# CubicBezierCurve.java

    /*
     * Copyright 2014 The Apache Software Foundation.
     *
     * Licensed 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.
     */
    package org.apache.pdfbox.pdmodel.graphics.shading;

    import java.awt.geom.Point2D;

    /**
     * This class is used to describe the edge of each patch for type 6 shading.
     * This was done as part of GSoC2014, Tilman Hausherr is the mentor.
     *
     * @author Shaola Ren
     */
    class CubicBezierCurve
    {
        private final Point2D[] controlPoints;
        private final int level;
        private final Point2D[] curve;

        /**
         * Constructor of CubicBezierCurve
         *
         * @param ctrlPnts 4 control points [p0, p1, p2, p3]
         * @param l dividing level, if l = 0, one cubic Bezier curve is divided
         * into 2^0 = 1 segments, if l = n, one cubic Bezier curve is divided into
         * 2^n segments
         */
        CubicBezierCurve(Point2D[] ctrlPnts, int l)
        {
            controlPoints = ctrlPnts.clone();
            level = l;
            curve = getPoints(level);
        }

        /**
         * Get level parameter
         *
         * @return level
         */
        int getLevel()
        {
            return level;
        }

        // calculate sampled points on the cubic Bezier curve defined by the 4 given control points
        private Point2D[] getPoints(int l)
        {
            if (l < 0)
            {
                l = 0;
            }
            int sz = (1 << l) + 1;
            Point2D[] res = new Point2D[sz];
            double step = (double) 1 / (sz - 1);
            double t = -step;
            for (int i = 0; i < sz; i++)
            {
                t += step;
                double tmpX = (1 - t) * (1 - t) * (1 - t) * controlPoints[0].getX()
                        + 3 * t * (1 - t) * (1 - t) * controlPoints[1].getX()
                        + 3 * t * t * (1 - t) * controlPoints[2].getX()
                        + t * t * t * controlPoints[3].getX();
                double tmpY = (1 - t) * (1 - t) * (1 - t) * controlPoints[0].getY()
                        + 3 * t * (1 - t) * (1 - t) * controlPoints[1].getY()
                        + 3 * t * t * (1 - t) * controlPoints[2].getY()
                        + t * t * t * controlPoints[3].getY();
                res[i] = new Point2D.Double(tmpX, tmpY);
            }
            return res;
        }

        /**
         * Get sampled points of this cubic Bezier curve.
         *
         * @return sampled points
         */
        Point2D[] getCubicBezierCurve()
        {
            return curve;
        }

        @Override
        public String toString()
        {
            StringBuilder sb = new StringBuilder();
            for (Point2D p : controlPoints)
            {
                if (sb.length() > 0)
                {
                    sb.append(' ');
                }
                sb.append(p);
            }
            return "Cubic Bezier curve{control points p0, p1, p2, p3: " + sb + "}";
        }
    }