Shader "Unlit/InnerSpriteOutline HLSL"
{
    Properties
    {
        _MainTex("Diffuse", 2D) = "white" {}
        _OutlineColor("Outline Color", Color) = (1,1,1,1)
    }

    HLSLINCLUDE
    #include "Packages/com.unity.render-pipelines.lightweight/ShaderLibrary/Core.hlsl"
    ENDHLSL

    SubShader
    {
        Tags {"Queue" = "Transparent" "RenderType" = "Transparent" "RenderPipeline" = "LightweightPipeline" }

        Blend SrcAlpha OneMinusSrcAlpha
        Cull Off
        ZWrite Off
        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;
           float4 _MainTex_TexelSize;

           fixed4 _OutlineColor;

           v2f vert(appdata v)
           {
               v2f o;
               o.vertex = UnityObjectToClipPos(v.vertex);
               o.uv = TRANSFORM_TEX(v.uv, _MainTex);
               return o;
           }

           fixed4 frag(v2f i) : SV_Target
           {
               fixed4 col = tex2D(_MainTex, i.uv);

               fixed leftPixel = tex2D(_MainTex, i.uv + float2(-_MainTex_TexelSize.x, 0)).a;
               fixed upPixel = tex2D(_MainTex, i.uv + float2(0, _MainTex_TexelSize.y)).a;
               fixed rightPixel = tex2D(_MainTex, i.uv + float2(_MainTex_TexelSize.x, 0)).a;
               fixed bottomPixel = tex2D(_MainTex, i.uv + float2(0, -_MainTex_TexelSize.y)).a;

               fixed outline = (1 - leftPixel * upPixel * rightPixel * bottomPixel) * col.a;

               return lerp(col, _OutlineColor, outline);
           }
           ENDCG
       }
    }
    Fallback "Hidden/Sprite-Fallback"
}