Triangulator2D.java

/*
 * Copyright (C) 2012 Alberto Irurueta Carro (alberto@irurueta.com)
 *
 * 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 com.irurueta.geometry;

import java.util.List;

/**
 * This class defines a triangulator for 2D polygons. Triangulators divide
 * polygons into triangles, which are the simplest geometric figure.
 * Criteria for triangulation depends on each triangulator implementation.
 */
public abstract class Triangulator2D {

    /**
     * Constant defining minimum vertices allowed in a polygon.
     */
    public static final int MIN_VERTICES = 3;

    /**
     * Constant defining default triangulator method.
     */
    public static final TriangulatorMethod DEFAULT_TRIANGULATOR_METHOD = TriangulatorMethod.VAN_GOGH_TRIANGULATOR;

    /**
     * Empty constructor.
     */
    protected Triangulator2D() {
    }

    /**
     * Returns triangulator method.
     * Each method implementation will divide polygons into triangles using
     * different techniques.
     *
     * @return Triangulator method.
     */
    public abstract TriangulatorMethod getMethod();

    /**
     * Triangulates provided polygon by dividing it into a set of triangles.
     *
     * @param polygon Polygon to be triangulated.
     * @return List of triangles forming the polygon that has been triangulated.
     * @throws TriangulatorException Raised if triangulation cannot be done.
     *                               Usually this indicates numerical instability or polygon degeneracy.
     */
    public abstract List<Triangle2D> triangulate(final Polygon2D polygon) throws TriangulatorException;

    /**
     * Triangulates a polygon formed by provided vertices.
     *
     * @param vertices List of points considered as vertices of a polygon.
     * @return List of triangles forming the polygon that has been triangulated.
     * @throws TriangulatorException Raised if triangulation cannot be done.
     *                               Usually this indicates numerical instability or polygon degeneracy.
     */
    public abstract List<Triangle2D> triangulate(final List<Point2D> vertices) throws TriangulatorException;

    /**
     * Triangulates a polygon formed by provided vertices.
     *
     * @param vertices List of points considered as vertices of a polygon.
     * @param indices  List where indices of original vertices will be stored.
     *                 This list can be used to refer to the original order of vertices. Notice
     *                 that vertices indices might be repeated because vertices might appear in
     *                 more than one triangle after triangulation. If this parameter is null,
     *                 indices won't be stored in this list.
     * @return List of triangles forming the polygon that has been triangulated.
     * @throws TriangulatorException Raised if triangulation cannot be done.
     *                               Usually this indicates numerical instability or polygon degeneracy.
     */
    public abstract List<Triangle2D> triangulate(final List<Point2D> vertices, final List<int[]> indices)
            throws TriangulatorException;

    /**
     * Instantiates a triangulator for 2D polygons using default method.
     *
     * @return A triangulator for 2D polygons.
     */
    public static Triangulator2D create() {
        return create(DEFAULT_TRIANGULATOR_METHOD);
    }

    /**
     * Instantiates a triangulator for 2D polygons using provided method.
     *
     * @param method A triangulator method.
     * @return A triangulator for 2D polygons.
     */
    public static Triangulator2D create(final TriangulatorMethod method) {
        //noinspection SwitchStatementWithTooFewBranches
        return switch (method) {
            default -> new VanGoghTriangulator2D();
        };
    }
}