Shader "CrispyPin/gol"
{
    Properties
    {
        _LastFrame ("Texture", 2D) = "white" {}
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        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 _LastFrame;

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

            int state(half2 uv, half x, half y){
                return tex2D(_LastFrame, uv + half2(x, y)).r > 0;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                const half d = 1.0/256.0;

                int count = state(i.uv, -d, -d)+
                    state(i.uv, 0, -d)+
                    state(i.uv, d, -d)+
                    state(i.uv, -d, 0)+
                    state(i.uv, d, 0)+
                    state(i.uv, -d, d)+
                    state(i.uv, 0, d)+
                    state(i.uv, d, d);
                half this = tex2D(_LastFrame, i.uv).r;
                half state;

                if (this.r > 0){
                    state = count > 1 && count < 4;
                    // col = count > 0 && count < 6; // mazetric
                }
                else {
                    state = count == 3;
                }

                float4 col = float4(i.uv * state, 0.5 * state, 1);
                return col;
            }
            ENDCG
        }
    }
}