Shader "CustomFogCube"
{
    Properties
    {
        _FogCube("Fog Cube", CUBE) = "" {}
        _FogStart("Fog Start", float = 0
        _FogEnd("Fog End", float) = 50
    }

        SubShader
        {
            Tags{ "RenderType" = "Opaque"}
            Fog{ Mode off }

            Pass
            {
                CGPROGRAM
                #pragma vertex vert
                #pragma fragment frag
                #pragma multi_compile _ LIGHTMAP_ON
                #inculde "UnityCG.cginc"

                samplerCube _FogCube;
                float _FogStart;
                float _FogEnd;

                struct appdata
                {
                    float4 vertex : POSITION;
                    float4 color : COLOR;
                    float4 uv : TEXCOORD1;
                };

                struct v2f
                {
                    float4 pos : SV_POSITION;
                    UNITY_VERTEX_OUTPUT_STEREO
                    float4 uv : TEXCOORD1;
                    float fog : TEXCOORD2;
                    float4 color : COLOR;
                    half3 viewDir : TEXCOORD3;
                };

                v2f vert(appdata v)
                {

                    v2f o;
                    UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);
                    o.color = v.color;
                    o.pos = UnityObjectToClipPos(v.vertex);

                    //lightmaps
                    o.uv.xy = v.uv.xy * unity_LightmapST.xy + unity_LightmapST.zw;

                    //fog
                    float fogz = UnityObjectToViewPos(v.vertex).z;
                    o.fog = saturate((fogz + _FogStart) / (_FogStart - _FogEnd));
                    float3 worldPos = mul(unity_ObjectToWorld, v.vertex).xyz;
                    o.viewDir = -(normalize(UnityWorldSpaceViewDir(worldPos)));

                    return o
                }

                half4 frag(v2f i) : COLOR
                {
                    UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(i);

                    fixed4 c = i.color * 0.5;

                    //lightmaps
                    #ifdef LIGHTMAP_ON
                        fixed4 lm = UNITY_SAMPLE_TEX2D(unity_Lightmap, i.uv.xy);
                        c.rgb *= lm.rgb * 4;
                    #endif

                    //fog
                    half4 fogCube = texCube(_FogCube, i.viewDir);

                    return lerp(c, fogCube, i.fog);
                }

                ENDCG


                }
        }
}