How to Get Screen's DepthBuffer and Set it as A RenderTexture's DepthBuffer?

Graphics
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How to Get Screen’s DepthBuffer and Set it as A RenderTexture’s DepthBuffer?

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I’d just make your main camera the parent of another camera with the same settings with this script on it to render the depth to a RenderTexture. You could also render from your main camera to a RenderTexture and then set the RenderTexture target to null once per frame but I feel like this is a much simpler solution.

using UnityEngine;
using System.Collections;

public class RenderDepthTexture : MonoBehaviour {

    private Camera camera;

    // Use this for initialization
    void Start () {
        camera = GetComponent<Camera> ();
        camera.depthTextureMode = DepthTextureMode.Depth;
    }
}
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int myRT = Shader.PropertyToID("myRT");
mytestcb.GetTemporaryRT(myRT, -1, -1);
mytestcb.SetRenderTarget(myRT, BuiltinRenderTextureType.Depth);

Warning:
CommandBuffer: built-in render texture type 3 not found while executing mytestcb (SetRenderTarget depth buffer)

What’s the Warning Message Meaning.How to resolve it.