Unityにて、2DオブジェクトをLine Rendererで引いた線で分割できるようにしたいです。

実現したいこと

2Dオブジェクト(折り紙)をハサミで切るアクションを実現させたいです。

発生している問題・分からないこと

線を引いた所だけを消去して、残った部分はそれぞれにPolygonCollider2Dをつけて折り紙の断片オブジェクトとしてゲーム内に残したいです。

該当のソースコード

C#
1// タッチで線を引いてその線上の点を取得するコードです。RayCastは切断対象の折り紙を取得し、CreateCutPieceで折り紙を切断して断片を作ります。
2
3using UnityEngine;
4using System.Collections.Generic;
5using Clipper2Lib;
6
7public class ScissorsTool : MonoBehaviour
8{
9    private LineRenderer lineRenderer;
10    private List<Vector3> points = new List<Vector3>();
11    private bool isDrawing = false;
12    private bool wasScissorsMode = false;
13
14    void Start()
15    {
16        lineRenderer = GetComponent<LineRenderer>();
17        lineRenderer.positionCount = 0;
18        lineRenderer.widthMultiplier = 0.2f;
19    }
20
21    void Update()
22    {
23        bool isScissorsMode = GameModeManager.Instance.IsScissorsMode;
24
25        if (wasScissorsMode && !isScissorsMode) {
26            isDrawing = false;
27            lineRenderer.positionCount = 0;
28            points.Clear();
29        }
30
31        wasScissorsMode = isScissorsMode;
32
33        if (!isScissorsMode)
34            return;
35
36        // マウスでハサミを追従（またはタッチ）
37        if (Input.GetMouseButtonDown(0))
38        {
39            StartDrawing();
40        }
41        else if (Input.GetMouseButton(0) && isDrawing)
42        {
43            Vector3 mousePos = Camera.main.ScreenToWorldPoint(Input.mousePosition);
44            mousePos.z = 0f;
45
46            if (points.Count == 0 || Vector3.Distance(points[points.Count - 1], mousePos) > 0.05f)
47            {
48                points.Add(mousePos);
49                lineRenderer.positionCount = points.Count;
50                lineRenderer.SetPosition(points.Count - 1, mousePos);
51            }
52        }
53        else if (Input.GetMouseButtonUp(0) && isDrawing)
54        {
55            EndDrawing();
56        }
57    }
58
59    void StartDrawing()
60    {
61        isDrawing = true;
62        points.Clear();
63        lineRenderer.positionCount = 0;
64    }
65
66    void EndDrawing()
67    {
68        isDrawing = false;
69
70        HashSet<GameObject> detectedOrigami = new HashSet<GameObject>();
71
72        for (int i = 0; i < points.Count - 1; i++)
73        {
74            Vector2 start = points[i];
75            Vector2 end = points[i + 1];
76            Vector2 dir = (end - start).normalized;
77            float distance = Vector2.Distance(start, end);
78
79            RaycastHit2D[] hits = Physics2D.RaycastAll(start, dir, distance, LayerMask.GetMask("Origami"));
80            foreach (var hit in hits)
81            {
82                detectedOrigami.Add(hit.collider.gameObject);
83            }
84        }
85
86        foreach (GameObject obj in detectedOrigami)
87        {
88            Debug.Log("検知: " + obj.name);
89        }
90        
91        OrigamiProcessor.CreateCutPiece(points, detectedOrigami);
92
93        foreach(var origami in detectedOrigami) {
94            Destroy(origami);
95        }
96    }
97}

C#
1// 折り紙を切って折り紙の断片を生成します。Clipper2Libというライブラリで実行しています。
2ここが一番の問題だと思われます。ハサミの切り取り線と切断対象の折り紙の形状を取得して、その形状の差分で断片(CutPart)を取得します。
3
4using UnityEngine;
5using System.Collections.Generic;
6using Clipper2Lib;
7
8public static class OrigamiProcessor
9{
10    const double scale = 10000;
11
12    public static Paths64 ConvertColliderToClipperPaths(PolygonCollider2D collider)
13    {
14        Paths64 paths = new Paths64();
15
16        for (int i = 0; i < collider.pathCount; i++)
17        {
18            Vector2[] points = collider.GetPath(i);
19            Path64 path = new Path64();
20
21            foreach (Vector2 point in points)
22            {
23                long x = (long)(point.x * scale);
24                long y = (long)(point.y * scale);
25                path.Add(new Point64(x, y));
26            }
27
28            paths.Add(path);
29        }
30
31        return paths;
32    }
33
34    public static Path64 ConvertCutLineToClipperPath(List<Vector2> localCutPoints)
35    {
36        Path64 cutPath = new Path64();
37
38        foreach (var point in localCutPoints)
39        {
40            long x = (long)(point.x * scale);
41            long y = (long)(point.y * scale);
42            cutPath.Add(new Point64(x, y));
43        }
44
45        return cutPath;
46    }
47
48    public static void CreateCutPiece(List<Vector3> points, HashSet<GameObject> detectedOrigami)
49    {
50        foreach(GameObject origami in detectedOrigami)
51        {
52            List<Vector2> localCutPoints = new List<Vector2>();
53
54            PolygonCollider2D polygon = origami.GetComponent<PolygonCollider2D>();
55            foreach (var point in points) {
56                localCutPoints.Add(polygon.transform.InverseTransformPoint(point));
57            }
58            
59            Paths64 subj = ConvertColliderToClipperPaths(polygon);
60            Path64 clip = ConvertCutLineToClipperPath(localCutPoints);
61
62            Paths64 cutResult = Clipper.Difference(subj, new Paths64 { clip }, FillRule.NonZero);
63
64            foreach (var poly in cutResult) {
65                // 新しい GameObject を作成
66                GameObject part = new GameObject("CutPart");
67                part.transform.position = origami.transform.position;
68                part.transform.rotation = origami.transform.rotation;
69                part.transform.localScale = origami.transform.localScale;
70
71                part.layer = origami.layer;
72
73                // PolygonCollider2Dを追加
74                var collider = part.AddComponent<PolygonCollider2D>();
75
76                // ワールド→ローカルに戻して設定
77                Vector2[] localPoints = new Vector2[poly.Count];
78                for (int i = 0; i < poly.Count; i++)
79                {
80                    localPoints[i] = new Vector2(
81                        (float)(poly[i].X / scale),
82                        (float)(poly[i].Y / scale)
83                    );
84                }
85
86                collider.SetPath(0, localPoints);
87
88                var originalPTM = origami.GetComponent<PolygonToMesh>();
89                var partPTM = part.AddComponent<PolygonToMesh>();
90                partPTM.origamiMaterial = originalPTM.origamiMaterial;
91            }
92        }
93    }
94}