概述
3d模型的任意切割一直是游戲開發里的一個很大的問題，模型切割的關鍵點就只有生成橫切面的新頂點以及切口紋理的縫合，理論上解決了這兩點，就近乎可以做到以假亂真的程度了。本篇文章就這兩點進行描述
詳細
一、准備工作
解壓縮后得到ClipDemo.unitypackage文件，將此文件導入unity5.45中，雙擊main場景，運行即可。運行后可以看到一個球體，對着球體拖動鼠標做切割動作，可以看到Hierarchy面板生成多個new Model，即為切割生成的模型，可以在Scene中拖動這些物體，可以看到是切割后的物體。壓縮包內容如下：
二、程序實現
如上圖所示，當切割模型時，對於切面上的三角面，無非是如圖中3種情況（正好切在三角形的某個頂點上幾乎不可能，不過也可以考慮在內，這里就不畫出來了），所以每個三角形正好被切到的時候，其自身內部應該生成新的頂點（圖中-1，-2點）。生成處新的頂點之后，我們需要將原來的一個三角形重新分割為如圖綠色的數字標志的三個三角形，也就是原來一個三角形被分為三個三角形。代碼如下：
MeshFilter mf = this.gameObject.GetComponent<MeshFilter>();
//頂點數組轉頂點容器
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]);
}
//三角形數組轉三角形容器
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坐標數組轉uv坐標容器
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]);
}
//頂點顏色數組轉頂點顏色容器
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]);
}
//檢查每個三角面，是否存在兩個頂點連接正好在直線上
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相連線段被切割
if ((point0.y - planeY)* (point1.y - planeY) < 0 && (point1.y - planeY) * (point2.y - planeY) < 0)
{
//截斷0-1之間的頂點
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));
//截斷1-2之間的頂點
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;
//插入頂點索引，以此構建新三角形
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相連線段被切割
else if ((point1.y - planeY) * (point2.y - planeY) < 0 && (point2.y - planeY) * (point0.y - planeY) < 0)
{
//截斷1-2之間的頂點
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));
//截斷0-2之間的頂點
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;
//插入頂點索引，以此構建新三角形
//{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相連線段被切割
else if((point0.y - planeY) * (point1.y - planeY) < 0 && (point2.y - planeY) * (point0.y - planeY) < 0)
{
//截斷0-1之間的頂點
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));
//截斷0-2之間的頂點
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;
//插入頂點索引，以此構建新三角形
//{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;
}
//篩選出切割面兩側的頂點索引
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);
}
}
//縫合切口
//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;
切出來的模型新生成的頂點是無序的，但是我們可以連接任意兩個無序頂點定為參考向量，然后其他任意頂點與參考向量中的起點連接形成新的向量，求得這兩個向量之間的夾角，利用這個夾角大小來排序，如圖所示：
頂點的排序算法如下：
//重新排序新生成的頂點,按照角度
List<SortAngle> SortAngleList = new List<SortAngle>();
for (int verticeIndex = verticeCount + 1; verticeIndex < verticeList.Count; verticeIndex++)
{
//計算角度,以0-1為參照
Vector3 vec1to0 = verticeList[verticeCount + 1] - verticeList[verticeCount];
Vector3 indexTo0 = verticeList[verticeIndex] - verticeList[verticeCount];
float moIndexto0 = indexTo0.magnitude;
float mo1to0 = vec1to0.magnitude;
float dotRes = Vector3.Dot(indexTo0, vec1to0);
if (moIndexto0 == 0.0f)
{
continue;
}
float angle = Mathf.Acos(dotRes / (mo1to0 * moIndexto0)); //Vector3.Angle(indexTo0.normalized, vec1to0.normalized);
bool isExis = false;
for (int i = 0; i < SortAngleList.Count; ++i)
{
//同樣角度，距離近的被剔除
if (Mathf.Abs(SortAngleList[i].Angle * 180.0f / Mathf.PI - angle * 180.0f / Mathf.PI) < 0.1f)
{
float dis1 = Vector3.Distance(verticeList[SortAngleList[i].Index], verticeList[verticeCount]);
float dis2 = Vector3.Distance(verticeList[verticeIndex], verticeList[verticeCount]);
if (dis2 >= dis1)
{
SortAngleList[i].Index = verticeIndex;
}
isExis = true;
break;
}
}
if (!isExis)
{
//Debug.Log(angle);
SortAngle sortAngle = new SortAngle();
sortAngle.Index = verticeIndex;
sortAngle.Angle = angle;
SortAngleList.Add(sortAngle);
}
}
SortAngleList.Sort();
三、運行效果
四、項目截圖
注：本文著作權歸作者，由demo大師發表，拒絕轉載，轉載需要作者授權