org.geotools.styling.Displacement Maven / Gradle / Ivy

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/*
 *    GeoTools - The Open Source Java GIS Toolkit
 *    http://geotools.org
 *
 *    (C) 2002-2008, Open Source Geospatial Foundation (OSGeo)
 *
 *    This library is free software; you can redistribute it and/or
 *    modify it under the terms of the GNU Lesser General Public
 *    License as published by the Free Software Foundation;
 *    version 2.1 of the License.
 *
 *    This library is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *    Lesser General Public License for more details.
 */
package org.geotools.styling;

import org.geotools.filter.ConstantExpression;
import org.opengis.filter.expression.Expression;
import org.opengis.style.StyleVisitor;

/**
 * A Displacement gives X and Y offset displacements to use for rendering a text label near a point.
 *
 * @author Ian Turton, CCG
 * @version $Id$
 */
public interface Displacement extends org.opengis.style.Displacement {
    /** Default Displacement instance. */
    static final Displacement DEFAULT =
            new ConstantDisplacement() {
                private void cannotModifyConstant() {
                    throw new UnsupportedOperationException("Constant Stroke may not be modified");
                }

                public Expression getDisplacementX() {
                    return ConstantExpression.ZERO;
                }

                public Expression getDisplacementY() {
                    return ConstantExpression.ZERO;
                }

                public Object accept(StyleVisitor visitor, Object extraData) {
                    cannotModifyConstant();
                    return null;
                }
            };

    /** Null Displacement instance. */
    static final Displacement NULL =
            new ConstantDisplacement() {
                private void cannotModifyConstant() {
                    throw new UnsupportedOperationException("Constant Stroke may not be modified");
                }

                public Expression getDisplacementX() {
                    return ConstantExpression.NULL;
                }

                public Expression getDisplacementY() {
                    return ConstantExpression.NULL;
                }

                public Object accept(StyleVisitor visitor, Object extraData) {
                    cannotModifyConstant();
                    return null;
                }
            };

    /**
     * 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 Horizontal offeset
     */
    Expression getDisplacementX();

    /** Sets the expression that computes a pixel offset from the geometry point. */
    void setDisplacementX(Expression x);

    /** Sets the expression that computes a pixel offset from the geometry point. */
    void setDisplacementY(Expression y);

    void accept(org.geotools.styling.StyleVisitor visitor);
}

abstract class ConstantDisplacement implements Displacement {
    private void cannotModifyConstant() {
        throw new UnsupportedOperationException("Constant Displacement may not be modified");
    }

    public void setDisplacementX(Expression x) {
        cannotModifyConstant();
    }

    public void setDisplacementY(Expression y) {
        cannotModifyConstant();
    }

    public void accept(org.geotools.styling.StyleVisitor visitor) {
        cannotModifyConstant();
    }

    public void accept(StyleVisitor visitor) {
        cannotModifyConstant();
    }
}