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Batik Java2D SVG generator
There is a newer version: 1.17
/*

   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

 */
package org.apache.batik.svggen;

import java.awt.Shape;
import java.awt.geom.GeneralPath;
import java.awt.geom.Line2D;

import org.apache.batik.ext.awt.g2d.GraphicContext;
import org.w3c.dom.Element;

/**
 * Utility class that converts a Path object into an SVG clip
 *
 * @author Vincent Hardy
 * @version $Id$
 */
public class SVGClip extends AbstractSVGConverter {
    /**
     * Constant used for some degenerate cases
     */
    public static final Shape ORIGIN = new Line2D.Float(0,0,0,0);

    /**
     * Descriptor to use where there is no clip on an element
     */
    public static final SVGClipDescriptor NO_CLIP =
        new SVGClipDescriptor(SVG_NONE_VALUE, null);

    /**
     * Used to convert clip object to SVG elements
     */
    private SVGShape shapeConverter;

    /**
     * @param generatorContext used to build Elements
     */
    public SVGClip(SVGGeneratorContext generatorContext) {
        super(generatorContext);
        this.shapeConverter = new SVGShape(generatorContext);
    }

    /**
     * Converts part or all of the input GraphicContext into
     * a set of attribute/value pairs and related definitions.
     * @param gc GraphicContext to be converted
     * @return descriptor of the attributes required to represent
     *         some or all of the GraphicContext state, along
     *         with the related definitions
     * @see org.apache.batik.svggen.SVGDescriptor
     */
    public SVGDescriptor toSVG(GraphicContext gc) {
        Shape clip = gc.getClip();

        SVGClipDescriptor clipDesc = null;

        if (clip != null) {
            StringBuffer clipPathAttrBuf = new StringBuffer(URL_PREFIX);

            // First, convert to a GeneralPath so that the
            GeneralPath clipPath = new GeneralPath(clip);

            // Check if this object is already in the Map
            ClipKey clipKey = new ClipKey(clipPath, generatorContext);
            clipDesc = (SVGClipDescriptor)descMap.get(clipKey);

            if (clipDesc == null) {
                Element clipDef = clipToSVG(clip);
                if (clipDef == null)
                    clipDesc = NO_CLIP;
                else {
                    clipPathAttrBuf.append(SIGN_POUND);
                    clipPathAttrBuf.append(clipDef.getAttributeNS(null, SVG_ID_ATTRIBUTE));
                    clipPathAttrBuf.append(URL_SUFFIX);

                    clipDesc = new SVGClipDescriptor(clipPathAttrBuf.toString(),
                                                     clipDef);

                    descMap.put(clipKey, clipDesc);
                    defSet.add(clipDef);
                }
            }
        } else
            clipDesc = NO_CLIP;

        return clipDesc;
    }

    /**
     * In the following method, an clipping Shape is converted to
     * an SVG clipPath.
     *
     * @param clip path to convert to an SVG clipPath
     *        element
     */
    private Element clipToSVG(Shape clip) {
        Element clipDef =
            generatorContext.domFactory.createElementNS(SVG_NAMESPACE_URI,
                                                        SVG_CLIP_PATH_TAG);
        clipDef.setAttributeNS(null, SVG_CLIP_PATH_UNITS_ATTRIBUTE,
                               SVG_USER_SPACE_ON_USE_VALUE);

        clipDef.setAttributeNS(null, SVG_ID_ATTRIBUTE,
                               generatorContext.
                               idGenerator.generateID(ID_PREFIX_CLIP_PATH));

        Element clipPath = shapeConverter.toSVG(clip);
        // unfortunately it may be null because of SVGPath that may produce null
        // SVG elements.
        if (clipPath != null) {
            clipDef.appendChild(clipPath);
            return clipDef;
        } else {
            // Here, we know clip is not null but we got a
            // null clipDef. This means we ran into a degenerate 
            // case which in Java 2D means everything is clippped.
            // To provide an equivalent behavior, we clip to a point
            clipDef.appendChild(shapeConverter.toSVG(ORIGIN));
            return clipDef;
        }
    }
}

/**
 * Inner class used to key clip definitions in a Map.
 * This is needed because we need to test equality
 * on the value of GeneralPath and GeneralPath's equal
 * method does not implement that behavior.
 */
class ClipKey {
    /**
     * This clip hash code. Based on the serialized path
     * data
     */
    int hashCodeValue = 0;

    /**
     * @param proxiedPath path used as an index in the Map
     */
    public ClipKey(GeneralPath proxiedPath, SVGGeneratorContext gc){
        String pathData = SVGPath.toSVGPathData(proxiedPath, gc);
        hashCodeValue = pathData.hashCode();
    }

    /**
     * @return this object's hashcode
     */
    public int hashCode() {
        return hashCodeValue;
    }

    /**
     * @param clipKey object to compare
     * @return true if equal, false otherwise
     */
    public boolean equals(Object clipKey) {
        return clipKey instanceof ClipKey
            && hashCodeValue == ((ClipKey) clipKey).hashCodeValue;
    }
}