Bug 188283 Bubbles should be z-sorted by size in Bubble charts
Biggest bubbles should be drawn first so that there is no small bubble hidden by a bigger one.
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/event/WrappedInstruction.java
* @return
	 */
	public final PrimitiveRenderEvent getEvent( )
	{
		return pre;
	}
	/**
	 * @return Returns the associated instruction. The value could be one of
	 *         these:
	 *         <ul>
	 *         <li>PrimitiveRenderEvent.DRAW
	 *         <li>PrimitiveRenderEvent.FILL
	 *         </ul>
	 */
	public final int getInstruction( )
	{
		return iInstruction;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see java.lang.Object#toString()
	 */
	public String toString( )
	{
		return Messages.getString( "wrapped.instruction.to.string",  
				new Object[]{
						super.toString( ),
						new Boolean( isModel( ) ),
						getBounds( )