http://xmlgraphics.apache.org/batik/batik-svggen/: Batik Java2D SVG generator (Apache Software Foundation) 
/*

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   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.util.HashMap;
import java.util.Map;

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


This class is used by the Graphics2D SVG Generator to manage
a group of Nodes that can later be added to the SVG DOM Tree
managed by the DOMTreeManager.
There are two rules that control how children nodes are
added to the group managed by this class:
+ Children node are added to the group as long as
  there is no more than n graphic context overrides needed to
  describe the children style. A graphic context override
  happens when style attributes need to be added to a child
  node to reflect the state of the graphic context at the
  time the child was added. Note that the opacity is never
  reflected in a group node and therefore, is not accounted
  for in the number of overrides. The number of overrides can
  be configured and defaults to 2.
+ Children nodes are added to the current group as long as
  the associated GraphicContext's transform stack is valid.
When children nodes can no longer be added, the group is considered
complete and the associated DOMTreeManager is notified of the
availability of a completed group. Then, a new group is started.


The DOMTreeManager is also notified every thime a new element
is added to the current group. This is needed to let the
DOMTreeManager handle group managers that would be used concurrently.

Author:Christophe Jolif, Vincent Hardy
Version:$Id: DOMGroupManager.java 1804130 2017-08-04 14:41:11Z ssteiner $
/**
 * This class is used by the Graphics2D SVG Generator to manage
 * a group of Nodes that can later be added to the SVG DOM Tree
 * managed by the DOMTreeManager.
 *
 * There are two rules that control how children nodes are
 * added to the group managed by this class:
 *
 * + Children node are added to the group as long as
 *   there is no more than n graphic context overrides needed to
 *   describe the children style. A graphic context override
 *   happens when style attributes need to be added to a child
 *   node to reflect the state of the graphic context at the
 *   time the child was added. Note that the opacity is never
 *   reflected in a group node and therefore, is not accounted
 *   for in the number of overrides. The number of overrides can
 *   be configured and defaults to 2.
 * + Children nodes are added to the current group as long as
 *   the associated GraphicContext's transform stack is valid.
 *
 * When children nodes can no longer be added, the group is considered
 * complete and the associated DOMTreeManager is notified of the
 * availability of a completed group. Then, a new group is started.
 * <br>
 * The DOMTreeManager is also notified every thime a new element
 * is added to the current group. This is needed to let the
 * DOMTreeManager handle group managers that would be used concurrently.
 *
 * @author <a href="mailto:cjolif@ilog.fr">Christophe Jolif</a>
 * @author <a href="mailto:vincent.hardy@eng.sun.com">Vincent Hardy</a>
 * @version $Id: DOMGroupManager.java 1804130 2017-08-04 14:41:11Z ssteiner $
 */
public class DOMGroupManager implements SVGSyntax, ErrorConstants {
    public static final short DRAW = 0x01;
    public static final short FILL = 0x10;

    
Reference to the GraphicContext this manager will use to
reflect style attributes in the tree nodes.

/**
     * Reference to the GraphicContext this manager will use to
     * reflect style attributes in the tree nodes.
     */
    protected GraphicContext gc;

    
DOMTreeManager that this group manager cooperates with

/**
     * DOMTreeManager that this group manager cooperates with
     */
    protected DOMTreeManager domTreeManager;

    
Current group's SVG GraphicContext state

/**
     * Current group's SVG GraphicContext state
     */
    protected SVGGraphicContext groupGC;

    
Current group node

/**
     * Current group node
     */
    protected Element currentGroup;

    
Constructor

Params:
  • gc – graphic context whose state will be reflected in the
          element's style attributes.
  • domTreeManager – DOMTreeManager instance this group manager
       cooperates with.
/**
     * Constructor
     * @param gc graphic context whose state will be reflected in the
     *           element's style attributes.
     * @param domTreeManager DOMTreeManager instance this group manager
     *        cooperates with.
     */
    public DOMGroupManager(GraphicContext gc, DOMTreeManager domTreeManager) {
        if (gc == null)
            throw new SVGGraphics2DRuntimeException(ERR_GC_NULL);

        if (domTreeManager == null)
            throw new SVGGraphics2DRuntimeException(ERR_DOMTREEMANAGER_NULL);

        this.gc = gc;
        this.domTreeManager = domTreeManager;

        // Start with a new Top Level Group
        recycleCurrentGroup();

        // Build the default GC descriptor
        groupGC = domTreeManager.gcConverter.toSVG(gc);
    }

    
Reset the state of this object to handle a new currentGroup

/**
     * Reset the state of this object to handle a new currentGroup
     */
    void recycleCurrentGroup() {
        // Create new initial current group node
        currentGroup = domTreeManager.getDOMFactory().
            createElementNS(SVG_NAMESPACE_URI, SVG_G_TAG);
    }

    
Adds a node to the current group, if possible

Params:
  • element – child Element to add to the group
/**
     * Adds a node to the current group, if possible
     * @param element child Element to add to the group
     */
    public void addElement(Element element) {
        addElement(element, (short)(DRAW|FILL));
    }

    
Adds a node to the current group, if possible

Params:
  • element – child Element to add to the group
/**
     * Adds a node to the current group, if possible
     * @param element child Element to add to the group
     */
    public void addElement(Element element, short method) {
        //
        // If this is the first child to be added to the
        // currentGroup, 'freeze' the style attributes.
        //
        if (!currentGroup.hasChildNodes()) {
            currentGroup.appendChild(element);

            groupGC = domTreeManager.gcConverter.toSVG(gc);
            SVGGraphicContext deltaGC;
            deltaGC = processDeltaGC(groupGC,
                                     domTreeManager.defaultGC);
            domTreeManager.getStyleHandler().
                setStyle(currentGroup, deltaGC.getGroupContext(),
                         domTreeManager.getGeneratorContext());
            if ((method & DRAW) == 0) {
                // force stroke:none
                deltaGC.getGraphicElementContext().put(SVG_STROKE_ATTRIBUTE,
                                                       SVG_NONE_VALUE);
            }
            if ((method & FILL) == 0) {
                // force fill:none
                deltaGC.getGraphicElementContext().put(SVG_FILL_ATTRIBUTE,
                                                       SVG_NONE_VALUE);
            }
            domTreeManager.getStyleHandler().
                setStyle(element, deltaGC.getGraphicElementContext(),
                         domTreeManager.getGeneratorContext());
            setTransform(currentGroup, deltaGC.getTransformStack());
            domTreeManager.appendGroup(currentGroup, this);
        } else {
            if(gc.isTransformStackValid()) {
                //
                // There are children nodes already. Find
                // out delta between current gc and group
                // context
                //
                SVGGraphicContext elementGC =
                    domTreeManager.gcConverter.toSVG(gc);
                SVGGraphicContext deltaGC = processDeltaGC(elementGC, groupGC);

                // If there are less than the maximum number
                // of differences, then add the node to the current
                // group and set its attributes
                trimContextForElement(deltaGC, element);
                if (countOverrides(deltaGC) <= domTreeManager.maxGCOverrides) {
                    currentGroup.appendChild(element);
                    // as there already are children we put all
                    // attributes (group + element) on the element itself.
                    if ((method & DRAW) == 0) {
                        // force stroke:none
                        deltaGC.getContext().
                            put(SVG_STROKE_ATTRIBUTE, SVG_NONE_VALUE);
                    }
                    if ((method & FILL) == 0) {
                        // force fill:none
                        deltaGC.getContext().
                            put(SVG_FILL_ATTRIBUTE, SVG_NONE_VALUE);
                    }
                    domTreeManager.getStyleHandler().
                        setStyle(element, deltaGC.getContext(),
                                 domTreeManager.getGeneratorContext());
                    setTransform(element, deltaGC.getTransformStack());
                } else {
                    //
                    // Need to create a new current group
                    //
                    currentGroup =
                        domTreeManager.getDOMFactory().
                        createElementNS(SVG_NAMESPACE_URI, SVG_G_TAG);
                    addElement(element, method);
                }
            } else {
                //
                // Transform stack is invalid. Create a new current
                // group and validate the stack
                //
                currentGroup =
                    domTreeManager.getDOMFactory().
                    createElementNS(SVG_NAMESPACE_URI, SVG_G_TAG);
                gc.validateTransformStack();
                addElement(element, method);
            }
        }
    }

    
Analyses the Map to define how many attributes constitute
overrides. Only differences in the group context are considered
overrides.

/**
     * Analyses the Map to define how many attributes constitute
     * overrides. Only differences in the group context are considered
     * overrides.
     */
    protected int countOverrides(SVGGraphicContext deltaGC) {
        return deltaGC.getGroupContext().size();
    }

    
Removes properties that do not apply for a specific element

/**
     * Removes properties that do not apply for a specific element
     */
    protected void trimContextForElement(SVGGraphicContext svgGC, Element element) {
        String tag = element.getTagName();
        Map groupAttrMap = svgGC.getGroupContext();
        if (tag != null) {
            // For each attribute, check if there is an attribute
            // descriptor. If there is, check if the attribute
            // applies to the input element. If there is none,
            // assume the attribute applies to the element.
            for (Object o : groupAttrMap.keySet()) {
                String attrName = (String) o;
                SVGAttribute attr = SVGAttributeMap.get(attrName);
                if (attr != null && !attr.appliesTo(tag))
                    groupAttrMap.remove(attrName);
            }
        }
    }

    
Processes the transform attribute value corresponding to a
given transform stack

/**
     * Processes the transform attribute value corresponding to a
     * given transform stack
     */
    protected void setTransform(Element element,
                              TransformStackElement[] transformStack) {
        String transform = domTreeManager.gcConverter.
            toSVG(transformStack).trim();
        if (transform.length() > 0)
            element.setAttributeNS(null, SVG_TRANSFORM_ATTRIBUTE, transform);
    }

    
Processes the difference between two graphic contexts. The values
in gc that are different from the values in referenceGc will be
present in the delta. Other values will no.

/**
     * Processes the difference between two graphic contexts. The values
     * in gc that are different from the values in referenceGc will be
     * present in the delta. Other values will no.
     */
    static SVGGraphicContext processDeltaGC(SVGGraphicContext gc,
                                            SVGGraphicContext referenceGc) {
        Map groupDelta = processDeltaMap(gc.getGroupContext(),
                                         referenceGc.getGroupContext());
        Map graphicElementDelta = gc.getGraphicElementContext();

        TransformStackElement[] gcTransformStack = gc.getTransformStack();
        TransformStackElement[] referenceStack = referenceGc.getTransformStack();
        int deltaStackLength = gcTransformStack.length - referenceStack.length;
        TransformStackElement[] deltaTransformStack =
            new TransformStackElement[deltaStackLength];

        System.arraycopy(gcTransformStack, referenceStack.length,
                         deltaTransformStack, 0, deltaStackLength);

        /**
           System.err.println("gc transform stack length: " +
           gc.getTransformStack().length);
           System.err.println("reference stack length   : " +
           referenceGc.getTransformStack().length);
           System.err.println("delta stack length       : " +
           deltaTransformStack.length);
        */

        /*
          TransformStackElement gcStack[] = gc.getTransformStack();
          for(int i=0; i<gcStack.length; i++)
          System.err.println("gcStack[" + i + "] = " + gcStack[i].toString());

          TransformStackElement refStack[] = referenceGc.getTransformStack();
          for(int i=0; i<refStack.length; i++)
          System.err.println("refStack[" + i + "] = " + refStack[i].toString());

          for(int i=0; i<deltaTransformStack.length; i++)
          System.err.println("deltaStack[" + i + "] = " +
          deltaTransformStack[i].toString());
        */

        SVGGraphicContext deltaGC = new SVGGraphicContext(groupDelta,
                                                          graphicElementDelta,
                                                          deltaTransformStack);

        return deltaGC;
    }

    
Processes the difference between two Maps. The code assumes
that the input Maps have the same key sets. Values in map that
are different from values in referenceMap are place in the
returned delta Map.

/**
     * Processes the difference between two Maps. The code assumes
     * that the input Maps have the same key sets. Values in map that
     * are different from values in referenceMap are place in the
     * returned delta Map.
     */
    static Map processDeltaMap(Map map, Map referenceMap) {
        // no need to be synch => HashMap
        Map mapDelta = new HashMap();
        for (Object o : map.keySet()) {
            String key = (String) o;
            String value = (String) map.get(key);
            String refValue = (String) referenceMap.get(key);
            if (!value.equals(refValue)) {
                /*if(key.equals(SVG_TRANSFORM_ATTRIBUTE)){
                  // Special handling for the transform attribute.
                  // At this point in the processing, the transform
                  // in map has to be a substring of the one in
                  // referenceMap. see the addElement member.
                  value = value.substring(refValue.length()).trim();
                  }*/
                mapDelta.put(key, value);
            }
        }
        return mapDelta;
    }
}