Bug 104986 Backgound image uses an absolute path
Currently Chart uses an absolute path to indicate a backgournd image, that may cause the design unusable on other environments. Expected the background image can be definded in multiple ways like in report designer. e.g. URI(absolute path), File(relative path), Embedded Image(Encoded Image Data).
chart/org.eclipse.birt.chart.device.extension/src/org/eclipse/birt/chart/device/swing/SwingRendererImpl.java
* 
	 * @see org.eclipse.birt.chart.output.IPrimitiveRenderListener#fillPolygon(org.eclipse.birt.chart.output.PolygonRenderEvent)
	 */
	public void fillPolygon( PolygonRenderEvent pre ) throws ChartException
	{
		final Fill flBackground = pre.getBackground( );
		final Location[] loa = pre.getPoints( );
		final int[][] i2a = getCoordinatesAsInts( loa );
		if ( flBackground instanceof ColorDefinition )
		{
			final ColorDefinition cd = (ColorDefinition) flBackground;
			_g2d.setColor( (Color) _ids.getColor( cd ) );
			_g2d.fill( new Polygon( i2a[0], i2a[1], loa.length ) );
		}
		else if ( flBackground instanceof Gradient )
		{
			final Gradient g = (Gradient) flBackground;
			final ColorDefinition cdStart = (ColorDefinition) g.getStartColor( );
			final ColorDefinition cdEnd = (ColorDefinition) g.getEndColor( );
			
			final double dAngleInDegrees = g.getDirection( );
			final double dAngleInRadians = ( ( -dAngleInDegrees * Math.PI ) / 180.0 );
			
			final double dMinX = BaseRenderer.getX( loa, IConstants.MIN );
			final double dMaxX = BaseRenderer.getX( loa, IConstants.MAX );
			final double dMinY = BaseRenderer.getY( loa, IConstants.MIN );
			final double dMaxY = BaseRenderer.getY( loa, IConstants.MAX );
			/*
			 * if (bRadial) { }
			 */