Computes the triangulation of a polygon with ear-clipping algorithm. - Java 2D Graphics

Java examples for 2D Graphics:Polygon

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Description

Computes the triangulation of a polygon with ear-clipping algorithm.

Demo Code

/*//from w  w w  .j av a 2  s.  c o  m
 *  Flingbox - An OpenSource physics sandbox for Google's Android
 *  Copyright (C) 2009  Jon Ander Pe?alba & Endika Guti?rrez
 *
 *  This program 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 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
 */
import java.util.ArrayList;

public class Main{
    /**
     * Computes the triangulation of a polygon with ear-clipping 
     * algorithm. 
     * @param Vector2Ds   Array of polygon's points
     * @return         Will return n-2 group of 3 points, for n sides polygon
     *                or null if not enough points
     */
    public static short[] triangulatePolygon(final Vector2D[] Vector2Ds) {
        final int Vector2DsCount = Vector2Ds.length;
        if (Vector2DsCount < 3)
            return null;

        // n-2 group of 3 Vector2Ds, for n sides polygon 
        short[] triangles = new short[3 * (Vector2DsCount - 2)];
        boolean[] included = new boolean[Vector2DsCount];

        int topVector2DIndex;
        float topVector2D;
        for (int trianglesCount = 0; trianglesCount < (Vector2DsCount - 3); ++trianglesCount) {
            topVector2DIndex = 0;
            topVector2D = Float.NEGATIVE_INFINITY;

            // Find top Vector2D to find triangle
            for (int i = 0; i < Vector2DsCount; i++) {
                // Find top Vector2D
                if (!included[i] && (Vector2Ds[i].i > topVector2D)) {
                    topVector2D = Vector2Ds[i].i;
                    topVector2DIndex = i;
                }
            }

            // Exclude Vector2D for next iteration
            included[topVector2DIndex] = true;

            // Save triangle
            int prevVector2D = topVector2DIndex; // Find previous Vector2D
            do {
                if (--prevVector2D < 0)
                    prevVector2D = Vector2DsCount - 1;
            } while (included[prevVector2D]);

            int nextVector2D = topVector2DIndex; // Find next Vector2D
            do {
                if (++nextVector2D >= Vector2DsCount)
                    nextVector2D = 0;
            } while (included[nextVector2D]);

            // Store triangle
            triangles[trianglesCount * 3] = (short) prevVector2D; // Store into array
            triangles[trianglesCount * 3 + 1] = (short) topVector2DIndex;
            triangles[trianglesCount * 3 + 2] = (short) nextVector2D;
        }

        return triangles;
    }
}

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