commons-geometry-euclidean/src/test/java/org/apache/commons/geometry/euclidean/internal/EuclideanUtilsTest.java

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 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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
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 * 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
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package org.apache.commons.geometry.euclidean.internal;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.function.Function;

import org.apache.commons.geometry.core.GeometryTestUtils;
import org.apache.commons.geometry.core.precision.DoublePrecisionContext;
import org.apache.commons.geometry.core.precision.EpsilonDoublePrecisionContext;
import org.apache.commons.geometry.euclidean.EuclideanTestUtils;
import org.apache.commons.geometry.euclidean.threed.Vector3D;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

public class EuclideanUtilsTest {

    private static final double TEST_EPS = 1e-10;

    private static final DoublePrecisionContext TEST_PRECISION =
            new EpsilonDoublePrecisionContext(TEST_EPS);

    @Test
    public void testConvexPolygonToTriangleFan_threeVertices() {
        // arrange
        final Vector3D p1 = Vector3D.ZERO;
        final Vector3D p2 = Vector3D.of(1, 0, 0);
        final Vector3D p3 = Vector3D.of(0, 1, 0);

        final List<List<Vector3D>> tris = new ArrayList<>();

        // act
        EuclideanUtils.convexPolygonToTriangleFan(Arrays.asList(p1, p2, p3), tris::add);

        // assert
        Assertions.assertEquals(1, tris.size());
        EuclideanTestUtils.assertVertexLoopSequence(Arrays.asList(p1, p2, p3), tris.get(0), TEST_PRECISION);
    }

    @Test
    public void testConvexPolygonToTriangleFan_fourVertices() {
        // arrange
        final Vector3D p1 = Vector3D.ZERO;
        final Vector3D p2 = Vector3D.of(1, 0, 0);
        final Vector3D p3 = Vector3D.of(1, 1, 0);
        final Vector3D p4 = Vector3D.of(0, 1, 0);

        final List<List<Vector3D>> tris = new ArrayList<>();

        // act
        EuclideanUtils.convexPolygonToTriangleFan(Arrays.asList(p1, p2, p3, p4), tris::add);

        // assert
        Assertions.assertEquals(2, tris.size());

        EuclideanTestUtils.assertVertexLoopSequence(Arrays.asList(p1, p2, p3), tris.get(0), TEST_PRECISION);
        EuclideanTestUtils.assertVertexLoopSequence(Arrays.asList(p1, p3, p4), tris.get(1), TEST_PRECISION);
    }

    @Test
    public void testConvexPolygonToTriangleFan_fourVertices_chooseLargestInteriorAngleForBase() {
        // arrange
        final Vector3D p1 = Vector3D.ZERO;
        final Vector3D p2 = Vector3D.of(1, 0, 0);
        final Vector3D p3 = Vector3D.of(2, 1, 0);
        final Vector3D p4 = Vector3D.of(1.5, 1, 0);

        final List<List<Vector3D>> tris = new ArrayList<>();

        // act
        EuclideanUtils.convexPolygonToTriangleFan(Arrays.asList(p1, p2, p3, p4), tris::add);

        // assert
        Assertions.assertEquals(2, tris.size());
        EuclideanTestUtils.assertVertexLoopSequence(Arrays.asList(p4, p1, p2), tris.get(0), TEST_PRECISION);
        EuclideanTestUtils.assertVertexLoopSequence(Arrays.asList(p4, p2, p3), tris.get(1), TEST_PRECISION);
    }

    @Test
    public void testConvexPolygonToTriangleFan_fourVertices_distancesLessThanPrecision() {
        // This test checks that the triangle fan algorithm is not affected by the distances between
        // the vertices, just as long as the points are not exactly equal. Callers are responsible for
        // ensuring that the points are actually distinct according to the relevant precision context.

        // arrange
        final Vector3D p1 = Vector3D.ZERO;
        final Vector3D p2 = Vector3D.of(1e-20, 0, 0);
        final Vector3D p3 = Vector3D.of(1e-20, 1e-20, 0);
        final Vector3D p4 = Vector3D.of(0, 1e-20, 0);

        final List<List<Vector3D>> tris = new ArrayList<>();

        // act
        EuclideanUtils.convexPolygonToTriangleFan(Arrays.asList(p1, p2, p3, p4), tris::add);

        // assert
        Assertions.assertEquals(2, tris.size());
        EuclideanTestUtils.assertVertexLoopSequence(Arrays.asList(p1, p2, p3), tris.get(0), TEST_PRECISION);
        EuclideanTestUtils.assertVertexLoopSequence(Arrays.asList(p1, p3, p4), tris.get(1), TEST_PRECISION);
    }

    @Test
    public void testConvexPolygonToTriangleFan_sixVertices() {
        // arrange
        final Vector3D p1 = Vector3D.ZERO;
        final Vector3D p2 = Vector3D.of(1, -1, 0);
        final Vector3D p3 = Vector3D.of(1.5, -1, 0);
        final Vector3D p4 = Vector3D.of(5, 0, 0);
        final Vector3D p5 = Vector3D.of(3, 1, 0);
        final Vector3D p6 = Vector3D.of(0.5, 1, 0);

        final List<List<Vector3D>> tris = new ArrayList<>();

        // act
        EuclideanUtils.convexPolygonToTriangleFan(Arrays.asList(p1, p2, p3, p4, p5, p6), tris::add);

        // assert
        Assertions.assertEquals(4, tris.size());
        EuclideanTestUtils.assertVertexLoopSequence(Arrays.asList(p3, p4, p5), tris.get(0), TEST_PRECISION);
        EuclideanTestUtils.assertVertexLoopSequence(Arrays.asList(p3, p5, p6), tris.get(1), TEST_PRECISION);
        EuclideanTestUtils.assertVertexLoopSequence(Arrays.asList(p3, p6, p1), tris.get(2), TEST_PRECISION);
        EuclideanTestUtils.assertVertexLoopSequence(Arrays.asList(p3, p1, p2), tris.get(3), TEST_PRECISION);
    }

    @Test
    public void testConvexPolygonToTriangleFan_notEnoughVertices() {
        // arrange
        final String baseMsg = "Cannot create triangle fan: 3 or more vertices are required but found only ";

        // act/assert
        GeometryTestUtils.assertThrowsWithMessage(() -> {
            EuclideanUtils.convexPolygonToTriangleFan(Collections.emptyList(), Function.identity());
        }, IllegalArgumentException.class, baseMsg + "0");

        GeometryTestUtils.assertThrowsWithMessage(() -> {
            EuclideanUtils.convexPolygonToTriangleFan(Collections.singletonList(Vector3D.ZERO), Function.identity());
        }, IllegalArgumentException.class, baseMsg + "1");

        GeometryTestUtils.assertThrowsWithMessage(() -> {
            EuclideanUtils.convexPolygonToTriangleFan(Arrays.asList(Vector3D.ZERO, Vector3D.of(1, 0, 0)), Function.identity());
        }, IllegalArgumentException.class, baseMsg + "2");
    }
}