﻿Shader "Quantum/Particle Mesh"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
		_Size ("Size", Range(0, 1)) = 0.01
	}
	SubShader
	{
		Tags { "RenderType"="Transparent"  "Queue"="Transparent" }
		LOD 100

		Pass
		{
			Blend SrcAlpha OneMinusSrcAlpha
			ZWrite Off
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma geometry geom
			#pragma multi_compile_fog

			#include "UnityCG.cginc"

			struct appdata
			{
				float4 pos : POSITION;
				float2 uv : TEXCOORD0;
			};

			struct v2g
			{
				float2 uv : TEXCOORD0;
				UNITY_FOG_COORDS(1)
				float4 pos : SV_POSITION;
			};

			struct g2f
			{
				float2 uv : TEXCOORD0;
				float4 pos : SV_POSITION;
				float4 wPos : NORMAL;
				float4 center : COLOR;
			};

			sampler2D _MainTex;
			float4 _MainTex_ST;

			v2g vert (appdata v)
			{
				v2g o;
				o.pos =v.pos;
				o.uv = TRANSFORM_TEX(v.uv, _MainTex);
				UNITY_TRANSFER_FOG(o,o.pos);
				return o;
			}

			float _Size;
			#define SQRT3 1.7320508075688772935274463415059

			[maxvertexcount(3)]
			void geom(triangle v2g IN[3], inout TriangleStream<g2f> tristream){
				g2f o;
				float4 c = (IN[0].pos + IN[1].pos + IN[2].pos)/3.0;
				o.wPos = float4(float2(-SQRT3, -1.0)*_Size, 0.0, 0.0);
				o.pos = mul(UNITY_MATRIX_P, mul(UNITY_MATRIX_MV, c) + o.wPos);
				o.uv = IN[0].uv;
				o.center = c;
				tristream.Append(o);
				o.wPos = float4(float2(0.0, 2.0)*_Size, 0.0, 0.0);
				o.pos = mul(UNITY_MATRIX_P, mul(UNITY_MATRIX_MV, c) + o.wPos);
				o.uv = IN[1].uv;
				o.center = c;
				tristream.Append(o);
				o.wPos = float4(float2(SQRT3, -1.0)*_Size, 0.0, 0.0);
				o.pos = mul(UNITY_MATRIX_P, mul(UNITY_MATRIX_MV, c) + o.wPos);
				o.uv = IN[2].uv;
				o.center = c;
				tristream.Append(o);
				tristream.RestartStrip();
			}

			fixed4 frag (g2f i) : SV_Target
			{
				// sample the texture
				fixed4 col = tex2D(_MainTex, i.uv);
				// apply fog
				UNITY_APPLY_FOG(i.fogCoord, col);
				float dist = length(i.wPos.xy);
				dist = clamp(_Size*_Size/dist-_Size, 0.0, 1.0);
				return float4(col.xyz, dist);
			}
			ENDCG
		}
	}
}
