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| <!-- author spei@cs.uiowa.edu --> |
| <!-- author cjolif@ilog.fr --> |
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| <!-- ========================================================================= --> |
| <document> |
| <header> |
| <title>SVGGraphics2D</title> |
| <subtitle>A brief of the SVG Generator in Java(SVGGraphics2D)</subtitle> |
| <authors> |
| <person name="Sheng Pei" email="spei@cs.uiowa.edu"/> |
| <person name="Vincent Hardy" email="vincent.hardy@eng.sun.com"/> |
| <person name="Christophe Jolif" email="cjolif@ilog.fr"/> |
| </authors> |
| </header> |
| |
| <body> |
| <s1 title="Introduction"> |
| |
| <figure src="images/svggen.jpg" alt="Batik SVG Generator"/> |
| <p> |
| As SVG(Scalable Vector Graphics) 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 <code>SVGGraphics2D</code>, referred to as the SVG Generator, makes |
| this possible. It is divided into three parts: </p> |
| <ul> |
| <li><link href="#whatIsIt">What is <code>SVGGraphics2D</code>?</link></li> |
| <li><link href="#howToUse">How to use <code>SVGGraphics2D</code>?</link></li> |
| <li><link href="#custom">How to customize SVG Generation process?</link></li> |
| </ul> |
| |
| </s1> |
| |
| <anchor id="whatIsIt" /> |
| <s1 title="What's SVGGraphics2D"> |
| <p> |
| On the Java platform, all rendering goes through the <code>java.awt.Graphics2D</code> |
| abstract class, which offers methods such as <code>drawRect</code>, <code>fillRect</code>, or |
| <code>drawString</code>. There are specialized |
| implementations of this abstract class for each type of output, such as a monitor 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> provides the following: |
| </p> |
| <ul> |
| <li> Allows applications to export their graphics into SVG format. </li> |
| <li> Does not require any modification of the graphics code to export to SVG. </li> |
| <li> Offers the user the ability to use the DOM API to manipulate the generated document. </li> |
| </ul> |
| <figure src="images/svggenHighLevelArchi.jpg" alt="High level architecture" /> |
| |
| <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 programming language object. That API allows programmers to manipulate, create, |
| and/or modify XML content in memory. The DOM API contains interfaces such as <code>Document</code>, |
| <code>Element</code>, and <code>Attr</code>, |
| 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 <rect> 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> |
| |
| </s1> |
| |
| <anchor id="howToUse" /> |
| <s1 title="How to use SVGGraphics2D"> |
| <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 DOM's <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 into any <code>java.io.Writer</code>. |
| </p> |
| |
| <p> |
| The following excerpted code example shows how to generate SVG content from Java graphics. |
| </p> |
| <source> |
| |
| 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 |
| Document document = domImpl.createDocument(null, "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 |
| // character to byte encoding |
| boolean useCSS = true; // we want to use CSS style attribute |
| 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> |
| <p> |
| 1. Create an instance of <code>org.w3c.dom.Document</code> that the generator will use to build its XML content; |
| create a 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 |
| Document document = domImpl.createDocument(null, "svg", null); |
| |
| // Create an instance of the SVG Generator |
| SVGGraphics2D svgGenerator = new SVGGraphics2D(document); |
| </source> |
| <p> |
| 2. 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> |
| <p> |
| 3. 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 |
| // character to byte encoding |
| boolean useCSS = true; // we want to use CSS style attribute |
| Writer out = new OutputStreamWriter(System.out, "UTF-8"); |
| svgGenerator.stream(out, useCSS); |
| </source> |
| <p> |
| SVG has two ways of expressing properties, such as the fill color: either XML attributes or CSS inline properties. |
| The 'useCss' parameter allows the user to control that option. |
| </p> |
| </s1> |
| <anchor id="custom" /> |
| <s1 title="SVG Generator Customization"> |
| <p> |
| In the previous section, we have just seen that the SVG generation process can be customized to output SVG style as XML attributes or CSS inline properties. 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 use an <code>SVGGeneratorContext</code> 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> |
| <s2 title="Have your own comment in the generated SVG file"> |
| <p> |
| We begin with the simpliest 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. You can proceed as below. |
| </p> |
| <source> |
| |
| SVGGeneratorContext ctx = SVGGeneratorContext.createDefault(myFactory); |
| ctx.setComment("Generated by FooApplication with Batik SVG Generator"); |
| SVGGraphics2D g2d = new SVGGraphics2D(ctx); |
| </source> |
| |
| </s2> |
| <s2 title="Use Embedded SVG Fonts in the generated SVG file"> |
| <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> |
| |
| SVGGeneratorContext ctx = SVGGeneratorContext.createDefault(myFactory); |
| ctx.setEmbeddedFontsOn(true); |
| SVGGraphics2D g2d = new SVGGraphics2D(ctx); |
| </source> |
| |
| </s2> |
| |
| <s2 title="Customizing the generated SVG style"> |
| <p> |
| Your needs in matter of styling may be different from the two provided options (XML attributes or CSS inline properties). For example you may want to put the CSS properties in a stylesheet SVG element section and reference them through the class attribute. In this case you will need to define a new <code>StyleHandler</code> as below. |
| </p> |
| <source> |
| |
| public class StyleSheetStyleHandler { |
| 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 id in the style sheet |
| String id = generatorContext.getIDGenerator().generateID("C"); |
| styleSheet.appendData("."+id+" {"); |
| // append each key/value pairs |
| while (iter.hasNext()) { |
| String key = (String)iter.next(); |
| String value = (String)styleMap.get(key); |
| styleSheet.appendData(key+":"+value+";"); |
| } |
| styleSheet.appendData("}\n"); |
| // reference the class id of the style sheet on the element to |
| // be styled |
| element.setAttribute("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); |
| |
| // use the g2d to dump drawings (component.paint(g2d)) |
| |
| // add a style sheet to the definition section |
| Element root = 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> |
| </s2> |
| <s2 title="Extending Paint object to SVG element translation"> |
| <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 <code>java.awt.Paint</code> interface. In this case, you will need to write an <code>ExtensionHandler</code> 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>java.awt.Paint</code> interface named <code>org.apache.batik.ext.awt.LinearGradientPaint</code>. |
| </p> |
| <source> |
| class SubExtensionHandler extends DefaultExtensionHandler |
| { |
| public SVGPaintDescriptor handlePaint(Paint paint, |
| SVGGeneratorContext generatorCtx) |
| { |
| if (paint instanceof LinearGradientPaint) { |
| LinearGradientPaint gradient = (LinearGradientPaint)paint; |
| String id = generatorCtx.getIDGenerator().generateID("gradient"); |
| Element grad = generatorCtx.getDOMFactory(). |
| createElementNS(SVGSyntax.SVG_NAMESPACE_URI, |
| SVGSyntax.SVG_LINEAR_GRADIENT_TAG); |
| grad.setAttributeNS(null, SVGSyntax.SVG_ID_ATTRIBUTE, ref); |
| 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 |
| return null; // let the default mechanism do its job |
| } |
| } |
| |
| </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 SubExtensionHandler()); |
| SVGGraphics2D g2d = new SVGGraphics2D(ctx);</source> |
| </s2> |
| </s1> |
| </body> |
| </document> |
