关于3d模型任意切割的思路

3d模型的任意切割一直是游戏开发里的一个很大的问题，主要的问题是在切面的纹理上，然而如果是单纯的切面片则并不存在切面纹理的问题，关于切面纹理的解决方案在下一篇文章中探讨，总之本文权当研究吧。先看看我切出来的效果

下面先看看切出平整切痕的原理吧，本文需要图形学的基础扎实。

如上图所示，当切割模型时，对于切面上的三角面，无非是如图中3种情况（正好切在三角形的某个顶点上几乎不可能，不过也可以考虑在内，这里就不画出来了），所以每个三角形正好被切到的时候，其自身内部应该生成新的顶点（图中-1，-2点）。生成处新的顶点之后，我们需要将原来的一个三角形重新分割为如图绿色的数字标志的三个三角形，也就是原来一个三角形被分为三个三角形。

所以我在代码中做的，就是将正好被切割的三角形重新划分为三个三角形。代码如下

/* * @authors: liangjian * @desc:*/using UnityEngine;using System.Collections;using System.Collections.Generic;public class ClipMesh : MonoBehaviour {// Use this for initializationvoid Start () {        MeshFilter mf = this.gameObject.GetComponent<MeshFilter>();        //顶点数组转顶点容器        List<Vector3> verticeList = new List<Vector3>();        int verticeCount = mf.mesh.vertices.Length;        for (int verticeIndex = 0; verticeIndex < verticeCount; ++verticeIndex)        {            verticeList.Add(mf.mesh.vertices[verticeIndex]);        }        //三角形数组转三角形容器        List<int> triangleList = new List<int>();        int triangleCount = mf.mesh.triangles.Length;        for (int triangleIndex = 0; triangleIndex < triangleCount; ++triangleIndex)        {            triangleList.Add(mf.mesh.triangles[triangleIndex]);        }        //uv坐标数组转uv坐标容器        List<Vector2> uvList = new List<Vector2>();        int uvCount = mf.mesh.uv.Length;        for (int uvIndex = 0; uvIndex < uvCount; ++uvIndex)        {            uvList.Add(mf.mesh.uv[uvIndex]);        }        //顶点颜色数组转顶点颜色容器        List<Vector3> normalList = new List<Vector3>();        int normalCount = mf.mesh.normals.Length;        for (int normalIndex = 0; normalIndex < normalCount; ++normalIndex)        {            normalList.Add(mf.mesh.normals[normalIndex]);        }        //检查每个三角面，是否存在两个顶点连接正好在直线上        for (int triangleIndex = 0; triangleIndex < triangleList.Count;)        {            int trianglePoint0 = triangleList[triangleIndex];            int trianglePoint1 = triangleList[triangleIndex + 1];            int trianglePoint2 = triangleList[triangleIndex + 2];                        Vector3 point0 = verticeList[trianglePoint0];            Vector3 point1 = verticeList[trianglePoint1];            Vector3 point2 = verticeList[trianglePoint2];            float planeY = 0.3f;            //0-1，1-2相连线段被切割            if ((point0.y - planeY)* (point1.y - planeY) < 0 && (point1.y - planeY) * (point2.y - planeY) < 0)            {                //截断0-1之间的顶点                float k01 = (point1.y - point0.y) / (planeY - point0.y);                float newPointX01 = (point1.x - point0.x) / k01 + point0.x;                float newPointZ01 = (point1.z - point0.z) / k01 + point0.z;                Vector3 newPoint0_1 = new Vector3(newPointX01, planeY, newPointZ01);                verticeList.Add(newPoint0_1);                //uv                if(uvList.Count > 0)                {                    Vector2 uv0 = uvList[trianglePoint0];                    Vector2 uv1 = uvList[trianglePoint1];                    float newUV_x = (uv1.x - uv0.x) / k01 + uv0.x;                    float newUV_y = (uv1.y - uv0.y) / k01 + uv0.y;                    uvList.Add(new Vector2(newUV_x, newUV_y));                }                //法向量                Vector3 normalX0 = normalList[trianglePoint0];                Vector3 normalX1 = normalList[trianglePoint1];                Vector3 normalX2 = normalList[trianglePoint2];                float newNoramlX01 = (normalX1.x - normalX0.x) / k01 + normalX0.x;                float newNoramlY01 = (normalX1.y - normalX0.y) / k01 + normalX0.y;                float newNoramlZ01 = (normalX1.z - normalX0.z) / k01 + normalX0.z;                normalList.Add(new Vector3(newNoramlX01, newNoramlY01, newNoramlZ01));                //截断1-2之间的顶点                float k12 = (point2.y - point1.y) / (planeY - point1.y);                float newPointX12 = (point2.x - point1.x) / k12 + point1.x;                float newPointZ12 = (point2.z - point1.z) / k12 + point1.z;                Vector3 newPoint1_2 = new Vector3(newPointX12, planeY, newPointZ12);                verticeList.Add(newPoint1_2);                if (uvList.Count > 0)                {                    Vector2 uv1 = uvList[trianglePoint1];                    Vector2 uv2 = uvList[trianglePoint2];                    float newUV_x = (uv2.x - uv1.x) / k12 + uv1.x;                    float newUV_y = (uv2.y - uv1.y) / k12 + uv1.y;                    uvList.Add(new Vector2(newUV_x, newUV_y));                }                //法向量                float newNoramlX12 = (normalX2.x - normalX1.x) / k12 + normalX1.x;                float newNoramlY12 = (normalX2.y - normalX1.y) / k12 + normalX1.y;                float newNoramlZ12 = (normalX2.z - normalX1.z) / k12 + normalX1.z;                normalList.Add(new Vector3(newNoramlX12, newNoramlY12, newNoramlZ12));                int newVerticeCount = verticeList.Count;                //插入顶点索引，以此构建新三角形                triangleList.Insert(triangleIndex + 1, newVerticeCount - 2);                triangleList.Insert(triangleIndex + 2, newVerticeCount - 1);                triangleList.Insert(triangleIndex + 3, newVerticeCount - 1);                triangleList.Insert(triangleIndex + 4, newVerticeCount - 2);                triangleList.Insert(triangleIndex + 6, trianglePoint0);                triangleList.Insert(triangleIndex + 7, newVerticeCount - 1);            }            //1-2，2-0相连线段被切割            else if ((point1.y - planeY) * (point2.y - planeY) < 0 && (point2.y - planeY) * (point0.y - planeY) < 0)            {                //截断1-2之间的顶点                float k12 = (point2.y - point1.y) / (planeY - point1.y);                float newPointX12 = (point2.x - point1.x) / k12 + point1.x;                float newPointZ12 = (point2.z - point1.z) / k12 + point1.z;                Vector3 newPoint1_2 = new Vector3(newPointX12, planeY, newPointZ12);                verticeList.Add(newPoint1_2);                if (uvList.Count > 0)                {                    Vector2 uv1 = uvList[trianglePoint1];                    Vector2 uv2 = uvList[trianglePoint2];                    float newUV_x = (uv2.x - uv1.x) / k12 + uv1.x;                    float newUV_y = (uv2.y - uv1.y) / k12 + uv1.y;                    uvList.Add(new Vector2(newUV_x, newUV_y));                }                //法向量                Vector3 normalX0 = normalList[trianglePoint0];                Vector3 normalX1 = normalList[trianglePoint1];                Vector3 normalX2 = normalList[trianglePoint2];                float newNoramlX12 = (normalX2.x - normalX1.x) / k12 + normalX1.x;                float newNoramlY12 = (normalX2.y - normalX1.y) / k12 + normalX1.y;                float newNoramlZ12 = (normalX2.z - normalX1.z) / k12 + normalX1.z;                normalList.Add(new Vector3(newNoramlX12, newNoramlY12, newNoramlZ12));                //截断0-2之间的顶点                float k02 = (point2.y - point0.y) / (planeY - point0.y);                float newPointX02 = (point2.x - point0.x) / k02 + point0.x;                float newPointZ02 = (point2.z - point0.z) / k02 + point0.z;                Vector3 newPoint0_2 = new Vector3(newPointX02, planeY, newPointZ02);                verticeList.Add(newPoint0_2);                //uv                if (uvList.Count > 0)                {                    Vector2 uv0 = uvList[trianglePoint0];                    Vector2 uv2 = uvList[trianglePoint2];                    float newUV_x = (uv2.x - uv0.x) / k02 + uv0.x;                    float newUV_y = (uv2.y - uv0.y) / k02 + uv0.y;                    uvList.Add(new Vector2(newUV_x, newUV_y));                }                //法向量                float newNoramlX02 = (normalX1.x - normalX0.x) / k02 + normalX0.x;                float newNoramlY02 = (normalX1.y - normalX0.y) / k02 + normalX0.y;                float newNoramlZ02 = (normalX1.z - normalX0.z) / k02 + normalX0.z;                normalList.Add(new Vector3(newNoramlX02, newNoramlY02, newNoramlZ02));                                int newVerticeCount = verticeList.Count;                //插入顶点索引，以此构建新三角形                //{0}                //{1}                triangleList.Insert(triangleIndex + 2, newVerticeCount - 2);                triangleList.Insert(triangleIndex + 3, newVerticeCount - 1);                triangleList.Insert(triangleIndex + 4, newVerticeCount - 2);                //{2}                                triangleList.Insert(triangleIndex + 6, newVerticeCount - 1);                triangleList.Insert(triangleIndex + 7, trianglePoint0);                triangleList.Insert(triangleIndex + 8, newVerticeCount - 2);            }            //0-1，2-0相连线段被切割            else if((point0.y - planeY) * (point1.y - planeY) < 0 && (point2.y - planeY) * (point0.y - planeY) < 0)            {                //截断0-1之间的顶点                float k01 = (point1.y - point0.y) / (planeY - point0.y);                float newPointX01 = (point1.x - point0.x) / k01 + point0.x;                float newPointZ01 = (point1.z - point0.z) / k01 + point0.z;                Vector3 newPoint0_1 = new Vector3(newPointX01, planeY, newPointZ01);                verticeList.Add(newPoint0_1);                //uv                if (uvList.Count > 0)                {                    Vector2 uv0 = uvList[trianglePoint0];                    Vector2 uv1 = uvList[trianglePoint1];                    float newUV_x = (uv1.x - uv0.x) / k01 + uv0.x;                    float newUV_y = (uv1.y - uv0.y) / k01 + uv0.y;                    uvList.Add(new Vector2(newUV_x, newUV_y));                }                //法向量                Vector3 normalX0 = normalList[trianglePoint0];                Vector3 normalX1 = normalList[trianglePoint1];                Vector3 normalX2 = normalList[trianglePoint2];                float newNoramlX01 = (normalX1.x - normalX0.x) / k01 + normalX0.x;                float newNoramlY01 = (normalX1.y - normalX0.y) / k01 + normalX0.y;                float newNoramlZ01 = (normalX1.z - normalX0.z) / k01 + normalX0.z;                normalList.Add(new Vector3(newNoramlX01, newNoramlY01, newNoramlZ01));                //截断0-2之间的顶点                float k02 = (point2.y - point0.y) / (planeY - point0.y);                float newPointX02 = (point2.x - point0.x) / k02 + point0.x;                float newPointZ02 = (point2.z - point0.z) / k02 + point0.z;                Vector3 newPoint0_2 = new Vector3(newPointX02, planeY, newPointZ02);                verticeList.Add(newPoint0_2);                //uv                if (uvList.Count > 0)                {                    Vector2 uv0 = uvList[trianglePoint0];                    Vector2 uv2 = uvList[trianglePoint2];                    float newUV_x = (uv2.x - uv0.x) / k02 + uv0.x;                    float newUV_y = (uv2.y - uv0.y) / k02 + uv0.y;                    uvList.Add(new Vector2(newUV_x, newUV_y));                }                //法向量                float newNoramlX02 = (normalX1.x - normalX0.x) / k02 + normalX0.x;                float newNoramlY02 = (normalX1.y - normalX0.y) / k02 + normalX0.y;                float newNoramlZ02 = (normalX1.z - normalX0.z) / k02 + normalX0.z;                normalList.Add(new Vector3(newNoramlX02, newNoramlY02, newNoramlZ02));                                int newVerticeCount = verticeList.Count;                //插入顶点索引，以此构建新三角形                //{0}                triangleList.Insert(triangleIndex + 1, newVerticeCount - 2);                triangleList.Insert(triangleIndex + 2, newVerticeCount - 1);                triangleList.Insert(triangleIndex + 3, newVerticeCount - 2);                //{1}                //{2}                                triangleList.Insert(triangleIndex + 6, trianglePoint2);                triangleList.Insert(triangleIndex + 7, newVerticeCount - 1);                triangleList.Insert(triangleIndex + 8, newVerticeCount - 2);            }            //只有0-1被切            else if((point0.y - planeY) * (point1.y - planeY) < 0)            {                Debug.Log("只有01被切");            }            //只有1-2被切            else if ((point1.y - planeY) * (point2.y - planeY) < 0)            {                Debug.Log("只有12被切");            }            //只有2-0被切            else if ((point2.y - planeY) * (point0.y - planeY) < 0)            {                Debug.Log("只有02被切");            }            triangleIndex += 3;        }        //筛选出切割面两侧的顶点索引        List<int> triangles1 = new List<int>();        List<int> triangles2 = new List<int>();        for (int triangleIndex = 0; triangleIndex < triangleList.Count; triangleIndex += 3)        {            int trianglePoint0 = triangleList[triangleIndex];            int trianglePoint1 = triangleList[triangleIndex + 1];            int trianglePoint2 = triangleList[triangleIndex + 2];                        Vector3 point0 = verticeList[trianglePoint0];            Vector3 point1 = verticeList[trianglePoint1];            Vector3 point2 = verticeList[trianglePoint2];            //切割面            float planeY = 0.3f;            if(point0.y > planeY || point1.y > planeY || point2.y > planeY)            {                triangles1.Add(trianglePoint0);                triangles1.Add(trianglePoint1);                triangles1.Add(trianglePoint2);            }            else            {                triangles2.Add(trianglePoint0);                triangles2.Add(trianglePoint1);                triangles2.Add(trianglePoint2);            }        }        //缝合切口        //for (int verticeIndex = verticeCount; verticeIndex < verticeList.Count - 2; ++verticeIndex)        //{        //    triangles1.Add(verticeIndex + 2);        //    triangles1.Add(verticeIndex);        //    triangles1.Add(verticeCount);        //    triangles2.Add(verticeCount);        //    triangles2.Add(verticeIndex);        //    triangles2.Add(verticeIndex + 2);        //}        mf.mesh.vertices = verticeList.ToArray();        mf.mesh.triangles = triangles1.ToArray();        if (uvList.Count > 0)        {            mf.mesh.uv = uvList.ToArray();        }        mf.mesh.normals = normalList.ToArray();        //分割模型        GameObject newModel = new GameObject("New Model");        MeshFilter meshFilter = newModel.AddComponent<MeshFilter>();        meshFilter.mesh.vertices = mf.mesh.vertices;        meshFilter.mesh.triangles = triangles2.ToArray();        meshFilter.mesh.uv = mf.mesh.uv;        meshFilter.mesh.normals = mf.mesh.normals;        Renderer newRenderer = newModel.AddComponent<MeshRenderer>();        newRenderer.material = this.gameObject.GetComponent<MeshRenderer>().material;    }}