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/PrimitiveRenderEvent.java
*/
	public static final int FILL = 2;
	/**
	 * An index value used internally. Note this is public only for
	 * cross-package internal access.
	 */
	public int iObjIndex = 0;
	private double dDepth = 0;
	/**
	 * Creates a Primitive Render Event from a source object. The source can be
	 * of any type. Inside the chart engine, it is a StructureSource object
	 * 
	 * @param oSource
	 *            The Source Object
	 * @see StructureSource
	 */
	public PrimitiveRenderEvent( Object oSource )
	{
		super( oSource );
	}
	/**
	 * Returns the mimimum bounds required to contain the rendering area for
	 * current event.
	 * 
	 * @return
	 * @throws ChartException
	 *             if not implemented by concrete class
	 */
	public Bounds getBounds( ) throws ChartException
	{