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
/**
	 * Returns the meta object for class '{@link org.eclipse.birt.chart.model.attribute.Polygon <em>Polygon</em>}'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return the meta object for class '<em>Polygon</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.Polygon
	 * @generated
	 */
	EClass getPolygon( );
	/**
	 * Returns the meta object for the containment reference list '{@link org.eclipse.birt.chart.model.attribute.Polygon#getPoints <em>Points</em>}'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return the meta object for the containment reference list '<em>Points</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.Polygon#getPoints()
	 * @see #getPolygon()
	 * @generated
	 */
	EReference getPolygon_Points( );
	/**
	 * Returns the meta object for class '{@link org.eclipse.birt.chart.model.attribute.Rotation3D <em>Rotation3 D</em>}'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return the meta object for class '<em>Rotation3 D</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.Rotation3D
	 * @generated
	 */
	EClass getRotation3D( );
	/**
	 * Returns the meta object for the containment reference list '{@link org.eclipse.birt.chart.model.attribute.Rotation3D#getAngles <em>Angles</em>}'.