using UnityEngine;
using System.Collections;
[ExecuteInEditMode]
public class Polygon : MonoBehaviour
{

    public Material mat; //绑定材质
    Vector3[] worldPos; //存储获取的3D坐标
    Vector4[] screenPos; //存储待绘制的多边形顶点屏幕坐标
    int maxPointNum = 99;  //多边形顶点总数
    public int currentpointNum = 0; //当前已经获得的顶点数
    public int pointNum2Shader = 0; //传递顶点数量给shader
    public bool InSelection = true; //是否处于顶点获取过程

    void Start()
    {
        worldPos = new Vector3[maxPointNum];
        screenPos = new Vector4[maxPointNum];
    }


    void Update()
    {
        mat.SetVectorArray("Value", screenPos); //传递顶点屏幕位置信息给shader
        mat.SetInt("PointNum", pointNum2Shader); //传递顶点数量给shader

        //使用摄像机发射一条射线，以获取要选择的3D位置
        Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
        RaycastHit hit;
        if (Physics.Raycast(ray, out hit, 100))
        {
            Debug.DrawLine(ray.origin, hit.point);
        }


        //利用鼠标点击来获取位置信息
        if (Input.GetMouseButtonDown(0) && InSelection)
        {
            if (currentpointNum < maxPointNum)
            {
                currentpointNum++;
                pointNum2Shader++;
                worldPos[currentpointNum - 1] = hit.point;
                Vector3 v3 = Camera.main.WorldToScreenPoint(worldPos[currentpointNum - 1]);
                screenPos[currentpointNum - 1] = new Vector4(v3.x, Screen.height - v3.y, v3.z, 0);
                //Debug.Log($"screenPos=={screenPos[currentpointNum - 1]}");
                //Debug.Log($"currentpointNum=={currentpointNum}");
            }
            else
            {
                InSelection = false;
            }
        }

        //实时更新已选择的3D点的屏幕位置
        for (int i = 0; i < maxPointNum; i++)
        {
            Vector3 v3 = Camera.main.WorldToScreenPoint(worldPos[i]);
            screenPos[i] = new Vector4(v3.x, Screen.height - v3.y, v3.z, 0);

        }

        //检测是否有3D点移动到了摄像机后面，如果有，则停止绘制
        for (int i = 0; i < currentpointNum; i++)
        {
            if (Vector3.Dot(worldPos[i] - Camera.main.transform.position, Camera.main.transform.forward) <= 0)
            {
                pointNum2Shader = 0;
                break;
            }
            pointNum2Shader = currentpointNum;
        }
    }

    //抓取当前的渲染图像进行处理
    void OnRenderImage(RenderTexture src, RenderTexture dest)
    {
        Graphics.Blit(src, dest, mat);
    }
}