ScreenMaterial.cs

//Calico post processing with stencil mask
// https://twitter.com/CalicoGame/status/1121221295536951296

using System;
using UnityEngine;
using UnityEngine.Rendering;

[ExecuteInEditMode, ImageEffectAllowedInSceneView]
public class ScreenMaterialCommandBuffer : MonoBehaviour
{
    public enum Mode
    {
        Stencil,
        RenderTexture
    }

    public Mode RenderMode;

    public DepthTextureMode DepthMode = DepthTextureMode.None;

    //AfterForwardAlpha will work for most effects
    public CameraEvent RenderOrder = CameraEvent.AfterForwardAlpha;
    public Material EffectMaterial;

    private CameraEvent _cameraEvent;

    private CommandBuffer _commandBuffer;

//    [SerializeField]
    private string GlobalRenderTextureName = "_MappedNoise";
    private int _globalRenderTextureName;


    private Camera _camera;

    private Camera Camera
    {
        get
        {
            if (_camera == null)
                _camera = GetComponent<Camera>();

            return _camera;
        }
    }

    //Update settings when edited
    private void OnValidate()
    {
        _globalRenderTextureName = Shader.PropertyToID(GlobalRenderTextureName);
        Camera.depthTextureMode = DepthMode;

        if (RenderOrder != _cameraEvent && _commandBuffer != null)
        {
            Camera.RemoveCommandBuffer(_cameraEvent, _commandBuffer);
            Camera.AddCommandBuffer(RenderOrder, _commandBuffer);
            _cameraEvent = RenderOrder;
        }
        else if (RenderOrder != _cameraEvent && EffectMaterial != null)
        {
            OnEnable();
        }
    }

    private void BlitMaterialToRenderTexture()
    {
        if (_commandBuffer != null || EffectMaterial == null)
            return;

        var _previousTarget = BuiltinRenderTextureType.CurrentActive;
        _commandBuffer = new CommandBuffer { name = "Blit Material to Render Texture" };

        var downsampler = (int) Mathf.Pow(2, 1);
        var tempRenderTexture = Shader.PropertyToID("_tempRenderTex");

        _commandBuffer.GetTemporaryRT(tempRenderTexture, _camera.pixelWidth / downsampler, _camera.pixelHeight / downsampler, 0);

        _commandBuffer.SetRenderTarget(tempRenderTexture);
        _commandBuffer.ClearRenderTarget(true, true, Color.clear, 1f);
//        _commandBuffer.Blit(BuiltinRenderTextureType.CameraTarget, tempRenderTexture);
//        _commandBuffer.SetGlobalTexture("_MainTex", tempRenderTexture);
        _commandBuffer.Blit(BuiltinRenderTextureType.CameraTarget, tempRenderTexture, EffectMaterial);

        _commandBuffer.SetGlobalTexture(GlobalRenderTextureName, tempRenderTexture);


        _commandBuffer.SetRenderTarget(_previousTarget);
//        _commandBuffer.Blit(_globalRenderTex, BuiltinRenderTextureType.CameraTarget);
        Camera.AddCommandBuffer(RenderOrder, _commandBuffer);
    }

    private void OnEnable()
    {
        switch (RenderMode)
        {
            case Mode.Stencil:
                BlitMaterialToCameraTarget();
                break;
            case Mode.RenderTexture:
                BlitMaterialToRenderTexture();
                break;
            default:
                throw new ArgumentOutOfRangeException();
        }
    }

    private void BlitMaterialToCameraTarget()
    {
        if (_commandBuffer != null || EffectMaterial == null)
            return;

        _commandBuffer = new CommandBuffer { name = "Blit with Replacement Material" };

        // 1: Get a render texture by the name defined in the inspector at screen size and clear it
        var tempRenderTexture = Shader.PropertyToID("_tempRenderTex");
        _commandBuffer.GetTemporaryRT(tempRenderTexture, -1, -1, 0);
        _commandBuffer.SetRenderTarget(tempRenderTexture, tempRenderTexture);
        _commandBuffer.ClearRenderTarget(true, true, Color.clear);

        // 2: Blit the camera target into the temporary render texture
        _commandBuffer.Blit(BuiltinRenderTextureType.CameraTarget, tempRenderTexture);
        // 3: Active render target is now tempRenderTexture

        // 4: Set _MainTex as the temporary render texture
        _commandBuffer.SetGlobalTexture("_MainTex", tempRenderTexture);

        // 5: Blit the camera target again, but this time using a replacement material
        _commandBuffer.Blit(BuiltinRenderTextureType.CameraTarget, BuiltinRenderTextureType.CameraTarget, EffectMaterial);

        Camera.AddCommandBuffer(RenderOrder, _commandBuffer);
    }

    private void OnDisable()
    {
        if (_commandBuffer == null)
            return;
        Camera.RemoveCommandBuffer(RenderOrder, _commandBuffer);
        _commandBuffer = null;
    }
}