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JFreeChart is a class library, written in Java, for generating charts. Utilising the Java2D API, it supports a wide range of chart types including bar charts, pie charts, line charts, XY-plots, time series plots, Sankey charts and more.
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/* ===========================================================
 * JFreeChart : a free chart library for the Java(tm) platform
 * ===========================================================
 *
 * (C) Copyright 2000-2011, by Object Refinery Limited and Contributors.
 *
 * Project Info:  http://www.jfree.org/jfreechart/index.html
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
 * USA.
 *
 * [Oracle and Java are registered trademarks of Oracle and/or its affiliates. 
 * Other names may be trademarks of their respective owners.]
 *
 * ------------------
 * LineUtilities.java
 * ------------------
 * (C) Copyright 2008, by Object Refinery Limited and Contributors.
 *
 * Original Author:  David Gilbert (for Object Refinery Limited);
 * Contributor(s):   -;
 *
 * Changes
 * -------
 * 05-Nov-2008 : Version 1 (DG);
 *
 */

package org.jfree.chart.util;

import java.awt.geom.Line2D;
import java.awt.geom.Rectangle2D;

/**
 * Some utility methods for {@link Line2D} objects.
 *
 * @since 1.0.12
 */
public class LineUtilities {

    /**
     * Clips the specified line to the given rectangle.
     *
     * @param line  the line (null not permitted).
     * @param rect  the clipping rectangle (null not permitted).
     *
     * @return true if the clipped line is visible, and
     *     false otherwise.
     */
    public static boolean clipLine(Line2D line, Rectangle2D rect) {

        double x1 = line.getX1();
        double y1 = line.getY1();
        double x2 = line.getX2();
        double y2 = line.getY2();

        double minX = rect.getMinX();
        double maxX = rect.getMaxX();
        double minY = rect.getMinY();
        double maxY = rect.getMaxY();

        int f1 = rect.outcode(x1, y1);
        int f2 = rect.outcode(x2, y2);

        while ((f1 | f2) != 0) {
            if ((f1 & f2) != 0) {
                return false;
            }
            double dx = (x2 - x1);
            double dy = (y2 - y1);
            // update (x1, y1), (x2, y2) and f1 and f2 using intersections
            // then recheck
            if (f1 != 0) {
                // first point is outside, so we update it against one of the
                // four sides then continue
                if ((f1 & Rectangle2D.OUT_LEFT) == Rectangle2D.OUT_LEFT
                        && dx != 0.0) {
                    y1 = y1 + (minX - x1) * dy / dx;
                    x1 = minX;
                }
                else if ((f1 & Rectangle2D.OUT_RIGHT) == Rectangle2D.OUT_RIGHT
                        && dx != 0.0) {
                    y1 = y1 + (maxX - x1) * dy / dx;
                    x1 = maxX;
                }
                else if ((f1 & Rectangle2D.OUT_BOTTOM) == Rectangle2D.OUT_BOTTOM
                        && dy != 0.0) {
                    x1 = x1 + (maxY - y1) * dx / dy;
                    y1 = maxY;
                }
                else if ((f1 & Rectangle2D.OUT_TOP) == Rectangle2D.OUT_TOP
                        && dy != 0.0) {
                    x1 = x1 + (minY - y1) * dx / dy;
                    y1 = minY;
                }
                f1 = rect.outcode(x1, y1);
            }
            else if (f2 != 0) {
                // second point is outside, so we update it against one of the
                // four sides then continue
                if ((f2 & Rectangle2D.OUT_LEFT) == Rectangle2D.OUT_LEFT
                        && dx != 0.0) {
                    y2 = y2 + (minX - x2) * dy / dx;
                    x2 = minX;
                }
                else if ((f2 & Rectangle2D.OUT_RIGHT) == Rectangle2D.OUT_RIGHT
                        && dx != 0.0) {
                    y2 = y2 + (maxX - x2) * dy / dx;
                    x2 = maxX;
                }
                else if ((f2 & Rectangle2D.OUT_BOTTOM) == Rectangle2D.OUT_BOTTOM
                        && dy != 0.0) {
                    x2 = x2 + (maxY - y2) * dx / dy;
                    y2 = maxY;
                }
                else if ((f2 & Rectangle2D.OUT_TOP) == Rectangle2D.OUT_TOP
                        && dy != 0.0) {
                    x2 = x2 + (minY - y2) * dx / dy;
                    y2 = minY;
                }
                f2 = rect.outcode(x2, y2);
            }
        }

        line.setLine(x1, y1, x2, y2);
        return true;  // the line is visible - if it wasn't, we'd have
                      // returned false from within the while loop above

    }
}