/*
	File: OffsetCanvas.java
	5/29/96   Larry Barowski
*/



   package EDU.auburn.VGJ.gui;


   import java.awt.Dimension;
   import java.awt.Point;
   import java.awt.Canvas;

   import EDU.auburn.VGJ.util.DPoint;
   import EDU.auburn.VGJ.util.DDimension;

/**
 *	This abstract class is used inside a ScrolledPanel, and
 *	implements the required functionality to communicate with it.
 *	</p>Here is the <a href="../gui/OffsetCanvas.java">source</a>.
 *
 *@see		ScrolledPanel
 *@author	Larry Barowski
**/
   public abstract class OffsetCanvas extends Canvas
   {
   
   
   
   
   
   /**
    *	Event id for size change. Subclasses must post an event with this id
    *	when their contents or windows are resized.
    **/
      public static int	RESIZE = 32450;
   
   /**
    *	Event id for changing the label above the OffsetCanvas.
    *	The arg field of the event must contain the string.
    **/
      public static int	LABEL = 32451;
   
   
   
   
   /**
    *	Adjust the offset of the contents of the canvas. These must have the
    *	following meaning: screen position + offset = contents position.
    *	e.g. if xoffset is 10, contents starts 10 pixels to the left of the
    *	screen.
    *
    *@param xoffset horizontal offset
    *@param yoffset vertical offset
    **/
      abstract public void setOffsets(double xoffset, double yoffset, boolean redraw);
   
   
   
   
   
   /**
    *	Return the size of the contents.
    **/
      abstract public DDimension contentsSize();
   
   
   
   
   
   
      abstract public DPoint getOffset()
      ;
   }