapes Problem - Shapes also translate

Question

Hi,
i have the following problem, i wish to zoom a shape - the problem is - while the shape zooms - it also moves away from my screen - instead of staying at its original point and just growing and growing it grows & moves away - im not sure where the error is.
Pseudo Code :
zoomTrans = AffineTransform.getScaleInstance(1.1,1.1);
while(true) {
zoomingShape = mergeTrans.createTransformedShape(zoomingShape);
zoomingShape.draw(g);
Do i have to add a negative translation here which removes the translation done by the zooming ? Im quiet confused - i thought scaling was working like rotation..
Thanks

Answer 1

You have to translate like Dr Las said. One way is to
translate the center of your shape to (0,0), scale it,
then translate it back to the correct position.
JonIndeed. Scaling has a fixed point: imagine pinning your shape to the X-Y plane; scaling won't cause that point to move. For the basic scale transform, that fixed point is the origin. So choose your fixed point (In the code below it is (1,2), the upper-left corner of the rectangle), and as Jon writes translate it to the origin, scale then translate it back:
import java.awt.*;
import java.awt.geom.*;
public class X {
    public static void main(String[] args)  {
        Shape shape = new Rectangle2D.Float(1,2,3,4); //x,y,w,h
        dump(shape);
        AffineTransform xform = getScale(2, 2, 1, 2);
        dump(xform.createTransformedShape(shape));
    static void dump(Shape shape) {
        float[] coords = new float[6];
        System.out.println("Shape dump:");
        for (PathIterator i = shape.getPathIterator(null);!i.isDone(); i.next()) {
            switch(i.currentSegment(coords)) {
            case PathIterator.SEG_MOVETO:
                System.out.println("move to (" + coords[0] + "," + coords[1] + ")");
                break;
            case PathIterator.SEG_LINETO:
                System.out.println("line to (" + coords[0] + "," + coords[1] + ")");
                break;
            case PathIterator.SEG_CLOSE:
                System.out.println("close");
                break;
            default:
                System.out.println("to lazy to write other cases");
    static AffineTransform getScale(double sx, double sy, double tx, double ty) {
        AffineTransform xform = AffineTransform.getTranslateInstance(tx, ty);
        xform.scale(sx, sy);
        xform.translate(-tx, -ty);
        return xform;