Unity CPU 中使用深度

Unity CPU 中使用深度贴图

大多数文章讲的都是在gpu中使用深度贴图 我记忆一下在CPU 中使用深度贴图。
我们今天利用深度贴图计算出世界坐标 。

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前言

有射线的时候可以直接根据射线求出世界坐标。 如果没有包围盒子就很难根据鼠标输入求出世界坐标

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一、把GPU中的深度贴图取出来

参考这个文章

     depthRT = new RenderTexture(Width, Height, 16, RenderTextureFormat.Depth);
     depthRT.name = "MainDepthBuffer";
     ///深度值 用 单通道  16bit 存起来
     depthTex = new RenderTexture(Width, Height, 0, RenderTextureFormat.R16);
     depthTex.name = "SceneDepthTex";
     _cbDepth = new CommandBuffer();
    _cbDepth.name = "CommandBuffer_DepthBuffer";
    ///得将深度贴图拷贝到一个 rendertexture 里面
    _cbDepth.Blit(depthRT.depthBuffer, depthTex.colorBuffer);

二、将根据鼠标输入取出RenderTexture里面的像素

      //将深度rendertexture拷贝到 texture2d
      myTexture = new Texture2D(Width, Height, TextureFormat.R16, false);
       RenderTexture.active = depthTex;

       Vector2 tmpPos = Input.mousePosition;

       int posX = Mathf.CeilToInt(tmpPos.x);
       int posY = Mathf.CeilToInt(tmpPos.y);

       myTexture.ReadPixels(new Rect(0, 0, Screen.width, Screen.height), 0, 0);
       myTexture.Apply();
       //取出某一个点的像素 r 通道即为 深度值
       Color tmpColor = myTexture.GetPixel(posX, posY);

三、求出距离相机的距离

根据这个文章

    float  CaculateZ( float d)
    {
         ///由于 DX 平台需要取反   有些平台不需要 
        float result = 1-d;

        float tmpMinus = _Camera.nearClipPlane - _Camera.farClipPlane   ;
        float tmpMuti = _Camera.farClipPlane * _Camera.nearClipPlane;
        result = ((tmpMinus * result) / tmpMuti) + (1.0f / _Camera.nearClipPlane);
        result = 1.0f / result;

        return result;
     }

四、算出世界坐标

     Vector3 screenPos = Input.mousePosition;
     float tmpZ = CaculateZ(tmpColor.r);
    
     screenPos.z = tmpZ ;

     Vector3 worldPos= Camera.main.ScreenToWorldPoint(screenPos);

Camera.main.ScreenToWorldPoint 这个输入值 Z 值表示距离 相机的距离 才能得到正确的 世界坐标。

可以使用另外一种方式算出世界坐标：
在相机前面摆一个 平面 ，然后用射线找到输入点的世界坐标

    void CaculateScreenDepth(float z)
    {

        Vector3 tmpZ = new Vector3(0, 0, z + _Camera.transform.position.z);
        Plane plane = new Plane(-Vector3.forward, tmpZ);

        Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
        float dist;
        if (plane.Raycast(ray, out dist))
        {
            Vector3 P = ray.GetPoint(dist);

            Debug.Log("p==" + P);

            GameObject tmpObj = GameObject.CreatePrimitive(PrimitiveType.Sphere);
            tmpObj.transform.localScale = Vector3.one * 0.1f;

            tmpObj.transform.position = P;
        }


    }

两种方式等价。

五、全部代码

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

public class TestDepth : MonoBehaviour
{

    private RenderTexture depthRT;
    private RenderTexture colorRT;
    private RenderTexture depthTex;

    private CommandBuffer _cbDepth = null;

    private Camera _Camera = null;

    public GameObject mainTexture;
    private void Awake()
    {
        _Camera = Camera.main;

        int Width =  Screen.width;
        int Height = Screen.height;

        _Camera.depthTextureMode = DepthTextureMode.Depth;

        depthRT = new RenderTexture(Width, Height, 16, RenderTextureFormat.Depth);
        depthRT.name = "MainDepthBuffer";
        colorRT = new RenderTexture(Width, Height, 0, RenderTextureFormat.ARGB32);
        colorRT.name = "MainColorBuffer";



        depthTex = new RenderTexture(Width, Height, 0, RenderTextureFormat.R16);
        depthTex.name = "SceneDepthTex";

        _cbDepth = new CommandBuffer();
        _cbDepth.name = "CommandBuffer_DepthBuffer";
        _cbDepth.Blit(depthRT.depthBuffer, depthTex.colorBuffer);

        
         myTexture = new Texture2D(Width, Height, TextureFormat.R16, false);
       // _cbDepth.Blit(depthTex.colorBuffer, myTexture);
        _Camera.AddCommandBuffer(CameraEvent.AfterDepthTexture, _cbDepth);

        mainTexture.GetComponent<Renderer>().material.mainTexture = myTexture;

    }

    float  CaculateZ( float d)
    {

        float result = 1-d;

        float tmpMinus = _Camera.nearClipPlane - _Camera.farClipPlane   ;
        float tmpMuti = _Camera.farClipPlane * _Camera.nearClipPlane;
        result = ((tmpMinus * result) / tmpMuti) + (1.0f / _Camera.nearClipPlane);


         result = 1.0f / result;

        return result;
     }

    Texture2D myTexture;
    private void Update()
    {
      

        if (Input.GetMouseButtonDown(0))
        {
          
            RenderTexture.active = depthTex;

            Vector2 tmpPos = Input.mousePosition;

            int posX = Mathf.CeilToInt(tmpPos.x);
            int posY = Mathf.CeilToInt(tmpPos.y);

            myTexture.ReadPixels(new Rect(0, 0, Screen.width, Screen.height), 0, 0);
            myTexture.Apply();

        
            Color tmpColor = myTexture.GetPixel(posX, posY);
        
   

            Vector3 screenPos = Input.mousePosition;
            float tmpZ = CaculateZ(tmpColor.r);
           
            screenPos.z = tmpZ ;

            Vector3 worldPos= Camera.main.ScreenToWorldPoint(screenPos);
           
        
          

        }

    }



    void OnPreRender()
    {
        _Camera.SetTargetBuffers(colorRT.colorBuffer, depthRT.depthBuffer);
    }

    private void OnPostRender()
    {
        //目前的机制不需要这次拷贝
        Graphics.Blit(colorRT, (RenderTexture)null);
    }



    void CaculateScreenDepth(float z)
    {

        Vector3 tmpZ = new Vector3(0, 0, z + _Camera.transform.position.z);
        Plane plane = new Plane(-Vector3.forward, tmpZ);

        Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
        float dist;
        if (plane.Raycast(ray, out dist))
        {
            Vector3 P = ray.GetPoint(dist);

            Debug.Log("p==" + P);

            GameObject tmpObj = GameObject.CreatePrimitive(PrimitiveType.Sphere);
            tmpObj.transform.localScale = Vector3.one * 0.1f;

            tmpObj.transform.position = P;
        }


    }



}