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/MarkerInstruction.java
assert false;
				return -1;
			}
		}
		else if ( o instanceof WrappedInstruction )
		{
			bo = ( (WrappedInstruction) o ).getBounds( );
		}
		return ( dc != null && dc.isTransposed( ) )
				? PrimitiveRenderEvent.compareTransposed( getBounds( ), bo )
				: PrimitiveRenderEvent.compareRegular( getBounds( ), bo );
	}
	/**
	 * Returns the associated event.
	 * 
	 * @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( )