public void centerZoom(double dx,double dy,double scale,AffineTransform af){
  af.preConcatenate(AffineTransform.getTranslateInstance(-dx,-dy));
  af.preConcatenate(AffineTransform.getScaleInstance(scale,scale));
  af.preConcatenate(AffineTransform.getTranslateInstance(dx,dy));
  transform=af;
  syncScrollBars();
}

public void centerZoom ( double dx , double dy , double scale , AffineTransform af ) { af . preConcatenate ( AffineTransform . getTranslateInstance ( - dx , - dy ) ) ; af . preConcatenate ( AffineTransform . getScaleInstance ( scale , scale ) ) ; af . preConcatenate ( AffineTransform . getTranslateInstance ( dx , dy ) ) ; transform = af ; syncScrollBars ( ) ; }
perform a zooming operation centered on the given point ( dx , dy ) and using the given scale factor . the given affinetransform instance is preconcatenated .
