UnityのSceneビューでメッシュの法線を表示する

GizmosMeshNormalDrawer.cs

using UnityEngine;
using System.Linq;

public static class GizmosArrowDrawer
{
    public static void Draw(Vector3 pos, Vector3 direction, float arrowHeadLength = 0.25f, float arrowHeadAngle = 20.0f)
    {
        Gizmos.DrawRay(pos, direction);

        Vector3 right = Quaternion.LookRotation(direction) * Quaternion.Euler(0, 180 + arrowHeadAngle, 0) * new Vector3(0, 0, 1);
        Vector3 left = Quaternion.LookRotation(direction) * Quaternion.Euler(0, 180 - arrowHeadAngle, 0) * new Vector3(0, 0, 1);
        Gizmos.DrawRay(pos + direction, right * arrowHeadLength);
        Gizmos.DrawRay(pos + direction, left * arrowHeadLength);
    }

    public static void ForGizmo(Vector3 pos, Vector3 direction, Color color, float arrowHeadLength = 0.25f, float arrowHeadAngle = 20.0f)
    {
        Gizmos.color = color;
        Draw(pos, direction, arrowHeadLength, arrowHeadAngle);
    }
}

public class GizmosMeshNormalDrawer : MonoBehaviour
{
    [SerializeField]
    private Mesh mesh;

    [SerializeField, Range(0, 10000)]
    private int disableCount = 500;

    [SerializeField]
    private float arrowLength = 0.5f;

    void OnDrawGizmosSelected()
    {
        if (mesh == null)
        {
            return;
        }

        var vertexCount = mesh.vertices.Length;
        if (vertexCount > disableCount)
        {
            Debug.LogFormat("Disable normals because meshes has {0} vertices.", vertexCount);
            return;
        }

        for (int m = 0; m < mesh.subMeshCount; ++m)
        {
            for (int i = 0; i < mesh.vertices.Length; i += 1)
            {
                var pos = mesh.vertices[i];
                pos = Vector3.Scale(pos, transform.lossyScale);
                pos = transform.rotation * pos;
                pos += transform.position;
                var normal = mesh.normals[i];

                if (Vector3.zero != normal)
                {
                    GizmosArrowDrawer.ForGizmo(pos, normal.normalized * arrowLength, Color.cyan, arrowLength / 5);
                }
            }

            var triangles = mesh.GetTriangles(m);
            for (int i = 0; i < triangles.Length; i += 3)
            {
                var v1 = mesh.vertices[triangles[i]];
                var v2 = mesh.vertices[triangles[i+1]];
                var v3 = mesh.vertices[triangles[i+2]];
                var vec1 = v2 - v1;
                var vec2 = v3 - v1;

                var pos = (v1 + v2 + v3) / 3;
                pos = Vector3.Scale(pos, transform.lossyScale);
                pos = transform.rotation * pos;
                pos += transform.position;
                var normal = Vector3.Cross(vec1, vec2);

                if (Vector3.zero != normal)
                {
                    GizmosArrowDrawer.ForGizmo(pos, normal.normalized * arrowLength, Color.green, arrowLength / 5);
                }
            }
        }
    }
}