// http://www.iquilezles.org/www/articles/dynclouds/dynclouds.htm

Shader "WindComposite"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
	}
	SubShader
	{
		Tags { "RenderType"="Opaque" }
		LOD 100

		Pass
		{
			CGPROGRAM

			#pragma vertex vert_imgMy
            #pragma fragment frag
			
			#include "UnityCG.cginc"

			sampler2D _MainTex;
			float4 _MainTex_ST;

			float3 _AtgWindDir;
			float2 _AtgWindUVs;
			float2 _AtgWindUVs1;
			float2 _AtgWindUVs2;
			float2 _AtgWindUVs3;
			float2 _AtgGust;

			struct appdata_imgMy
			{
				float4 vertex : POSITION;
				half2 texcoord : TEXCOORD0;
			};

			struct v2f_imgMy
			{
				float4 pos : SV_POSITION;
				half2 uv : TEXCOORD0;
			};


			v2f_imgMy vert_imgMy( appdata_imgMy v )
			{
				v2f_imgMy o;
				o.pos = UnityObjectToClipPos (v.vertex);
				o.uv = v.texcoord;
				return o;
			}

			half4 frag(v2f_imgMy i) : SV_Target {

				half4 n1 = tex2D(_MainTex, i.uv + _AtgWindUVs);
				half4 n2 = tex2D(_MainTex, i.uv + _AtgWindUVs1); 
				half4 n3 = tex2D(_MainTex, i.uv + _AtgWindUVs2);
				half4 n4 = tex2D(_MainTex, i.uv * _AtgGust.x + _AtgWindUVs3);

				half4 sum = half4(n1.r, n1.g + n2.g, n1.b + n2.b + n3.b, n1.a + n2.a + n3.a + n4.a);
				const half4 weights = half4(0.5000, 0.2500 , 0.1250 , 0.0625 );
				
				half2 WindStrengthGustNoise;
				WindStrengthGustNoise.x = dot(sum, weights);		// WindStrength
				WindStrengthGustNoise.y = (n4.a + n2.a ) * 0.5f;	// GrassGustNoise

			//	Sharpen WindStrengthGustNoise according to turbulence
				WindStrengthGustNoise = ( WindStrengthGustNoise - half2(0.5, 0.5) ) * _AtgGust.y + half2(0.5, 0.5);

				return half4(
					WindStrengthGustNoise,
					1,
					0
				);
			}
			ENDCG
		}
	}
}