/*
 *    GeoTools - The Open Source Java GIS Toolkit
 *    http://geotools.org
 *
 *    (C) 2011, Open Source Geospatial Foundation (OSGeo)
 *    (C) 2008, Open Geospatial Consortium Inc.
 *    
 *    All Rights Reserved. http://www.opengis.org/legal/
 */
package org.opengis.style;

import org.opengis.annotation.Extension;
import org.opengis.annotation.XmlElement;
import org.opengis.filter.expression.Expression;


/**
 * The Displacement gives the X and Y displacements from the original geometry. This
 * element may be used to avoid over-plotting of multiple PolygonSymbolizers for one
 * geometry or supplying "shadows" of polygon gemeotries. The displacements are in units
 * of pixels above and to the right of the point. The default displacement is X=0, Y=0.
 *
 *
 * @source $URL: http://svn.osgeo.org/geotools/trunk/modules/library/opengis/src/main/java/org/opengis/style/Displacement.java $
 * @version <A HREF="http://www.opengeospatial.org/standards/symbol">Symbology Encoding Implementation Specification 1.1.0</A>
 * @author Open Geospatial Consortium
 * @author Johann Sorel (Geomatys)
 * @author Ian Turton, CCG
 * @since GeoAPI 2.2
 */
@XmlElement("Displacement")
public interface Displacement {

    /**
     * Returns an expression that computes a pixel offset from the geometry
     * point.  This offset point is where the text's anchor point gets
     * located. If this expression is null, the default offset of zero is
     * used.
     *
     * @return Expression
     */
    @XmlElement("DisplacementX")
    Expression getDisplacementX();

    /**
     * Returns an expression that computes a pixel offset from the geometry
     * point.  This offset point is where the text's anchor point gets
     * located. If this expression is null, the default offset of zero is
     * used.
     *
     * @return Expression
     */
    @XmlElement("DisplacementY")
    Expression getDisplacementY();

    /**
     * calls the visit method of a StyleVisitor
     *
     * @param visitor the style visitor
     */
    @Extension
    Object accept(StyleVisitor visitor, Object extraData);
    
}