Shader "Hidden/DepthFog"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader
    {
        // No culling or depth
        Cull Off ZWrite Off ZTest Always

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

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

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

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv;
                return o;
            }

            sampler2D _MainTex;

            sampler2D _CameraDepthTexture;
            float _StartDistance,_EndDistance,_Height;
            fixed4 _FogCol;
            float4x4 _InvVP;
            fixed4 frag (v2f i) : SV_Target
            {
                fixed4 col = tex2D(_MainTex, i.uv);
                float depth = SAMPLE_DEPTH_TEXTURE(_CameraDepthTexture, i.uv);
                float4 proj = float4(i.uv.xy*2-1, depth, 1);
                float4 worldPos = mul(_InvVP, proj);
                worldPos.xyz /= worldPos.w;
                float ditance = length(worldPos.xyz - _WorldSpaceCameraPos.xyz);
                fixed fogFactor = smoothstep(_StartDistance, _EndDistance, ditance);
                fixed fogFactorHeigh = 1 - smoothstep(0, _Height, worldPos.y);
                fogFactor *= fogFactorHeigh;
                fixed3 finalCol = lerp(col.rgb, _FogCol, fogFactor* _FogCol.a);
                return fixed4(finalCol,1);
            }
            ENDCG
        }
    }
}