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.engine/src/org/eclipse/birt/chart/model/attribute/AttributePackage.java
*/
	int PALETTE__ENTRIES = 1;
	/**
	 * The number of structural features of the the '<em>Palette</em>' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int PALETTE_FEATURE_COUNT = 2;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.PolygonImpl <em>Polygon</em>}' class.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.PolygonImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getPolygon()
	 * @generated
	 */
	int POLYGON = 25;
	/**
	 * The feature id for the '<em><b>Points</b></em>' containment reference list.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int POLYGON__POINTS = 0;
	/**
	 * The number of structural features of the the '<em>Polygon</em>' class.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->