Re: [JAVA2D] scale and translate question

[Ted Hill]

I posted a question yesterday on scaling and translating, I think I have found my answer.   I don't understand all the details, but it looks like after calling the scale( ), the translate( ) call must also be scaled:       protected void paintComponent(Graphics g)     {         super.paintComponent(g);           Graphics2D g2 = (Graphics2D) g;           final int   width      = bufImage.getWidth( );         final int   height     = bufImage.getHeight( );         final float zoomFactor = getZoomFactor( );           // translate by half the 'growth'         float translateX       = 0.5f * ((width  * zoomFactor) - width);         float translateY       = 0.5f * ((height * zoomFactor) - height);           // make image larger         g2.scale(zoomFactor, zoomFactor);           // keep image center centered         g2.translate( - (translateX * (1/zoomFactor)), - (translateY * (1/zoomFactor)) );                  g2.drawImage(bufImage, 0, 0, this);     }   In the above code, I multiply my translateX and translateY by the inverse of the zoomFactor which was used to do the scaling. Now as the image gets bigger, it stays centered.   Ted Hill ----- Original Message ----- From: Ted Hill To: [EMAIL PROTECTED] Sent: Tuesday, August 29, 2000 4:58 PM Subject: [JAVA2D] scale and translate question Hello,   I am trying to implement a zoom on a BufferedImage. I have extended a JPanel and a simplified version of its paintComponent( ) is shown below.   Each time paintComponent is called, the zoomFactor is increased by 0.1. So the first time it is called zoomFactor is 1.0, then 1.1, then 1.2 etc.   After calling scale( ), I call translate( ) to move the image up and to the left in an effort to keep the center of the image centered. However, what I find is: as the image grows larger, the center keeps moving up and to the left until it 'floats' off the panel.   I guess I'm using the wrong value for translate( ) but can't figure out what it should be. I would think that it should be half of the 'growth', i.e.  0.5f * ((width  * zoomFactor) - width);          Am I making an obvious error?   Thank you,   Ted Hill =======================       protected void paintComponent(Graphics g)     {         super.paintComponent(g);           Graphics2D g2 = (Graphics2D) g;           final int   width      = bufImage.getWidth( );         final int   height     = bufImage.getHeight( );         final float zoomFactor = getZoomFactor( );           // translate by half the 'growth'         float translateX       = 0.5f * ((width  * zoomFactor) - width);         float translateY       = 0.5f * ((height * zoomFactor) - height);           // make image larger         g2.scale(zoomFactor, zoomFactor);           // keep image center centered         g2.translate( - translateX, - translateY );                  g2.drawImage(bufImage, 0, 0, this);     }