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/* PolyEdge.java -- An edge in a polygon, used for polygon filling

   Copyright (C) 2006 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2, or (at your option)

any later version.

GNU Classpath 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

General Public License for more details.

You should have received a copy of the GNU General Public License

along with GNU Classpath; see the file COPYING.  If not, write to the

Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301 USA.

Linking this library statically or dynamically with other modules is

making a combined work based on this library.  Thus, the terms and

conditions of the GNU General Public License cover the whole

combination.

As a special exception, the copyright holders of this library give you

permission to link this library with independent modules to produce an

executable, regardless of the license terms of these independent

modules, and to copy and distribute the resulting executable under

terms of your choice, provided that you also meet, for each linked

independent module, the terms and conditions of the license of that

module.  An independent module is a module which is not derived from

or based on this library.  If you modify this library, you may extend

this exception to your version of the library, but you are not

obligated to do so.  If you do not wish to do so, delete this

exception statement from your version. */

package gnu.java.awt.java2d;

import gnu.java.math.Fixed;

/**

 * An edge in a polygon.

 *

 * @author Roman Kennke (kennke@aicas.com)

 */

final class PolyEdge

  implements Comparable

{

  /**

   * The start and end coordinates of the edge. y0 is always smaller or equal

   * than y1.

   *

   * These values are stored as fixed-point decimals.

   */

  public int x0, y0, x1, y1;

  /**

   * The slope of the edge. This is dx / dy.

   *

   * This is a fixed point decimal.

   */

  private int slope;

  /**

   * The intersection of this edge with the current scanline.

   *

   * This is a fixed point decimal.

   */

  int xIntersection;

  /**

   * Indicates whether this edge is from the clip or from the target shape.

   */

  boolean isClip;

  /**

   * Implements a linked list for the edge pool.

   */

  PolyEdge poolNext;

  /**

   * Implements a linked list for the scanline edge lists.

   */

  PolyEdge scanlineNext;

  /**

   * Create an uninitialized edge.

   */

  PolyEdge()

  {

    // Nothing to do here.

  }

  /**

   * Creates a new PolyEdge with the specified coordinates.

   *

   * @param x0 the starting point, x coordinate

   * @param y0 the starting point, y coordinate

   * @param x1 the end point, x coordinate

   * @param y1 the end point, y coordinate

   */

  PolyEdge(int n, int x0, int y0, int x1, int y1, boolean clip)

  {

    init(n, x0, y0, x1, y1, clip);

  }

  /**

   * (Re-) Initializes this edge.

   *

   * @param x0

   * @param y0

   * @param x1

   * @param y1

   */

  void init(int n, int x0, int y0, int x1, int y1, boolean clip)

  {

    isClip = clip;

    if (y0 < y1)

      {

        this.x0 = x0;

        this.y0 = y0;

        this.x1 = x1;

        this.y1 = y1;

      }

    else

      {

        this.x0 = x1;

        this.y0 = y1;

        this.x1 = x0;

        this.y1 = y0;

      }

    slope = Fixed.div(n, this.x1 - this.x0, this.y1 - this.y0);

  }

  /**

   * Sorts PolyEdges by the x coordinate from the minimum x value.

   */

  public int compareTo(Object o)

  {

    PolyEdge other = (PolyEdge) o;

    int comp = 0;

    if (x0 < other.x0)

      comp = -1;

    else if (x0 > other.x0)

      comp = 1;

    return comp;

  }

  /**

   * Intersects this edge with the scanline at height y. The result is

   * stored in {@link #xIntersection}.

   *

   * @param y the scanline

   */

  void intersect(int n, int y)

  {

    int dy = y - y0;

    int dx = Fixed.mul(n, slope, dy);

    xIntersection = x0 + dx;

  }

  public String toString()

  {

    return "Edge: " + x0 + ", " + y0 + ", " + x1 + ", " + y1 + ", slope: "

           + slope + ", xIntersection: " + xIntersection

           + ", isClip: " + isClip;

  }

}