http://xmlgraphics.apache.org/fop/: Apache FOP (Formatting Objects Processor) is the world's first print formatter driven by XSL formatting objects (XSL-FO) and the world's first output independent formatter. It is a Java application that reads a formatting object (FO) tree and renders the resulting pages to a specified output. Output formats currently supported include PDF, PCL, PS, AFP, TIFF, PNG, SVG, XML (area tree representation), Print, AWT and TXT. The primary output target is PDF. (Apache Software Foundation) 
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * 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.
 */

/* $Id$ */

package org.apache.fop.render.ps;

import java.util.List;

import org.apache.fop.render.gradient.Function;
import org.apache.fop.render.gradient.Function.SubFunctionRenderer;
import org.apache.fop.render.gradient.GradientMaker.DoubleFormatter;
import org.apache.fop.render.gradient.Pattern;
import org.apache.fop.render.gradient.Shading;


Helper class to draw gradients in PostScript.

/**
 * Helper class to draw gradients in PostScript.
 */
public final class Gradient {

    private Gradient() { }

    public static String outputPattern(Pattern pattern, DoubleFormatter doubleFormatter) {
        StringBuilder p = new StringBuilder(64);
        p.append("/Pattern setcolorspace\n");
        p.append("<< \n/Type /Pattern \n");

        p.append("/PatternType " + pattern.getPatternType() + " \n");

        if (pattern.getShading() != null) {
            p.append("/Shading ");
            outputShading(p, pattern.getShading(), doubleFormatter);
            p.append(" \n");
        }
        p.append(">> \n");
        List<Double> matrix = pattern.getMatrix();
        if (matrix == null) {
            p.append("matrix ");
        } else {
            p.append("[ ");
            for (double m : pattern.getMatrix()) {
                p.append(doubleFormatter.formatDouble(m));
                p.append(" ");
            }
            p.append("] ");
        }
        p.append("makepattern setcolor\n");

        return p.toString();
    }

    private static void outputShading(StringBuilder out, Shading shading, final DoubleFormatter doubleFormatter) {
        final Function function = shading.getFunction();
        Shading.FunctionRenderer functionRenderer = new Shading.FunctionRenderer() {

            public void outputFunction(StringBuilder out) {
                SubFunctionRenderer subFunctionRenderer = new Function.SubFunctionRenderer() {

                    public void outputFunction(StringBuilder out, int functionIndex) {
                        Function subFunction = function.getFunctions().get(functionIndex);
                        assert subFunction.getFunctions().isEmpty();
                        subFunction.output(out, doubleFormatter, null);
                    }
                };
                function.output(out, doubleFormatter, subFunctionRenderer);
            }
        };
        shading.output(out, doubleFormatter, functionRenderer);
    }

}