Shader "Custom/Limiter" {
Properties
{
    _MainTex ("Texture", 2D) = "white" {}
    _PalTex ("Pallete", 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;
        };

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

        sampler2D _MainTex;
        sampler2D _PalTex;

        fixed4 frag (v2f i) : SV_Target
        {
            float4 baseCol = tex2D(_MainTex, i.uv);
            float4 palCol = tex2D(_PalTex, 0);
            float palDiff = 1000;

            for (int p = 4; p < 8; p++) {
                float baseColDiff = abs(tex2D(_PalTex, p).r - baseCol.r) + abs(tex2D(_PalTex, p).g - baseCol.g) + abs(tex2D(_PalTex, p).b - baseCol.b);
                palDiff = min(palDiff, baseColDiff);
                palCol = (abs(palDiff - baseColDiff) < 0.001) ? tex2D(_PalTex, p) : palCol;
            }

            return palCol;
        }
        ENDCG
    }
}
}