Easy ways to implement Zoom functionality

Question

Hello,
I have written a small object orientated graph editor that is made of a custom JPanel and custom JComponents. At the moment, device coordinates and user coordinates are the same, - they correspond. Drawing is done via Graphics2D objects.
Is there an easy way to implement a zoom functionality so that device coordinates and user coordinates remain idetically, by just configuring the device (for example via class GraphicsConfiguration ) - so that MouseEvents and all other coordinates are being calculated and converted automatically (Maybe by changing the devices virtual resolution of 72 dpi to another resolution?)
Any help appreciated!
Thanks in advance!
alex

Answer 1

You have to do much work to implement this. Here is the main method that I coded to implement zoom. The whole package is just too large to post here.
* Implements the zoom in, zoom out or zoom functionality according to
* the string <code>command</code> passed in.
* @param command     the command string, one of the three: zoomin,
*     zoomout, zoom
public void zoom(String command) {        
     if(command.equalsIgnoreCase("zoomin")) {
     if(zoomMultiplier+deltZoom > maxZoomMultiplier) return;
          zoomMultiplier = zoomMultiplier+deltZoom;
     } else if(command.equalsIgnoreCase("zoomout")) {
          zoomMultiplier = zoomMultiplier-deltZoom;
          if(zoomMultiplier < minZoomMultiplier)
          zoomMultiplier = minZoomMultiplier;
     } else if(command.equalsIgnoreCase("zoom")) {
          zoomMultiplier = 1.0;
     //Gets the currently visible rectangle's width & height, calculates the new
     //bounds's width & height
     Rectangle rect = getVisibleRect();
     //System.out.println("Contour.zoom getVisibleRect() = "+rect.x+", "+rect.y);
     int newW = (int)((double)rect.width* zoomMultiplier);
     int newH = (int)((double)rect.height* zoomMultiplier);
     //System.out.println("Contour.zoom setBounds = "+newW+", "+newH);
     * Enlarges the component's bounds here & Graph2D.paint() will
     * use this bounds to redraw the contour.
     setBounds(new Rectangle(0, 0, newW, newH));
     //Focuses the currently contents as much as possible
     this.scrollRectToVisible(rect);
     * Changing the size of a scroll pane's client is a two-step process.
     * First, set the client's preferred size. Then, call revalidate on the
     * client to let the scroll pane know that it should update itself and
     * its scroll bars.
     //Update client's preferred size because the area taken up
     //by the graphics has gotten larger or smaller.
     //this.setPreferredSize(new Dimension(rect.width, rect.height));
     this.setPreferredSize(new Dimension(newW, newH));
     //Let the scroll pane know to update itself and its scrollbars.
this.revalidate();                     
Here is some fields used in the method above and the class the method belongs to:
* The multiplier when the zoom in functionality should be carried out.
public double zoomMultiplier = 1.0;
* The increment for each zoom in or out action.
public double deltZoom = 0.2;
* The maximum multiplier in zoom in functionality.
public double maxZoomMultiplier = 20.0;
* The minimum multiplier in zoom in functionality, and
* the currently used value is 1.0.
public double minZoomMultiplier = 1.0;
* The threshold to pan the contour after the PanTo(move)
* button or menu item is activated.
private double deltDistanceToPan = 10.0;
You have to code your method paint() or other methods carrying out the actual painting carefully to make it work with this method harmoniously. It's a too long story to let you know the details here. If you need more discussion, please email me([email protected] or [email protected]. The former address cannot work recently though I pay for it yearly. The latter address is more stable thought it's a free one. You'd better use it.)
Hope this can help.