[Unity] fixed legacy blur effect from Unity Standard Assets for single pass stereo

https://assetstore.unity.com/packages/essentials/legacy-image-effects-83913

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityStandardAssets.ImageEffects;

[ExecuteInEditMode]
[RequireComponent(typeof(Camera))]
[AddComponentMenu("Image Effects/Blur/Blur (Optimized) Stereo")]
public class BlurOptimizedStereo : PostEffectsBase
{

    [Range(0, 2)]
    public int downsample = 1;

    public enum BlurType
    {
        StandardGauss = 0,
        SgxGauss = 1,
    }

    [Range(0.0f, 10.0f)]
    public float blurSize = 3.0f;

    [Range(1, 4)]
    public int blurIterations = 2;

    public BlurType blurType = BlurType.StandardGauss;

    public Shader blurShader = null;
    private Material blurMaterial = null;

    private Material bypassStereoMaterial = null;
    private Shader bypassStereoShader = null;
    public override bool CheckResources()
    {
        CheckSupport(false);
        if(blurShader == null)
        {
            blurShader = Shader.Find("Hidden/FastBlur");
        }
        blurMaterial = CheckShaderAndCreateMaterial(blurShader, blurMaterial);
        if (bypassStereoMaterial == null)
        {
            bypassStereoShader = Shader.Find("Hidden/BypassStereoImageEffectShader");
            bypassStereoMaterial = new Material(bypassStereoShader);
        }
        if (!isSupported)
            ReportAutoDisable();
        return isSupported;
    }

    public void OnDisable()
    {
        if (blurMaterial)
            DestroyImmediate(blurMaterial);
    }

    public void OnRenderImage(RenderTexture source, RenderTexture destination)
    {
        if (CheckResources() == false)
        {
            Graphics.Blit(source, destination);
            return;
        }

        float widthMod = 1.0f / (1.0f * (1 << downsample));

        blurMaterial.SetVector("_Parameter", new Vector4(blurSize * widthMod, -blurSize * widthMod, 0.0f, 0.0f));
        source.filterMode = FilterMode.Bilinear;

        int rtW = source.width >> downsample;
        int rtH = source.height >> downsample;

        // downsample
        RenderTexture rt = RenderTexture.GetTemporary(rtW, rtH, 0, source.format);

        rt.filterMode = FilterMode.Bilinear;
        Graphics.Blit(source, rt, blurMaterial, 0);

        var passOffs = blurType == BlurType.StandardGauss ? 0 : 2;

        for (int i = 0; i < blurIterations; i++)
        {
            float iterationOffs = (i * 1.0f);
            blurMaterial.SetVector("_Parameter", new Vector4(blurSize * widthMod + iterationOffs, -blurSize * widthMod - iterationOffs, 0.0f, 0.0f));

            // vertical blur
            RenderTexture rt2 = RenderTexture.GetTemporary(rtW, rtH, 0, source.format);
            rt2.filterMode = FilterMode.Bilinear;
            Graphics.Blit(rt, rt2, blurMaterial, 1 + passOffs);
            RenderTexture.ReleaseTemporary(rt);
            rt = rt2;

            // horizontal blur
            rt2 = RenderTexture.GetTemporary(rtW, rtH, 0, source.format);
            rt2.filterMode = FilterMode.Bilinear;
            Graphics.Blit(rt, rt2, blurMaterial, 2 + passOffs);
            RenderTexture.ReleaseTemporary(rt);
            rt = rt2;
        }

        Graphics.Blit(rt, destination, bypassStereoMaterial);

        RenderTexture.ReleaseTemporary(rt);
    }
}


Shader "Hidden/BypassStereoImageEffectShader"
{
 Properties
 {
  _MainTex ("Texture", 2D) = "white" {}
 }
 SubShader
 {
  // No culling or depth
  Cull Off ZWrite Off ZTest Always

  Pass
  {
   CGPROGRAM
   #pragma vertex vert
   #pragma fragment frag
   
   #include "UnityCG.cginc"

   struct appdata
   {
    float4 vertex : POSITION;
    float2 uv : TEXCOORD0;
   };

   struct v2f
   {
    float2 uv : TEXCOORD0;
    float4 vertex : SV_POSITION;
   };


   sampler2D _MainTex;
   float4 _MainTex_ST;

   v2f vert (appdata v)
   {
    v2f o;
    o.vertex = UnityObjectToClipPos(v.vertex);
    //o.uv = v.uv;
    o.uv = UnityStereoScreenSpaceUVAdjust(v.uv, _MainTex_ST);
    return o;
   }


   fixed4 frag (v2f i) : SV_Target
   {
#if UNITY_SINGLE_PASS_STEREO
    if (unity_StereoEyeIndex == 0)//left eye
    {
     i.uv.x = i.uv.x * 0.5;
    }
    else//right eye
    {
     i.uv.x = i.uv.x * 0.5 + 0.5;
    }
#endif
    fixed4 col = tex2D(_MainTex, i.uv);
    return col;
   }
   ENDCG
  }
 }
}