Unity动态构建Mesh来绘制任意多边形（雷达图效果）

由于很多同学未能实现该功能，特此补传一个Demo工程（版本Unity2019.1.8f1），可通过以下链接下载：https://download.csdn.net/download/linxinfa/11956009

使用场景

雷达图

原理

动态创建一个Mesh对象，设置其三角形和顶点数据，然后将该Mesh赋值给MeshFilter组件，最后通过MeshRenderer组件将其绘制出来。

步骤

1. 复制脚本：将文章下方的脚本复制到工程中。
2. 创建空物体：在场景中创建一个空物体，将其命名为Mesh，并为其挂载PolygonDrawer组件。
3. 创建Sphere物体：在Mesh物体下创建N个Sphere。
4. 创建材质球：创建一个材质球，选择所需的Shader，例如本文使用的是Unlit/Color，并将颜色调整为蓝色。
5. 赋值材质球：将创建好的材质球赋值给PolygonDrawer组件。
6. 赋值Sphere物体：将N个Sphere赋值给PolygonDrawer组件（请注意N个Sphere的摆放顺序，本文的脚本仅支持顺时针或逆时针顺序）。
7. 运行Unity：运行Unity项目，运行后即可看到动态构建的多边形Mesh效果。

补充说明

评论区有同学反馈存在问题，我分别使用Unity5.x、Unity2017和Unity2019进行了测试，均能正常显示。

效果展示

运行项目后，将呈现出动态构建的多边形Mesh效果，类似雷达图。

代码实现

MethodExtensionForUnity.cs

using UnityEngine;

// Unity的一些扩展方法
static public class MethodExtensionForUnity
{
/// <summary>
/// 获取或添加一个组件。使用示例：
/// BoxCollider boxCollider = transform.GetOrAddComponent<BoxCollider>();
/// </summary>
static public T GetOrAddComponent<T>(this Component child, bool set_enable = false) where T : Component
{
T result = child.GetComponent<T>();
if (result == null)
{
result = child.gameObject.AddComponent<T>();
}
var bcomp = result as Behaviour;
if (set_enable)
{
if (bcomp != null) bcomp.enabled = true;
}
return result;
}

static public T GetOrAddComponent<T>(this GameObject go) where T : Component
{
T result = go.transform.GetComponent<T>();
if (result == null)
{
result = go.AddComponent<T>();
}
var bcomp = result as Behaviour;
if (bcomp != null) bcomp.enabled = true;
return result;
}

public static void walk(this GameObject o, System.Action<GameObject> f)
{
f(o);

int numChildren = o.transform.childCount;

for (int i = 0; i < numChildren; ++i)
{
walk(o.transform.GetChild(i).gameObject, f);
}
}
}

Triangulator.cs

using UnityEngine;
using System.Collections.Generic;

public class Triangulator
{
private List<Vector2> m_points = new List<Vector2>();

public Triangulator(Vector2[] points)
{
m_points = new List<Vector2>(points);
}

public int[] Triangulate()
{
List<int> indices = new List<int>();

int n = m_points.Count;
if (n < 3)
return indices.ToArray();

int[] V = new int[n];
if (Area() > 0)
{
for (int v = 0; v < n; v++)
V[v] = v;
}
else
{
for (int v = 0; v < n; v++)
V[v] = (n - 1) - v;
}

int nv = n;
int count = 2 * nv;
for (int m = 0, v = nv - 1; nv > 2; )
{
if ((count--) <= 0)
return indices.ToArray();

int u = v;
if (nv <= u)
u = 0;
v = u + 1;
if (nv <= v)
v = 0;
int w = v + 1;
if (nv <= w)
w = 0;

if (Snip(u, v, w, nv, V))
{
int a, b, c, s, t;
a = V[u];
b = V[v];
c = V[w];
indices.Add(a);
indices.Add(b);
indices.Add(c);
m++;
for (s = v, t = v + 1; t < nv; s++, t++)
V[s] = V[t];
nv--;
count = 2 * nv;
}
}

indices.Reverse();
return indices.ToArray();
}

private float Area()
{
int n = m_points.Count;
float A = 0.0f;
for (int p = n - 1, q = 0; q < n; p = q++)
{
Vector2 pval = m_points[p];
Vector2 qval = m_points[q];
A += pval.x * qval.y - qval.x * pval.y;
}
return (A * 0.5f);
}

private bool Snip(int u, int v, int w, int n, int[] V)
{
int p;
Vector2 A = m_points[V[u]];
Vector2 B = m_points[V[v]];
Vector2 C = m_points[V[w]];
if (Mathf.Epsilon > (((B.x - A.x) * (C.y - A.y)) - ((B.y - A.y) * (C.x - A.x))))
return false;
for (p = 0; p < n; p++)
{
if ((p == u) || (p == v) || (p == w))
continue;
Vector2 P = m_points[V[p]];
if (InsideTriangle(A, B, C, P))
return false;
}
return true;
}

private bool InsideTriangle(Vector2 A, Vector2 B, Vector2 C, Vector2 P)
{
float ax, ay, bx, by, cx, cy, apx, apy, bpx, bpy, cpx, cpy;
float cCROSSap, bCROSScp, aCROSSbp;

ax = C.x - B.x; ay = C.y - B.y;
bx = A.x - C.x; by = A.y - C.y;
cx = B.x - A.x; cy = B.y - A.y;
apx = P.x - A.x; apy = P.y - A.y;
bpx = P.x - B.x; bpy = P.y - B.y;
cpx = P.x - C.x; cpy = P.y - C.y;

aCROSSbp = ax * bpy - ay * bpx;
cCROSSap = cx * apy - cy * apx;
bCROSScp = bx * cpy - by * cpx;

return ((aCROSSbp >= 0.0f) && (bCROSScp >= 0.0f) && (cCROSSap >= 0.0f));
}
}

PolygonDrawer.cs

using UnityEngine;

/// <summary>
/// 绘制多边形
/// TODO: 存在两点重合时绘制有问题
/// </summary>
public class PolygonDrawer : MonoBehaviour
{
public Material material;
public Transform[] vertices;
private MeshRenderer mRenderer;
private MeshFilter mFilter;

void Start()
{
Draw();
}

void Update()
{
Draw();
}

[ContextMenu("Draw")]
public void Draw()
{
Vector2[] vertices2D = new Vector2[vertices.Length];
Vector3[] vertices3D = new Vector3[vertices.Length];
for (int i = 0; i < vertices.Length; i++)
{
Vector3 vertice = vertices[i].localPosition;
vertices2D[i] = new Vector2(vertice.x, vertice.y);
vertices3D[i] = vertice;
}

Triangulator tr = new Triangulator(vertices2D);
int[] triangles = tr.Triangulate();

Mesh mesh = new Mesh();
mesh.vertices = vertices3D;
mesh.triangles = triangles;

if (mRenderer == null)
{
mRenderer = gameObject.GetOrAddComponent<MeshRenderer>();
}
mRenderer.material = material;
if (mFilter == null)
{
mFilter = gameObject.GetOrAddComponent<MeshFilter>();
}
mFilter.mesh = mesh;
}
}