src/main/java/org/jfree/graphics2d/svg/SVGGraphics2D.java
private String getRadialGradientElement(String id, RadialGradientPaint rgp) {
        StringBuilder b = new StringBuilder("<radialGradient id=\"").append(id)
                .append("\" gradientUnits=\"userSpaceOnUse\" ");
        Point2D center = rgp.getCenterPoint();
        Point2D focus = rgp.getFocusPoint();
        float radius = rgp.getRadius();
        b.append("cx=\"").append(geomDP(center.getX())).append("\" ");
        b.append("cy=\"").append(geomDP(center.getY())).append("\" ");
        b.append("r=\"").append(geomDP(radius)).append("\" ");
        b.append("fx=\"").append(geomDP(focus.getX())).append("\" ");
        b.append("fy=\"").append(geomDP(focus.getY())).append("\">");
        
        Color[] colors = rgp.getColors();
        float[] fractions = rgp.getFractions();
        for (int i = 0; i < colors.length; i++) {
            Color c = colors[i];
            float f = fractions[i];
            b.append("<stop offset=\"").append(geomDP(f * 100)).append("%\" ");
            b.append("stop-color=\"").append(rgbColorStr(c)).append("\"");
            if (c.getAlpha() < 255) {
                double alphaPercent = c.getAlpha() / 255.0;
                b.append(" stop-opacity=\"").append(transformDP(alphaPercent))
                        .append("\"");                
            }            
            b.append("/>");
        }
        return b.append("</radialGradient>").toString();
    }
private String getRadialGradientElement(String id, RadialGradientPaint rgp) {
        StringBuilder b = new StringBuilder("<radialGradient id=\"").append(id)
                .append("\" gradientUnits=\"userSpaceOnUse\" ");
        Point2D center = rgp.getCenterPoint();
        Point2D focus = rgp.getFocusPoint();
        float radius = rgp.getRadius();
        b.append("cx=\"").append(geomDP(center.getX())).append("\" ");
        b.append("cy=\"").append(geomDP(center.getY())).append("\" ");
        b.append("r=\"").append(geomDP(radius)).append("\" ");
        b.append("fx=\"").append(geomDP(focus.getX())).append("\" ");
        b.append("fy=\"").append(geomDP(focus.getY())).append("\">");
        
        Color[] colors = rgp.getColors();
        float[] fractions = rgp.getFractions();
        for (int i = 0; i < colors.length; i++) {
            Color c = colors[i];
            float f = fractions[i];
            b.append("<stop offset=\"").append(geomDP(f * 100)).append("%\" ");
            b.append("stop-color=\"").append(rgbColorStr(c)).append("\"");
            if (c.getAlpha() < 255) {
                double alphaPercent = c.getAlpha() / 255.0;
                b.append(" stop-opacity=\"").append(transformDP(alphaPercent))
                        .append("\"");                
            }            
            b.append("/>");
        }
        return b.append("</radialGradient>").toString();
    }
Returns an element to represent a radial gradient.  All the radial
gradients that are used get written to the DEFS element in the SVG.

@param id  the reference id.
@param rgp  the radial gradient.

@return The SVG element.