hu.kazocsaba.imageviewer

Class Overlay

java.lang.Object

hu.kazocsaba.imageviewer.Overlay

Direct Known Subclasses:

PixelMarkerOverlay

public abstract class Overlay
extends Object

An overlay is a layer on top of an image. It can be used to add annotations, arbitrary shapes to an image. Drawing is implemented in the paint method.

The following is an implementation of a simple example overlay that draws a cross over the image:

 
 class XPainter extends Overlay {
   public void paint(Graphics2D g, BufferedImage image, AffineTransform transform) {
     g.setColor(Color.RED);
     double[] bounds={
       0, 0, 
       image.getWidth(), 0,
       image.getWidth(), image.getHeight(),
       0, image.getHeight()};
     transform.transform(bounds, 0, bounds, 0, 4);
     g.drawLine((int)bounds[0], (int)bounds[1], (int)bounds[4], (int)bounds[5]);
     g.drawLine((int)bounds[2], (int)bounds[3], (int)bounds[6], (int)bounds[7]);
   }
 }
 

It can be added to a viewer by calling viewer.addOverlay(new XPainter(), 10).

Author:

Kazó Csaba

Constructor Summary

Constructors

Constructor and Description
Overlay()

Method Summary

Methods

Modifier and Type	Method and Description
abstract void	paint(Graphics2D g, BufferedImage image, AffineTransform transform) Called to paint the contents of this overlay.
void	repaint() Causes the overlay to be repainted.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Overlay

public Overlay()

Method Detail

repaint

public void repaint()

Causes the overlay to be repainted.

paint

public abstract void paint(Graphics2D g,
         BufferedImage image,
         AffineTransform transform)

Called to paint the contents of this overlay. The graphics context to paint on is a copy for this overlay and can be freely modified.

The method receives the currently displayed image. The image is never null - if there is currently no image being displayed in the image viewer, then the paint method is not called.

This method also receives the transformation that is applied to the image before it is displayed. This transformation is most commonly the concatenation of a uniform scale and a translation. The original image bounds (0, 0) - (image.getWidth(), image.getHeight()) are mapped using this transformation to get the final display bounds. The overlay should not rely on whether painting outside these final bounds will be visible or not.

Parameters:

g - the graphics context to draw onto

image - the current image

transform - the transformation applied to the image before displaying