Shader "Custom/URP_SimpleBlurShader"
{
    Properties {
        _Size ("Blur", Range(0, 30)) = 1
        [HideInInspector] _MainTex ("Texture (RGB)", 2D) = "white" {}
    }
    SubShader {
        Tags { "Queue"="Transparent" "RenderType"="Transparent" }
        LOD 100
        ZWrite Off
        Blend SrcAlpha OneMinusSrcAlpha

        Pass {
            Name "FORWARD"
            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_fog
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

            struct Attributes {
                float4 positionOS : POSITION;
                float2 uv         : TEXCOORD0;
                float4 color      : COLOR;
            };

               struct Varyings {
                   float4 positionHCS : SV_POSITION;
                   float2 uv          : TEXCOORD0;
                   float4 color       : COLOR;
                   float fogFactor    : TEXCOORD1;
               };

            CBUFFER_START(UnityPerMaterial)
                float _Size;
            CBUFFER_END

            TEXTURE2D(_MainTex); SAMPLER(sampler_MainTex);
            TEXTURE2D(_CameraOpaqueTexture); SAMPLER(sampler_CameraOpaqueTexture);
            float4 _MainTex_ST;

            Varyings vert(Attributes IN)
            {
                Varyings OUT;
                OUT.positionHCS = TransformObjectToHClip(IN.positionOS.xyz);
                OUT.uv = TRANSFORM_TEX(IN.uv, _MainTex);
                OUT.color = IN.color;
                OUT.fogFactor = ComputeFogFactor(OUT.positionHCS.z / OUT.positionHCS.w);
                return OUT;
            }

            float4 frag(Varyings IN) : SV_Target
            {
                float2 uv = IN.uv;
                float alpha = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, uv).a * IN.color.a;
                float2 texelSize = float2(1.0/_ScreenParams.x, 1.0/_ScreenParams.y);
                float4 sum = float4(0,0,0,0);

                // Horizontal blur
                sum += SAMPLE_TEXTURE2D(_CameraOpaqueTexture, sampler_CameraOpaqueTexture, uv + float2(-4.0, 0.0) * texelSize * _Size * alpha) * 0.05;
                sum += SAMPLE_TEXTURE2D(_CameraOpaqueTexture, sampler_CameraOpaqueTexture, uv + float2(-3.0, 0.0) * texelSize * _Size * alpha) * 0.09;
                sum += SAMPLE_TEXTURE2D(_CameraOpaqueTexture, sampler_CameraOpaqueTexture, uv + float2(-2.0, 0.0) * texelSize * _Size * alpha) * 0.12;
                sum += SAMPLE_TEXTURE2D(_CameraOpaqueTexture, sampler_CameraOpaqueTexture, uv + float2(-1.0, 0.0) * texelSize * _Size * alpha) * 0.15;
                sum += SAMPLE_TEXTURE2D(_CameraOpaqueTexture, sampler_CameraOpaqueTexture, uv) * 0.18;
                sum += SAMPLE_TEXTURE2D(_CameraOpaqueTexture, sampler_CameraOpaqueTexture, uv + float2(1.0, 0.0) * texelSize * _Size * alpha) * 0.15;
                sum += SAMPLE_TEXTURE2D(_CameraOpaqueTexture, sampler_CameraOpaqueTexture, uv + float2(2.0, 0.0) * texelSize * _Size * alpha) * 0.12;
                sum += SAMPLE_TEXTURE2D(_CameraOpaqueTexture, sampler_CameraOpaqueTexture, uv + float2(3.0, 0.0) * texelSize * _Size * alpha) * 0.09;
                sum += SAMPLE_TEXTURE2D(_CameraOpaqueTexture, sampler_CameraOpaqueTexture, uv + float2(4.0, 0.0) * texelSize * _Size * alpha) * 0.05;

                sum.rgb = MixFog(sum.rgb, IN.fogFactor);
                return sum;
            }
            ENDHLSL
        }
    }
}