[Unity]利用Mesh在Unity中繪製扇形圖片2

之前那篇文章後，和同事又就這個問題討論了一下，發現，其實不需要那麼死心眼畫n個三角形，因爲圖片本身除了圓以外的地方都是透明的， 畫出來也沒事。
這樣的話， 其實可以把正方形的圖片分成4個三角形，這樣的話，最多也就畫5個三角形就夠了。

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

[RequireComponent(typeof(MeshRenderer), typeof(MeshFilter))]
public class TestProgressBar : MonoBehaviour
{   
    public float radius = 2;
    [Range(0,360)]//把角度限制在0-360
    public float startAngleDegree = 0;
    [Range(0,360)]//把角度限制在0-360
    public float angleDegree = 100;
    public int angleDegreePrecision = 1000;
    public int radiusPrecision = 1000;
    //與之前的代碼相比, 已經不需要分割的三角形數了

    private MeshFilter meshFilter;

    private SectorMeshCreator creator = new SectorMeshCreator();

    [ExecuteInEditMode]
    private void Awake()
    {
        meshFilter = GetComponent<MeshFilter>();
    }

    private void Update()
    {
        meshFilter.mesh = creator.CreateMesh(radius, startAngleDegree, angleDegree, angleDegreePrecision, radiusPrecision);
    }

    //在Scene界面畫輔助線
    void OnDrawGizmos()
    {
        Gizmos.color = Color.gray;
        DrawMesh();
    }

    //在Scene界面畫輔助線
    void OnDrawGizmosSelected()
    {
        Gizmos.color = Color.green;
        DrawMesh();
    }

    private void DrawMesh()
    {
        Mesh mesh = creator.CreateMesh(radius, startAngleDegree, angleDegree, angleDegreePrecision, radiusPrecision);
        int[] tris = mesh.triangles;
        for (int i = 0; i < tris.Length; i += 3)
        {
            Gizmos.DrawLine(convert2World(mesh.vertices[tris[i]]), convert2World(mesh.vertices[tris[i + 1]]));
            Gizmos.DrawLine(convert2World(mesh.vertices[tris[i]]), convert2World(mesh.vertices[tris[i + 2]]));
            Gizmos.DrawLine(convert2World(mesh.vertices[tris[i + 1]]), convert2World(mesh.vertices[tris[i + 2]]));
        }
    }

    private Vector3 convert2World(Vector3 src)
    {
        return transform.TransformPoint(src);
    }

    private class SectorMeshCreator
    {
        private float radius;
        private float startAngleDegree;
        private float angleDegree;

        private Mesh cacheMesh;

        /// <summary>  
        /// 創建一個扇形Mesh  
        /// </summary>  
        /// <param name="radius">扇形半徑</param>  
        /// <param name="startAngleDegree">扇形開始角度</param> 
        /// <param name="angleDegree">扇形角度</param>  
        /// <param name="angleDegreePrecision">扇形角度精度（在滿足精度範圍內，認爲是同個角度）</param>  
        /// <param name="radiusPrecision">  
        /// <pre>  
        /// 扇形半價精度（在滿足半價精度範圍內，被認爲是同個半價）。  
        /// 比如：半價精度爲1000，則：1.001和1.002不被認爲是同個半徑。因爲放大1000倍之後不相等。  
        /// 如果半價精度設置爲100，則1.001和1.002可認爲是相等的。  
        /// </pre>  
        /// </param>  
        /// <returns></returns>  
        public Mesh CreateMesh(float radius, float startAngleDegree, float angleDegree, int angleDegreePrecision, int radiusPrecision)
        {
            if (checkDiff(radius, startAngleDegree, angleDegree, angleDegreePrecision, radiusPrecision))
            {//參數有改變才需要重新畫mesh
                Mesh newMesh = Create(radius, startAngleDegree, angleDegree);
                if (newMesh != null)
                {
                    cacheMesh = newMesh;
                    this.radius = radius;
                    this.startAngleDegree = startAngleDegree;
                    this.angleDegree = angleDegree;
                }
            }
            return cacheMesh;
        }

        private Vector3 CalcPoint(float angle)
        {//這個函數計算了非特殊角度射線在正方形上的點
            angle = angle % 360;
            if (angle == 0) {
                return new Vector3 (1, 0, 0);
            } else if (angle == 180) {
                return new Vector3(-1,0,0);
            }
            //這裏分別對應這個射線處於上圖哪個三角形中, 分別計算
            if (angle <= 45 || angle > 315) {
                return new Vector3(1,Mathf.Tan(Mathf.Deg2Rad*angle), 0);
            } else if (angle <= 135) {
                return new Vector3(1/Mathf.Tan(Mathf.Deg2Rad*angle), 1, 0);
            } else if (angle <= 225) {
                return new Vector3(-1, -Mathf.Tan(Mathf.Deg2Rad*angle), 0);
            } else {
                return new Vector3(-1/Mathf.Tan(Mathf.Deg2Rad*angle), -1, 0);
            }
        }

        private Mesh Create(float radius, float startAngleDegree, float angleDegree)
        {
            if (startAngleDegree == 360) {
                startAngleDegree = 0;
            }
            Mesh mesh = new Mesh();
            List<Vector3> calcVertices = new List<Vector3> ();
            calcVertices.Add (Vector3.zero);//第一個點是圓心點
            calcVertices.Add (CalcPoint (startAngleDegree));//第二個點是起始角度對應的點

            float [] specialAngle = new float[]{45, 135, 225, 315};//上圖正方形4個頂點對應的角度和點
            Vector3 [] specialPoint = new Vector3[] {new Vector3(1,1,0), 
                new Vector3(-1,1,0), 
                new Vector3(-1,-1,0),
                new Vector3(1,-1,0)};
            //計算正方形四個點是不是在要畫的扇形範圍內, 如果是, 則是要畫出來的頂點
            for (int i = 0; i < specialAngle.Length; ++i) {
                if(startAngleDegree < specialAngle[i] && specialAngle[i] - startAngleDegree < angleDegree)
                {
                    calcVertices.Add(specialPoint[i]);
                }
            }
            //這裏爲什麼要第二個for循環? 扇形的角度+起始角度就可能超過360, 所以要計算到720
            for (int i = 0; i < specialAngle.Length; ++i) {
                if(startAngleDegree < specialAngle[i]+360 && specialAngle[i]+360 - startAngleDegree < angleDegree)
                {
                    calcVertices.Add(specialPoint[i]);
                }
            }
            calcVertices.Add (CalcPoint (startAngleDegree + angleDegree));

            Vector3[] vertices = new Vector3[calcVertices.Count];

            //uv是網格上的點對應到紋理上的某個位置的像素, 紋理是一張圖片, 所以是二維
            Vector2[] uvs = new Vector2[vertices.Length];

            for (int i = 0; i < vertices.Length; ++i) {
                //之前是按半徑爲單位長度1計算的頂點, 實際頂點是要算上實際半徑
                vertices[i] = calcVertices[i]*radius;
                //紋理的半徑就是0.5, 圓心在0.5f, 0.5f的位置
                uvs[i] = new Vector2(calcVertices[i].x*0.5f+0.5f,calcVertices[i].y*0.5f+0.5f);
            }

            int[] triangles = new int[(vertices.Length-2)*3];
            for (int i = 0, vi = 1; i < triangles.Length; i += 3, vi++)
            {//每個三角形都是由圓心點+兩個相鄰弧度上的點構成的
                triangles[i] = 0;
                triangles[i + 2] = vi;
                triangles[i + 1] = vi + 1;
            }           
            mesh.vertices = vertices;
            mesh.triangles = triangles;
            mesh.uv = uvs;

            return mesh;
        }

        private bool checkDiff(float radius, float startAngleDegree, float angleDegree, int angleDegreePrecision, int radiusPrecision)
        {
            return (int)(startAngleDegree - this.startAngleDegree) != 0 || (int)((angleDegree - this.angleDegree) * angleDegreePrecision) != 0 ||
                (int)((radius - this.radius) * radiusPrecision) != 0;
        }
    }
}

最終效果: