An ExtensionHandler for Apache Batik's svggen part that uses SVGGraphics2D to convert Swing drawing routines to SVG elements. Currently supports LinearGradientPaint and RadialGradientPaint. Feel free to comment and extend ..

GradientExtensionHandler.java

import static org.apache.batik.util.SVGConstants.*;

import java.awt.Color;
import java.awt.LinearGradientPaint;
import java.awt.MultipleGradientPaint;
import java.awt.Paint;
import java.awt.RadialGradientPaint;
import java.awt.geom.AffineTransform;
import java.awt.geom.Point2D;

import org.apache.batik.svggen.DefaultExtensionHandler;
import org.apache.batik.svggen.SVGColor;
import org.apache.batik.svggen.SVGGeneratorContext;
import org.apache.batik.svggen.SVGPaintDescriptor;
import org.w3c.dom.Element;

/**
 * Extension of Batik's {@link DefaultExtensionHandler} which 
 * handles different kinds of Paint objects
 * 
 * I wonder why this is not part of the svggen library.
 * @author Martin Steiger
 */
public class GradientExtensionHandler extends DefaultExtensionHandler
{
  @Override
	public SVGPaintDescriptor handlePaint(Paint paint, SVGGeneratorContext genCtx)
	{
		// Handle LinearGradientPaint
		if (paint instanceof LinearGradientPaint)
			return getLgpDescriptor((LinearGradientPaint) paint, genCtx);
			
		// Handle RadialGradientPaint
		if (paint instanceof RadialGradientPaint)
			return getRgpDescriptor((RadialGradientPaint) paint, genCtx);
		
		return super.handlePaint(paint, genCtx);
	}

	private SVGPaintDescriptor getRgpDescriptor(RadialGradientPaint gradient, SVGGeneratorContext genCtx)
	{
		Element gradElem = genCtx.getDOMFactory().createElementNS(SVG_NAMESPACE_URI, SVG_RADIAL_GRADIENT_TAG);

		// Create and set unique XML id
		String id = genCtx.getIDGenerator().generateID("gradient");
		gradElem.setAttribute(SVG_ID_ATTRIBUTE, id);

		// Set x,y pairs
		Point2D centerPt = gradient.getCenterPoint();
		gradElem.setAttribute("cx", String.valueOf(centerPt.getX()));
		gradElem.setAttribute("cy", String.valueOf(centerPt.getY()));

		Point2D focusPt = gradient.getFocusPoint();
		gradElem.setAttribute("fx", String.valueOf(focusPt.getX()));
		gradElem.setAttribute("fy", String.valueOf(focusPt.getY()));

		gradElem.setAttribute("r", String.valueOf(gradient.getRadius()));

		addMgpAttributes(gradElem, genCtx, gradient);

		return new SVGPaintDescriptor("url(#" + id + ")", SVG_OPAQUE_VALUE, gradElem);
	}
	
	private SVGPaintDescriptor getLgpDescriptor(LinearGradientPaint gradient, SVGGeneratorContext genCtx)
	{
		Element gradElem = genCtx.getDOMFactory().createElementNS(SVG_NAMESPACE_URI, SVG_LINEAR_GRADIENT_TAG);

		// Create and set unique XML id
		String id = genCtx.getIDGenerator().generateID("gradient");
		gradElem.setAttribute(SVG_ID_ATTRIBUTE, id);

		// Set x,y pairs
		Point2D startPt = gradient.getStartPoint();
		gradElem.setAttribute("x1", String.valueOf(startPt.getX()));
		gradElem.setAttribute("y1", String.valueOf(startPt.getY()));

		Point2D endPt = gradient.getEndPoint();
		gradElem.setAttribute("x2", String.valueOf(endPt.getX()));
		gradElem.setAttribute("y2", String.valueOf(endPt.getY()));

		addMgpAttributes(gradElem, genCtx, gradient);

		return new SVGPaintDescriptor("url(#" + id + ")", SVG_OPAQUE_VALUE, gradElem);
	}
	
	private void addMgpAttributes(Element gradElem, SVGGeneratorContext genCtx, MultipleGradientPaint gradient)
	{
		gradElem.setAttribute(SVG_GRADIENT_UNITS_ATTRIBUTE, SVG_USER_SPACE_ON_USE_VALUE);

		// Set cycle method
		switch (gradient.getCycleMethod())
		{
		case REFLECT:
			gradElem.setAttribute(SVG_SPREAD_METHOD_ATTRIBUTE, SVG_REFLECT_VALUE);
			break;
		case REPEAT:
			gradElem.setAttribute(SVG_SPREAD_METHOD_ATTRIBUTE, SVG_REPEAT_VALUE);
			break;
		case NO_CYCLE:
			gradElem.setAttribute(SVG_SPREAD_METHOD_ATTRIBUTE, SVG_PAD_VALUE);	// this is the default
			break;
		}

		// Set color space
		switch (gradient.getColorSpace())
		{
		case LINEAR_RGB:
			gradElem.setAttribute(SVG_COLOR_INTERPOLATION_ATTRIBUTE, SVG_LINEAR_RGB_VALUE);
			break;
			
		case SRGB:
			gradElem.setAttribute(SVG_COLOR_INTERPOLATION_ATTRIBUTE, SVG_SRGB_VALUE);
			break;
		}

		// Set transform matrix if not identity
		AffineTransform tf = gradient.getTransform();
		if (!tf.isIdentity())
		{
			String matrix = "matrix(" + 
					tf.getScaleX() + " " + tf.getShearX() + " " + tf.getTranslateX() + " " + 
					tf.getScaleY() + " " + tf.getShearY() + " " + tf.getTranslateY() + ")";
			gradElem.setAttribute(SVG_TRANSFORM_ATTRIBUTE, matrix);
		}

		// Convert gradient stops
		Color[] colors = gradient.getColors();
		float[] fracs = gradient.getFractions();
		
		for (int i = 0; i < colors.length; i++)
		{
			Element stop = genCtx.getDOMFactory().createElementNS(SVG_NAMESPACE_URI, SVG_STOP_TAG);
			SVGPaintDescriptor pd = SVGColor.toSVG(colors[i], genCtx);

			stop.setAttribute(SVG_OFFSET_ATTRIBUTE, (int) (fracs[i] * 100.0f) + "%");
			stop.setAttribute(SVG_STOP_COLOR_ATTRIBUTE, pd.getPaintValue());

			if (colors[i].getAlpha() != 255)
			{
				stop.setAttribute(SVG_STOP_OPACITY_ATTRIBUTE, pd.getOpacityValue());
			}
			
			gradElem.appendChild(stop);
		}		
	}	
}

hello Martin,

I find your batik ExtensionHandler for java.awt.(Linear|Radial)GradientPaint very useful, as I am part of the
freeplane project where we render SVGs using svgSalamander which generates these "Multiple" GradientPaints.

Setting your "GradientExtensionHandler" as an ExtensionHandler does improve things
(better color rendering), but gradients are still not rendered completely.

Here is a simple example (including use of "GradientExtensionHandler"):
https://github.com/fnatter/svgtest

In order to test this, please do:

• clone
• gradle build cleanEclipse eclipse
• import project into eclipse
• Start org.freeplane.svgtest.TestBatik
• choose a file to save the PDF to
• notice that gradient rendering is incomplete in the PDF

Could you help me fix this?

Many Thanks and Best Regards,
Felix

hello Martin,

I fixed my problem with this change in the transform (transform->gradientTransform, change order of parameters):
fnatter/svgtest@bb5b87a

Could you review this?

Cheers and Best Regards,
Felix

hi Martin,

with the above change it seems to work fine :-)
Can I use this code in the Freeplane project under the GPL (or less restrictive, like Apache/Mozilla/...) conditions?

Cheers and Best Regards,
Felix

Hello, sorry, I didn't see your comments until now. You can use the code under the MIT license if it is still relevant for you.