基本思想

????计算任意模型体积的基本思想是体素化。我们可以首先计算出物体的包围盒大小，然后在包围盒内均匀等间隔的取点，最后计算点落在物体内与采样总点数的比值，即可求出模型的体积。

实现方法

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using System;

public class Volume : MonoBehaviour
{
    private int sampleCount = 100;//每个方向选取100个点，包围盒内一共选取了100万个点
    private void Start()
    {
        float volume = CalculateVolume();
    }
    //检测点是否在模型内部
    bool IsInCollider(MeshCollider other, Vector3 center, Vector3 point)
    {
        Vector3 direction = center - point;
        RaycastHit[] hits = Physics.RaycastAll(point, direction);
        foreach (RaycastHit hit in hits)
        {
            if (hit.collider == other)
            {
                // we hit it so we were outside it
                return false;
            }
        }

        // no hits probably means we're inside it
        return true;
    }
    public float CalculateVolume()
    {
        GameObject object1 = GameObject.Find("object1");//更改为场景中要计算体积的物体的名称
        MeshCollider object1_mc = object1.GetComponent<MeshCollider>();
        Vector3 object1_center = object1_mc.bounds.center;
        Matrix4x4 localToWorld_object1 = object1.transform.localToWorldMatrix;
        Vector3[] vertices_object1 = object1.GetComponent<MeshFilter>().mesh.vertices;
        float[] x = new float[vertices_object1.Length];
        float[] y = new float[vertices_object1.Length];
        float[] z = new float[ vertices_object1.Length];
        //将局部坐标转换为世界坐标，并传递给数组
        for (int i = 0; i < vertices_object1.Length; i++)
        {
            Vector3 world_v = localToWorld_object1.MultiplyPoint3x4(vertices_object1[i]);
            x[i] = world_v.x;
            y[i] = world_v.y;
            z[i] = world_v.z;
        }
        //从小到大排序
        Array.Sort(x);
        Array.Sort(y);
        Array.Sort(z);
        //包围盒三边长度
        float x_length = x[x.Length - 1] - x[0];
        float y_length = y[y.Length - 1] - y[0];
        float z_length = z[z.Length - 1] - z[0];
        //选点步长
        float lerp_x = x_length / sampleCount;
        float lerp_y = y_length / sampleCount;
        float lerp_z = z_length / sampleCount;
        int pointInside = 0;
        for (int i = 0; i < sampleCount; i++)
        {
            for (int j = 0; j < sampleCount; j++)
            {
                for (int k = 0; k < sampleCount; k++)
                {
                    Vector3 sampleDot = new Vector3(x[0] + i * lerp_x, y[0] + j * lerp_y, z[0] + k * lerp_z);
                    if (IsInCollider(object1_mc, object1_center, sampleDot))
                    {
                        pointInside++;
                    }
                }
            }
        }
        //计算模型体积，单位为立方米
        float volume = (float)pointInside / (sampleCount * sampleCount * sampleCount) * (x_length * y_length * z_length);
        Debug.Log("Volume："+ volume);
        return volume;
    }
    private void Update()
    {

    }
}