Shader "Custom/Outlight"
{
    Properties
    {
        _MainTex("Texture", 2D) = "white" {}
        _LightColor("Light Color", Color) = (1.0, 1.0, 1.0, 1.0)
        _Size("Size", Float) = 1
    }

        SubShader{

            Blend SrcAlpha OneMinusSrcAlpha

            CGINCLUDE
            #include "UnityCG.cginc"

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

            sampler2D _MainTex;
            float4 _MainTex_ST;
            half4 _MainTex_TexelSize;
            float4 _LightColor;
            float _Size;

            ENDCG

            Pass {

                CGPROGRAM
                #pragma vertex vert
                #pragma fragment frag
                #include "UnityCG.cginc"

                v2f vert(appdata_img IN)
                {
                    v2f OUT;
                    OUT.pos = UnityObjectToClipPos(IN.vertex);
                    OUT.uv = TRANSFORM_TEX(IN.texcoord, _MainTex);
                    return OUT;
                }

                fixed4 frag(v2f IN) : SV_Target
                {
                    fixed4 color = tex2D(_MainTex, IN.uv);
                    fixed4 c = _LightColor;
                    float sum = tex2D(_MainTex, IN.uv).a;
                    for (float i = 1.0; i <= _Size; i += 1.0) {
                        sum += tex2D(_MainTex, IN.uv + _MainTex_TexelSize.xy * half2(i, 0)).a;
                        sum += tex2D(_MainTex, IN.uv + _MainTex_TexelSize.xy * half2(-1.0 * i, 0)).a;
                        sum += tex2D(_MainTex, IN.uv + _MainTex_TexelSize.xy * half2(0, 1.0 * i)).a;
                        sum += tex2D(_MainTex, IN.uv + _MainTex_TexelSize.xy * half2(0, -1.0 * i)).a;
                    }

                    c.a = sum / (4.0 * _Size + 1.0);

                    return step(0.1, color.a) * color + step(0.1, 1.0 - color.a) * c;
                }

                ENDCG
            }
        }
}