Demo 08 - Circle on terrain

Shader "Custom/CircleOnTerrain" {
    Properties {
        _MainTex ("Base (RGB)", 2D) = "white" {}
        _AreaColor ("Area Color", Color) = (1, 1, 1)
        _Center ("Center", Vector) = (0,0,0,0)
        _Radius ("Radius", Range(0, 500)) = 20
        _Border ("Border", Range(0, 100)) = 5
    }
    SubShader {
        Tags { "RenderType"="Opaque" }

        CGPROGRAM
        #pragma surface surf Lambert

        sampler2D _MainTex;
        fixed3 _AreaColor;
        float3 _Center;
        float _Border;
        float _Radius;

        struct Input {
            float2 uv_MainTex;
            float3 worldPos;
        };

        void surf (Input IN, inout SurfaceOutput o) {
            half4 c = tex2D (_MainTex, IN.uv_MainTex);
            float dist = distance(_Center, IN.worldPos);

            if(dist > _Radius && dist < (_Radius + _Border))
                o.Albedo = _AreaColor;
            else
                o.Albedo = c.rgb;

            o.Alpha = c.a;
        }
        ENDCG
    }
    FallBack "Diffuse"
}