(轉)Unity3D點擊繪製二維模型線和三維模型線

下面是轉載別人的，缺點是隻能在xz平面上畫線，可以添加一個地板來測試，鼠標點擊地板進行畫線

當再次看這篇文章時，還是覺得非常喫力，因爲距離上一次轉載的時間有點長了，上次是看懂了，但沒有記錄下來，所以這次看時還是需要費點腦子纔再次看懂了，所以這次我在後面詳細的記錄了下來，最好自己能夠看懂原來作者的代碼，不能完全看懂也沒有關係，在最後我會解釋一下核心的代碼和核心的算法。 (2019年7月13日新增)

這兩天在研究畫線的東西。直到昨天才小有成效。拿出來和大家分享一下。先上圖：

以前曾經嘗試過用LineRender寫畫線的功能，但是在拐彎的時候會出現變形和扭曲。所以才決定用繪製Mesh的方法寫一個畫線的功能。

東西其實很簡單，稍微有一點數學的知識，用到了三角函數。還有一些關於構造Mesh的相關代碼。下面有草圖一張：

黑色的線框代表畫出來的模型線，PointA和PointB代表獲取的起始點和終結點，A,B,C,D爲Mesh的四個頂點。

已知起始點和終結點和線寬，就可以求出四個頂點的座標。並根據這四個頂點繪製出Mesh.

至於具體的實現細節，大家看代碼吧。

DrawMeshLine類：

using UnityEngine;  
using System.Collections;  
using System.Collections.Generic;  
  
public class DrawMeshLine : MonoBehaviour   
{  
    //線容器  
    List<Vector3> LinePointContainer;  
    //線寬  
    public float LineWidth = 0.5f;  
    //地形層  
    public int Layer = 8;  
    //線物體父物體  
    GameObject LineObj;  
      
    void Start ()   
    {  
        LinePointContainer = new List<Vector3>();  
        LineObj = new GameObject("Lines");  
    }  
      
    void Update ()   
    {  
        if(Input.GetMouseButtonDown(0))  
        {  
            Ray ray = Camera.mainCamera.ScreenPointToRay(Input.mousePosition);  
            RaycastHit hit;  
            if(Physics.Raycast(ray,out hit))  
            {  
                if(hit.transform.gameObject.layer != Layer)return;  
                LinePointContainer.Add(hit.point);  
            }  
            if(LinePointContainer.Count == 1)  
            {  
                //二維初始面片圓  
//              GameObject sphere = GameObject.CreatePrimitive(PrimitiveType.Sphere);  
//              sphere.transform.parent = LineObj.transform;  
//              sphere.transform.position = hit.point;  
//              sphere.transform.localScale = new Vector3(LineWidth * 2,0.01f,LineWidth * 2);  
//              sphere.renderer.material.shader = Shader.Find("GUI/Text Shader");  
//              sphere.renderer.material.SetColor("_Color",new Color(255,0,0,255) / 255);  
                  
                //三維初始球  
                GameObject sphere = GameObject.CreatePrimitive(PrimitiveType.Sphere);  
                sphere.transform.parent = LineObj.transform;  
                sphere.transform.position = new Vector3(hit.point.x,hit.point.y + LineWidth,hit.point.z);  
                sphere.transform.localScale = new Vector3(LineWidth * Mathf.Sqrt(8.0f),LineWidth * Mathf.Sqrt(8.0f),LineWidth * Mathf.Sqrt(8.0f));  
            }  
            if(LinePointContainer.Count > 1)  
            {  
                //畫二維面片線  
                //DrawLine2D(LinePointContainer[LinePointContainer.Count - 2],LinePointContainer[LinePointContainer.Count - 1]);  
                //畫三維立體線  
                DrawLine3D(LinePointContainer[LinePointContainer.Count - 2],LinePointContainer[LinePointContainer.Count - 1]);                   //第一個參數是起點，第二個參數是終點
            }  
        }  
        if(Input.GetMouseButtonDown(1))  
        {  
            //清空線容器  
            if(LinePointContainer.Count < 3)return;  
            DrawLine3D(LinePointContainer[LinePointContainer.Count - 1],LinePointContainer[0]);  
            LinePointContainer.Clear();  
        }  
        if(Input.GetKeyDown(KeyCode.Escape))  
        {  
            //清除所有線物體  
            LinePointContainer.Clear();  
            ClearLineObjects();  
        }  
    }  
      
    /// <summary>  
    /// 二維線  
    /// </summary>  
    /// <param name='PointA'>  
    /// 初始點  
    /// </param>  
    /// <param name='PointB'>  
    /// 結束點  
    /// </param>  
    void DrawLine2D(Vector3 PointA,Vector3 PointB)  
    {  
        float HorDisABx = PointB.x - PointA.x;  
        float HorDisABz = PointB.z - PointA.z;  
        float HorDisAB = Mathf.Sqrt(Mathf.Pow(HorDisABx,2) + Mathf.Pow(HorDisABz,2));  
          
        float offsetX = HorDisABz * LineWidth / HorDisAB;  
        float offsetZ = HorDisABx * LineWidth / HorDisAB;  
          
        Vector3 Point1 = new Vector3(PointA.x - offsetX,PointA.y,PointA.z + offsetZ);  
        Vector3 Point2 = new Vector3(PointA.x + offsetX,PointA.y,PointA.z - offsetZ);  
        Vector3 Point3 = new Vector3(PointB.x + offsetX,PointB.y,PointB.z - offsetZ);  
        Vector3 Point4 = new Vector3(PointB.x - offsetX,PointB.y,PointB.z + offsetZ);  
          
 
 
          
        GameObject go = new GameObject((LinePointContainer.Count - 1).ToString());  
        go.transform.parent = LineObj.transform;  
        Mesh mesh = go.AddComponent<MeshFilter>().mesh;  
        go.AddComponent<MeshRenderer>();  
        mesh.vertices = new Vector3[]{Point1,Point2,Point3,Point4};  
        mesh.triangles = new int[]{2,1,0,0,3,2};  
          
        GameObject sphere = GameObject.CreatePrimitive(PrimitiveType.Sphere);  
        sphere.transform.parent = LineObj.transform;  
        sphere.transform.position = PointB;  
        sphere.transform.localScale = new Vector3(LineWidth * 2,0.01f,LineWidth * 2);  
    }  
      
    /// <summary>  
    /// 三維線  
    /// </summary>  
    /// <param name='PointA'>  
    /// 初始點  
    /// </param>  
    /// <param name='PointB'>  
    /// 結束點  
    /// </param>  
    void DrawLine3D(Vector3 PointA,Vector3 PointB)  
    {  
        float HorDisABx = PointB.x - PointA.x;  
        float HorDisABz = PointB.z - PointA.z;  
        float HorDisAB = Mathf.Sqrt(Mathf.Pow(HorDisABx,2) + Mathf.Pow(HorDisABz,2));  //求起點和終點的模長
          
        float offsetX = HorDisABz * LineWidth / HorDisAB;  
        float offsetZ = HorDisABx * LineWidth / HorDisAB;  
          
        Vector3 Point1 = new Vector3(PointA.x - offsetX,PointA.y,PointA.z + offsetZ);  
        Vector3 Point2 = new Vector3(PointA.x + offsetX,PointA.y,PointA.z - offsetZ);  
        Vector3 Point3 = new Vector3(PointB.x + offsetX,PointB.y,PointB.z - offsetZ);  
        Vector3 Point4 = new Vector3(PointB.x - offsetX,PointB.y,PointB.z + offsetZ);  
          
        GameObject go1 = new GameObject((LinePointContainer.Count - 1).ToString() + "_1");  
        go1.transform.parent = LineObj.transform;  
        Mesh mesh1 = go1.AddComponent<MeshFilter>().mesh;  
        go1.AddComponent<MeshRenderer>();  
        mesh1.vertices = new Vector3[]{Point1,Point2,Point3,Point4};  
        mesh1.triangles = new int[]{2,1,0,0,3,2};  
          
        Vector3 Point5 = new Vector3(PointA.x - offsetX,PointA.y + 2 * LineWidth,PointA.z + offsetZ);  
        Vector3 Point6 = new Vector3(PointA.x + offsetX,PointA.y + 2 * LineWidth,PointA.z - offsetZ);  
        Vector3 Point7 = new Vector3(PointB.x + offsetX,PointB.y + 2 * LineWidth,PointB.z - offsetZ);  
        Vector3 Point8 = new Vector3(PointB.x - offsetX,PointB.y + 2 * LineWidth,PointB.z + offsetZ);  
          
        GameObject go2 = new GameObject((LinePointContainer.Count - 1).ToString() + "_2");  
        go2.transform.parent = LineObj.transform;  
        Mesh mesh2 = go2.AddComponent<MeshFilter>().mesh;  
        go2.AddComponent<MeshRenderer>();  
        mesh2.vertices = new Vector3[]{Point5,Point6,Point7,Point8};  
        mesh2.triangles = new int[]{2,1,0,0,3,2};  
          
        GameObject go3 = new GameObject((LinePointContainer.Count - 1).ToString() + "_3");  
        go3.transform.parent = LineObj.transform;  
        Mesh mesh3 = go3.AddComponent<MeshFilter>().mesh;  
        go3.AddComponent<MeshRenderer>();  
        mesh3.vertices = new Vector3[]{Point6,Point2,Point3,Point7};  
        mesh3.triangles = new int[]{2,1,0,0,3,2};  
          
        GameObject go4 = new GameObject((LinePointContainer.Count - 1).ToString() + "_4");  
        go4.transform.parent = LineObj.transform;  
        Mesh mesh4 = go4.AddComponent<MeshFilter>().mesh;  
        go4.AddComponent<MeshRenderer>();  
        mesh4.vertices = new Vector3[]{Point1,Point5,Point8,Point4};  
        mesh4.triangles = new int[]{2,1,0,0,3,2};  
          
        GameObject sphere = GameObject.CreatePrimitive(PrimitiveType.Sphere);  
        sphere.transform.parent = LineObj.transform;  
        sphere.transform.position = new Vector3(PointB.x,PointB.y + LineWidth,PointB.z);  
        sphere.transform.localScale = new Vector3(LineWidth * Mathf.Sqrt(8.0f),LineWidth * Mathf.Sqrt(8.0f),LineWidth * Mathf.Sqrt(8.0f));  
    }  
      
    void ClearLineObjects ()  
    {  
        for(int i = 0 ; i < LineObj.transform.childCount;i ++)  
        {  
            GameObject go = LineObj.transform.GetChild(i).gameObject;  
            Destroy(go);  
        }  
    }  
}

個人理解：

想象成一個幾何體，以ABCD爲地面，把地面擡高2 * LineWidth米作爲頂面EFGH

1 GameObject go1 = new GameObject((LinePointContainer.Count - 1).ToString() + "_1"); 這個是畫面ABCD

2 GameObject go2 = new GameObject((LinePointContainer.Count - 1).ToString() + "_2"); 這個是畫面EFGH

3 GameObject go3 = new GameObject((LinePointContainer.Count - 1).ToString() + "_3"); 這個是畫面BCGF

4 GameObject go4 = new GameObject((LinePointContainer.Count - 1).ToString() + "_4"); 這個是畫面ADHE

其中面ABFE和麪DCGH不用畫，畫了也沒有意義

(2019年7月13日新增)

其中PointA爲線的起點，PointB爲線的終點

上面的代碼：

Vector3 Point1 = new Vector3(PointA.x - offsetX,PointA.y,PointA.z + offsetZ);

Vector3 Point2 = new Vector3(PointA.x + offsetX,PointA.y,PointA.z - offsetZ);

Vector3 Point3 = new Vector3(PointB.x + offsetX,PointB.y,PointB.z - offsetZ);

Vector3 Point4 = new Vector3(PointB.x - offsetX,PointB.y,PointB.z + offsetZ);

Point1對應於上圖中的A點，Point2對應上圖的B點，Point3對應上圖中的C點，Point4對應上圖的D點

想要繪製出面 ABCD，在Unity3d中只能繪製出三角形，這時我們可以把面ABCD分成兩個三角面 : 面ABC和麪ADC

把點Point3、Point2、Point1兩兩相連，再渲染(至於如何把三角形渲染成面，不需要你管，Unity3D做了)，就成面ABC了

把點Point1、Point4、Point3兩兩相連，再渲染，就成面ADC了

當繪製出面ABC和麪ADC後，把這兩個面一組合，就形成了面ABCD,這時就有了下面的代碼：

mesh1.vertices = new Vector3[]{Point1,Point2,Point3,Point4};

mesh1.triangles = new int[]{2,1,0,0,3,2};

其中代碼 mesh1.triangles = new int[]{2,1,0,0,3,2}; 總共有6個數，連續三個數組成一組，這樣可以分成兩組 (2,1,0)和(0,3,2)

至於爲什麼是三個數爲一組，我猜你還缺乏Mesh基礎，請參考：https://blog.csdn.net/zxy13826134783/article/details/80114487

再看 mesh1.vertices[2]=Point3,mesh1.vertices[1]=Point2,mesh.vertices[0]=Point1, 數組下標一組合爲 (2,1,0), 把數組下標對應的點Point3、Point2、Point1 兩兩相連，不就成了三角形ABC了嗎，Unity3D自動把三角形ABC渲染成面ABC

同理mesh1.vertices[0]=Pont1,mesh1.vertices[3]=Point4,mesh1.vertices[2]=Point3,數組下標一組合爲 (0,3,2),把數組下標對應的點Point1、Point4、Point3 兩兩相連，不就成了三角形ADC了嗎，Unity3D自動把三角形ADC渲染成面ADC

把面ABC和麪ADC一組合就完成了面ABCD的繪製

同理，再把面EFGH、面BCGF、面ADHE繪製，最後把四個面一組合，就組成了空心的三維模型線(算是線吧)，如下圖：

(轉)Unity3D點擊繪製二維模型線和三維模型線

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