public class MainCameraShader : MonoBehaviour {

        public Material m_DepthMaterial;
        // Use this for initialization
        void Start () {
            
        }
        
        // Update is called once per frame
        void Update () {
            

        }
        void OnRenderImage(RenderTexture src, RenderTexture dest)
        {

            Graphics.Blit(src, dest,m_DepthMaterial);
        }



    } ## 给上面的代码加上shader 
    Shader "Custom/DepthMap" {
        SubShader{
            Tags{ "RenderType" = "Opaque" }

            Pass
            {

                ZTest Always Cull Off ZWrite Off

                CGPROGRAM

                // Use shader model 3.0 target, to get nicer looking lighting
                #pragma glsl
                #pragma fragmentoption ARB_precision_hint_fastest
                #pragma target 3.0
                #pragma vertex vert
                #pragma fragment frag
                #include "unityCG.cginc"
                sampler2D _CameraDepthTexture;

                struct v2f 
                {
                    float4 pos : SV_POSITION;
                    float4 scrPos:TEXCOORD0;
                };
                //Vertex Shader
                v2f vert(appdata_base v) 
                {
                    v2f o;
                    o.pos = UnityObjectToClipPos(v.vertex);
                    o.scrPos = ComputeScreenPos(o.pos);
                    return o;
                }

                //Fragment Shader
                float4 frag(v2f i) :COLOR
                {
                    float depthValue = 1 - Linear01Depth(tex2Dproj(_CameraDepthTexture, UNITY_PROJ_COORD(i.scrPos)).r);

                    int ar, ag, ab;
                    ar = depthValue * 0x1000000;
                    ag = ar % 65536;
                    ab = ar % 256;
                    ar /= 65536;
                    ag /= 256;

                    float dv = ab + ag * 256 + ar * 65536;
                    dv /= 0x1000000;
                    return float4(ar/256.0f, ag/256.0f, ab/256.0f, 1.0f);

                }
                
                ENDCG
            }
        }
            FallBack "Diffuse"
    }