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;
				UNITY_VERTEX_INPUT_INSTANCE_ID
			};

			struct v2f
			{
				float2 uv : TEXCOORD0;
				float4 vertex : SV_POSITION;
				UNITY_VERTEX_OUTPUT_STEREO
			};

			sampler2D _LastFrame;

			v2f vert (appdata v)
			{
				v2f o;
				UNITY_SETUP_INSTANCE_ID(v);
				UNITY_INITIALIZE_OUTPUT(v2f, o);
				UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(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
		}
	}
}
