Shader "TA/Snow"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _AddTex ("AddTex",2D) = "white" {}
        _BumpMap("BumpMap",2D)= "white" {}
        _SnowStep(" Snow",Range(0,1))=0.5
        _LightDir("LightDir",vector) = (0,0,1,1)
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            // make fog work
            #pragma multi_compile_fog
            
            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
                half3 vnormal : NORMAL;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
                fixed3 normal : NORMAL;
            };

            sampler2D _MainTex,_AddTex,_BumpMap;
            fixed _SnowStep;
            half4 _MainTex_ST,_LightDir;
            
            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                o.normal = v.vnormal;
                UNITY_TRANSFER_FOG(o,o.vertex);

                return o;
            }
            
            fixed4 frag (v2f i) : SV_Target
            {
                fixed4 s = tex2D(_AddTex, i.uv);
                half3 customColor = step(1-_SnowStep*s.a,i.normal.y);
                fixed4 col = tex2D(_MainTex, i.uv);
                fixed3 bum = UnpackNormal(tex2D(_BumpMap, i.uv) * _LightDir.w);
                half sDir = max(0,dot(_LightDir,bum));
                
                // apply fog
                UNITY_APPLY_FOG(i.fogCoord, col);
                return half4((col.rgb*sDir + customColor*s*0.7),1);
            }
            ENDCG
        }
    }
}