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<!-- author spei@cs.uiowa.edu                                                  -->
<!-- author cjolif@ilog.fr                                                     -->
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<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V2.0//EN" "http://forrest.apache.org/dtd/document-v20.dtd">
<document>
  <header>
    <title>SVG Generator: SVGGraphics2D</title>
  </header>

  <body>
    <div class="figure"><img src="images/svggen.jpg" alt="Flow diagram illustrating that Java programs can have their graphics converted to SVG and then viewed in any SVG viewer"/>
    </div>
    <p>
      As SVG is emerging as a promising graphics format for a wide range of
      domains and applications, bridging it with Java becomes important.  This
      page explains how Batik’s
      <a class="class" href="../javadoc/org/apache/batik/svggen/SVGGraphics2D.html">SVGGraphics2D</a>,
      referred to as the SVG Generator, makes this possible.
    </p>

    <section id="whatIsIt">
      <title>The <code>SVGGraphics2D</code> class</title>
      <p>
        On the Java platform, all rendering goes through the
        <a class="class" href="http://java.sun.com/j2se/1.5.0/docs/api/java/awt/Graphics2D.html">Graphics2D</a>
        abstract class, which offers methods such as <code>drawRect</code>,
        <code>fillRect</code>, and <code>drawString</code>. There are
        specialized implementations of this abstract class for each type of
        output, such as a screen or a printer.  <code>SVGGraphics2D</code> is
        a new implementation of that interface that generates SVG content
        instead of drawing to a screen or a printer.
      </p>

      <p>
        <code>SVGGraphics2D</code> has the following features:
      </p>
      <ul>        
        <li>
          it allows applications to export their graphics into SVG format,
        </li>
        <li>
          it does not require any modification of the graphics code to export
          to SVG, and
        </li>
        <li>
          it offers the user the ability to use the DOM API to manipulate the
          generated document.
        </li>
      </ul>

      <div class="figure"><img src="images/svggenHighLevelArchi.jpg" alt="Diagram illustrating how the SVGGraphics2D inherits from Graphics2D, and uses Document to generate a DOM tree"/>
      </div>

      <p>
        The above figure shows how the generator works with the DOM API. The W3C
        has defined an API for representing XML content with a Java object.
        That API allows programmers to manipulate, create, and/or modify XML
        content in memory. The DOM API contains interfaces such as
        <a class="class" href="http://java.sun.com/j2se/1.5.0/docs/api/org/w3c/dom/Document.html">Document</a>,
        <a class="class" href="http://java.sun.com/j2se/1.5.0/docs/api/org/w3c/dom/Element.html">Element</a>,
        and
        <a class="class" href="http://java.sun.com/j2se/1.5.0/docs/api/org/w3c/dom/Attr.html">Attr</a>,
        which model the Java programming language equivalent of XML documents,
        elements and attributes. 
      </p>
      <p>
        The generator manages a tree of DOM objects that represent the SVG
        content corresponding to the rendering calls made on the
        <code>SVGGraphics2D</code> instance. In other words, every time a
        program invokes a rendering method, such as <code>fillRect</code>, on a
        <code>SVGGraphics2D</code> instance, a new DOM object,
        representing the SVG equivalent, is appended to the DOM tree.  For
        example, a <code>rect</code> element will be appended after the
        <code>fillRect</code> method has been invoked). 
      </p>
      <p>
        The programmer, using this generator, can then access the DOM tree to
        further manipulate it or can directly write the content to an output
        stream, as we see in the following section. 
      </p>

    </section>

    <section id="howToUse">
      <title>How to use SVGGraphics2D</title>
      <p>
        From the figure in the previous section we can see that in order for an
        instance of <code>SVGGraphics2D</code> to build the SVG content (the
        DOM tree), an instance of a <code>Document</code> class is needed. The
        DOM tree is an in-memory representation of the SVG document, which can
        be further manipulated by the user using DOM API or be streamed
        out by a
        <a class="class" href="http://java.sun.com/j2se/1.5.0/docs/api/java/io/Writer.html">Writer</a>
        object.
      </p>

      <p>
        The following example program demonstrates how to generate SVG content
        from Java graphics.
      </p>

      <source><![CDATA[import java.awt.Rectangle;
import java.awt.Graphics2D;
import java.awt.Color;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.io.IOException;

import org.apache.batik.svggen.SVGGraphics2D;
import org.apache.batik.dom.GenericDOMImplementation;

import org.w3c.dom.Document;
import org.w3c.dom.DOMImplementation;

public class TestSVGGen {

    public void paint(Graphics2D g2d) {
        g2d.setPaint(Color.red);
        g2d.fill(new Rectangle(10, 10, 100, 100));
    }

    public static void main(String[] args) throws IOException {

        // Get a DOMImplementation.
        DOMImplementation domImpl =
            GenericDOMImplementation.getDOMImplementation();

        // Create an instance of org.w3c.dom.Document.
        String svgNS = "http://www.w3.org/2000/svg";
        Document document = domImpl.createDocument(svgNS, "svg", null);

        // Create an instance of the SVG Generator.
        SVGGraphics2D svgGenerator = new SVGGraphics2D(document);

        // Ask the test to render into the SVG Graphics2D implementation.
        TestSVGGen test = new TestSVGGen();
        test.paint(svgGenerator);

        // Finally, stream out SVG to the standard output using
        // UTF-8 encoding.
        boolean useCSS = true; // we want to use CSS style attributes
        Writer out = new OutputStreamWriter(System.out, "UTF-8");
        svgGenerator.stream(out, useCSS);
    }
}]]></source>

      <p>
        We can see that generating SVG content from our <code>TestSVGGen</code>
        instance is a three step process:
      </p>
      <ol>
        <li>
          <p>
            Create an instance of <code>org.w3c.dom.Document</code> that the
            generator will use to build its XML content, and create an SVG generator
            using the <code>Document</code> instance.
          </p>
          <source>        // Get a DOMImplementation.
        DOMImplementation domImpl =
            GenericDOMImplementation.getDOMImplementation();

        // Create an instance of org.w3c.dom.Document.
        String svgNS = "http://www.w3.org/2000/svg";
        Document document = domImpl.createDocument(svgNS, "svg", null);

        // Create an instance of the SVG Generator.
        SVGGraphics2D svgGenerator = new SVGGraphics2D(document);</source>
        </li>
        <li>
          <p>
            Invoke the rendering code on our SVG generator. In our example, we
            invoke <code>TestSVGGen</code>‘s <code>paint</code> method:
          </p>
          <source>        // Ask the test to render into the SVG Graphics2D implementation.
        TestSVGGen test = new TestSVGGen();
        test.paint(svgGenerator);</source>
        </li>
        <li>
          <p>
            Stream out the SVG content. The SVG generator can stream its content
            into any <code>java.io.Writer</code>. In our example, we stream the
            content to the standard output stream:
          </p>
          <source>        // Finally, stream out SVG to the standard output using
        // UTF-8 encoding.
        boolean useCSS = true; // we want to use CSS style attributes
        Writer out = new OutputStreamWriter(System.out, "UTF-8");
        svgGenerator.stream(out, useCSS);</source>
        </li>
      </ol>
      <p>
        SVG has
        <a href="http://www.w3.org/TR/SVG11/styling.html#AlternativesForStyling">two
          ways to specify styling properties</a>, such as the fill color:
        presentation attributes (one XML attribute per property) or the CSS
        <code>style</code> attribute (any number of properties in one CSS
        inline stylesheet).  The <code>useCss</code> parameter allows the user
        to control that option. 
      </p>
    </section>

    <section id="custom">
      <title>SVG Generator customization</title>
      <p>
        In the previous section, we have just seen that the SVG generation
        process can be customized to output SVG styling properties as 
        presentation attributes or CSS inline stylesheets.  In this section we
        will talk about some examples of more advanced customizations.
      </p>
      <p>
        Instead of creating the <code>SVGGraphics2D</code> just by using the
        <code>Document</code> that will be used as a factory for creating the
        SVG elements, we can use the constructor that uses an
        <a class="class" href="../javadoc/org/apache/batik/svggen/SVGGeneratorContext.html">SVGGeneratorContext</a>
        instance. By providing your own <code>SVGGeneratorContext</code>
        instance, you will be able to do advanced customization. You will find
        below several examples of possible customizations.
      </p>
      <section>
        <title>Have your own comment in the generated SVG file</title>
        <p>
          We begin with the simplest possible example. If you integrate the
          Batik SVG generator in your own Java application, you may want to
          specialize the comment generated in the XML code.
        </p>

        <source>DOMImplementation impl =
    GenericDOMImplementation.getDOMImplementation();
String svgNS = "http://www.w3.org/2000/svg";
Document myFactory = impl.createDocument(svgNS, "svg", null);

SVGGeneratorContext ctx = SVGGeneratorContext.createDefault(myFactory);
<strong>ctx.setComment("Generated by FooApplication with Batik SVG Generator");</strong>
SVGGraphics2D g2d = new SVGGraphics2D(ctx, false);</source>
      </section>

      <section>
        <title>Use embedded SVG Fonts in the generated SVG file</title>
        <p>
          In order to have a self-contained SVG file that doesn't have to use
          system fonts to be displayed, you can embed the fonts you used for
          drawing strings in the SVG file through the SVG fonts facility.
        </p>

        <source>DOMImplementation impl =
    GenericDOMImplementation.getDOMImplementation();
String svgNS = "http://www.w3.org/2000/svg";
Document myFactory = impl.createDocument(svgNS, "svg", null);

SVGGeneratorContext ctx = SVGGeneratorContext.createDefault(myFactory);
<strong>ctx.setEmbeddedFontsOn(true);</strong>
SVGGraphics2D g2d = new SVGGraphics2D(ctx, <strong>true</strong>);</source>
      </section>

      <section>
        <title>Customizing the way images are stored</title>
        <p>
          Every time you call one of the <code>drawImage</code> methods
          provided by the <code>Graphics2D</code> interface, a default
          representation of your image is created in a location and put in a
          default file. For instance, a base64 encoding is created and embedded
          in the SVG file by default. Alternatively, you can choose to have your
          images written to separate files in a predefined directory, in one of
          the two raster formats required by the SVG specification: JPEG or PNG.
        </p>
        <p>
          You can change the default behavior by explicitly providing the
          image handler to be used by the SVG generator.  Once again, you use
          the <code>SVGGeneratorContext</code> for this. In the example below,
          all images are converted to PNG format and written to directory
          <code>res/images</code>.
        </p>
        <source>DOMImplementation impl =
    GenericDOMImplementation.getDOMImplementation();
String svgNS = "http://www.w3.org/2000/svg";
Document myFactory = impl.createDocument(svgNS, "svg", null);

SVGGeneratorContext ctx = SVGGeneratorContext.createDefault(myFactory);
<strong>GenericImageHandler ihandler = new ImageHandlerPNGEncoder("res/images", null);
ctx.setImageHandler(ihandler);</strong>
SVGGraphics2D g2d = new SVGGraphics2D(ctx, false);</source>
        <p>
          Using the default image handlers results in a new copy of the image
          data being written to the SVG file or an external file, for every
          single <code>drawImage</code> call. If you use the same images over
          and over again, then this may result in an SVG file containing a lot
          of redundant data. At the price of a slight performance penalty
          during initial generation of the SVG DOM tree, you can choose to
          have your image data reused. For this you use a specialized image
          handler, as shown below.
        </p>
        <source>DOMImplementation impl =
    GenericDOMImplementation.getDOMImplementation();
String svgNS = "http://www.w3.org/2000/svg";
Document myFactory = impl.createDocument(svgNS, "svg", null);

SVGGeneratorContext ctx = SVGGeneratorContext.createDefault(myFactory);

// Reuse our embedded base64-encoded image data.
<strong>GenericImageHandler ihandler = new CachedImageHandlerBase64Encoder();
ctx.setGenericImageHandler(ihandler);</strong>

SVGGraphics2D g2d = new SVGGraphics2D(ctx, false);</source>
        <p>
          With the caching image handlers, it is even possible to reuse the
          same copy of your image data across several different SVG documents.
          Just keep a reference to the image handler, and pass it to the
          <code>SVGGraphics2D</code> instance used for generating the SVG DOM
          tree. The following simplified example shows how different SVG trees
          might be created by separate SVG generators, efficiently storing any
          common images just once.
        </p>
        <source>class MySVGGenerator {

    // The image handler will write all images files to "res/images".
<strong>    private static ImageHandler ihandler =
        new CachedImageHandlerPNGEncoder("res/images", null);</strong>

    public void generateSVG(JPanel myCanvas, OutputStream outStream) {
        DOMImplementation domImpl =
            GenericDOMImplementation.getDOMImplementation();
        Document myFactory = domImpl.createDocument(svgNS, "svg", null);
        SVGGeneratorContext ctx =
            SVGGeneratorContext.createDefault(myFactory);
        <strong>ctx.setGenericImageHandler(ihandler);</strong>

        SVGGraphics2D svgGenerator = new SVGGraphics2D(ctx, false);

        // Create the SVG DOM tree.
        myCanvas.paintComponent(svgGenerator);

        Writer out = new OutputStreamWriter(outStream, "UTF-8");
        svgGenerator.stream(out, true);
    }
}</source>

      </section>

      <section>
        <title>Customizing the generated SVG style</title>
        <p>
          Your needs in matter of styling may be different from the two
          provided options (XML presentation attributes or CSS inline
          stylesheets). For example, you may want to put the CSS properties in
          a SVG <code>style</code> element section and reference them through
          the class attribute.  In this case you will need to define a new
          <a class="class" href="../javadoc/org/apache/batik/svggen/StyleHandler.html">StyleHandler</a>
          as below.
        </p>
        <source>public class StyleSheetStyleHandler implements StyleHandler {

    // The CDATA section that holds the CSS stylesheet.
    private CDATASection styleSheet;

    // Build the handler with a reference to the stylesheet section.
    public StyleSheetStyleHandler(CDATASection styleSheet) {
        this.styleSheet = styleSheet;
    }

    public void setStyle(Element element, Map styleMap,
                         SVGGeneratorContext generatorContext) {
        Iterator iter = styleMap.keySet().iterator();

        // Create a new class in the style sheet.
        String id = generatorContext.getIDGenerator().generateID("C");
        styleSheet.appendData("."+ id +" {");

        // Append each key/value pair.
        while (iter.hasNext()) {
            String key = (String) iter.next();
            String value = (String) styleMap.get(key);
            styleSheet.appendData(key + ":" + value + ";");
        }

        styleSheet.appendData("}\n");

        // Reference the stylesheet class on the element to be styled.
        element.setAttributeNS(null, "class", id);
    }
}</source>
        <p>
          Then you can create and use an <code>SVGGraphics2D</code> with a
          correctly configured <code>SVGGeneratorContext</code>.
        </p>
        <source>
// Configure the SVGGraphics2D for a given Document myFactory.
SVGGeneratorContext ctx = SVGGeneratorContext.createDefault(myFactory);
CDATASection styleSheet = myFactory.createCDATASection("");
ctx.setStyleHandler(new StyleSheetStyleHandler(styleSheet));
SVGGraphics2D g2d = new SVGGraphics2D(ctx, false);

// Use the g2d to draw (e.g., component.paint(g2d)).

// Add a stylesheet to the definition section.
SVGSVGElement root = (SVGSVGElement) g2d.getRoot();
Element defs = root.getElementById(SVGSyntax.ID_PREFIX_GENERIC_DEFS);
Element style = myFactory.createElementNS
    (SVGSyntax.SVG_NAMESPACE_URI, SVGSyntax.SVG_STYLE_TAG);
style.setAttributeNS(null, SVGSyntax.SVG_TYPE_ATTRIBUTE, "text/css");
style.appendChild(styleSheet);
defs.appendChild(style);

// Dump the root content to a given Writer myWriter.
g2d.stream(root, myWriter);</source>
      </section>

      <section>
        <title>Extending Paint object to SVG element translation</title>
        <p>
          The <code>SVGGraphics2D</code> is able to generate SVG elements for
          generic Java 2D objects, but you sometimes have your own classes such
          as implementations of the Java 2D
          <a class="class" href="http://java.sun.com/j2se/1.4.2/docs/api/java/awt/Paint.html">Paint</a>
          interface. In this case, you will need to write an
          <a class="class" href="../javadoc/org/apache/batik/svggen/ExtensionHandler.html">ExtensionHandler</a>
          that you will set on your <code>SVGGeneratorContext</code>.
        </p>
        <p>
          In the following example we define the first draft of an
          <code>ExtensionHandler</code> allowing to translate a Batik
          implementation of the <code>Paint</code> interface named
          <a class="class" href="../javadoc/org/apache/batik/ext/awt/LinearGradientPaint.html">LinearGradientPaint</a>. 
        </p>
        <source>class MyExtensionHandler extends DefaultExtensionHandler {

    public SVGPaintDescriptor handlePaint(Paint paint,
                                          SVGGeneratorContext generatorCtx) {
        if (paint instanceof LinearGradientPaint) {
            LinearGradientPaint gradient = (LinearGradientPaint) paint;

            // Create a new SVG 'linearGradient' element to represent the
            // LinearGradientPaint being used.
            String id = generatorCtx.getIDGenerator().generateID("gradient");
            Document doc = generatorCtx.getDOMFactory();
            Element grad = doc.createElementNS
                (SVGSyntax.SVG_NAMESPACE_URI,
                 SVGSyntax.SVG_LINEAR_GRADIENT_TAG);

            // Set the relevant attributes on the 'linearGradient' element.
            grad.setAttributeNS(null, SVGSyntax.SVG_ID_ATTRIBUTE, id);
            grad.setAttributeNS(null, SVGSyntax.SVG_GRADIENT_UNITS_ATTRIBUTE,
                                SVGSyntax.SVG_USER_SPACE_ON_USE_VALUE);
            Point2D pt = gradient.getStartPoint();
            grad.setAttributeNS(null, "x1", pt.getX());
            grad.setAttributeNS(null, "y1", pt.getY());
            pt = gradient.getEndPoint();
            grad.setAttributeNS(null, "x2", pt.getX());
            grad.setAttributeNS(null, "y2", pt.getY());

            switch (gradient.getCycleMethod()) {
            case MultipleGradientPaint.REFLECT:
                grad.setAttributeNS
                    (null, SVGSyntax.SVG_SPREAD_METHOD_ATTRIBUTE,
                     SVGSyntax.SVG_REFLECT_VALUE);
                break;
            case MultipleGradientPaint.REPEAT:
                grad.setAttributeNS
                    (null, SVGSyntax.SVG_SPREAD_METHOD_ATTRIBUTE,
                     SVGSyntax.SVG_REPEAT_VALUE);
                break;
            // 'pad' is the default...
            }

            // Here we should write the transform of the gradient
            // in the transform attribute...

            // Here we should write the stops of the gradients as 
            // children elements...

            return new SVGPaintDescriptor
                ("url(#" + ref + ")", SVGSyntax.SVG_OPAQUE_VALUE, grad);
        } else {
            // Let the default mechanism do its job.
            return null;
        }
    }
}</source>
        <p>
          You should then set it on the <code>SVGGeneratorContext</code> by
          using the <code>setExtensionHandler</code> method.
        </p>
        <source>SVGGeneratorContext ctx = SVGGeneratorContext.createDefault(myFactory);
ctx.setExtensionHandler(new MyExtensionHandler());
SVGGraphics2D g2d = new SVGGraphics2D(ctx, false);</source>
      </section>
    </section>

    <section id="view">
      <title>How to view the generated SVG document</title>

      <p>
        The following code example illustrates how to view the SVG content
        generated
        by an <code>SVGGraphics2D</code> object.</p>

      <source>import java.awt.*;
import java.awt.geom.*;

import javax.swing.*;

import org.apache.batik.swing.*;
import org.apache.batik.svggen.*;
import org.apache.batik.dom.svg.SVGDOMImplementation;

import org.w3c.dom.*;
import org.w3c.dom.svg.*;

public class ViewGeneratedSVGDemo {

    public static void main(String[] args) {
        // Create an SVG document.
        DOMImplementation impl = SVGDOMImplementation.getDOMImplementation();
        String svgNS = SVGDOMImplementation.SVG_NAMESPACE_URI;
        SVGDocument doc = (SVGDocument) impl.createDocument(svgNS, "svg", null);

        // Create a converter for this document.
        SVGGraphics2D g = new SVGGraphics2D(doc);

        // Do some drawing.
        Shape circle = new Ellipse2D.Double(0, 0, 50, 50);
        g.setPaint(Color.red);
        g.fill(circle);
        g.translate(60, 0);
        g.setPaint(Color.green);
        g.fill(circle);
        g.translate(60, 0);
        g.setPaint(Color.blue);
        g.fill(circle);
        g.setSVGCanvasSize(new Dimension(180, 50));

        // Populate the document root with the generated SVG content.
        Element root = doc.getDocumentElement();
        g.getRoot(root);

        // Display the document.
        JSVGCanvas canvas = new JSVGCanvas();
        JFrame f = new JFrame();
        f.getContentPane().add(canvas);
        canvas.setSVGDocument(doc);
        f.pack();
        f.setVisible(true);
    }
}</source>
    </section>
  </body>
</document>
