Graphics.Blit to copy material to texture gives incorrect results

Question

I have a material using a shader I wrote. I am using HDRP. This shader samples a texture, does some manipulation to the texture, and outputs the result.

I want to save the the result of this manipulation as a texture asset.

    public Material mat;
    public int width = 2048;
    public int height = 1024;
    public Texture2D tex;

    public Texture2D SaveMaterialToTexture(Material mat, int width, int height)
    {
        Texture2D tex = new Texture2D(width, height);
        RenderTexture rt = new RenderTexture(width, height, 0);
        RenderTexture.active = rt;
        Graphics.Blit(null, rt, mat, 0);
        tex.ReadPixels(new Rect(0, 0, width, height), 0, 0);
        tex.Apply();

        return tex;
    }

    public void SaveTexToDisk()
    {
        tex = SaveMaterialToTexture(mat, width, height);
        byte[] bytes = tex.EncodeToPNG();
        System.IO.File.WriteAllBytes(Application.dataPath + "/Tex.png", bytes);
    }

The appearance of the material and the outputted texture are not the same.

The sizes of the texture I am manipulating in my shader, and the size of the texture I am trying to save are set to the same.

I have made sure I am using an unlit shader, and not some sort of surface shader.

I have tried adding this as a tag to my SubShader "RenderTexture"="True"

I have tried using a pass like this Graphics.Blit(null, blitTarget, blitMaterial, 0);

I have tried with a different very simple unlit shader, outlined below, and the result seems to be correct.

fixed4 frag (v2f i) : SV_Target
{
   float4 col = tex2D(_MainTex, i.uv);
   return float4(col.r + i.uv.x, col.g + i.uv.y, col.b, 1.0);
}

Answer 1

Issue was using TexelSize in the shader it seems. Start manually feeding the TexelSize in my self, without using unity's built in shader property, and everything started to work.