question: private void drawMagnifyMask ( Graphics2D g ) { double viewWidth = viewport . getWidthInView ( ) ; double viewHeight = viewport . getHeightInView ( ) ; float minExtent = ( float ) Math . min ( viewWidth , viewHeight ) ; float maskWidth = ( float ) ( minExtent * AppConstants . MASK_WIDTH_FRAC / 2 ) ; Area mask = new Area ( new Rectangle2D . Float ( ( float ) 0 , ( float ) 0 , ( float ) viewWidth , ( float ) viewHeight ) ) ; Area maskHole = new Area ( new Rectangle2D . Float ( ( float ) maskWidth , ( float ) maskWidth , ( ( float ) viewWidth ) - 2 * maskWidth , ( ( float ) viewHeight ) - 2 * maskWidth ) ) ; mask . subtract ( maskHole ) ; g . setColor ( AppConstants . MASK_CLR ) ; g . fill ( mask ) ; }
target:  Draws a mask surround to indicate that geometry is being visually altered