question: 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 ( ) ; }
target:  Perform a zooming operation centered on the given point (dx, dy) and using the given scale factor. The given AffineTransform instance is preconcatenated.