Shader "Custom/OutLineShader"
{
    Properties
    {
        _MainTex("Base (RGB)", 2D) = "white" {}
        _OutlineColor("Outline Color", Color) = (.0, .0, .0, .0)
        _OutlineWidth("Outline Width", Range(0, 10)) = .0
        _MaskTex("Mask Texture", 2D) = "white" {}
    }
        SubShader
    {
        Tags { "RenderType" = "Overlay" }
        Pass
        {
            Name "OUTLINE"
            ZWrite Off
            ZTest Always
            Blend SrcAlpha OneMinusSrcAlpha
            ColorMask RGB
            Stencil
            {
                Ref 1
                Comp Always
                Pass Replace
            }

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

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

            struct v2f
            {
                float4 pos : POSITION;
            };

            float _OutlineWidth;
            float4 _OutlineColor;
            sampler2D _MaskTex;

            v2f vert(appdata v)
            {
                v2f o;
                float2 offset = float2(_OutlineWidth / _ScreenParams.x, _OutlineWidth / _ScreenParams.y);
                o.pos = UnityObjectToClipPos(v.vertex) + float4(offset, 0, 0) * v.vertex.w;
                return o;
            }

            half4 frag(v2f i) : COLOR
            {
                // Apply mask texture to control where the outline is visible
                float mask = tex2D(_MaskTex, i.pos.xy / i.pos.w).r;
                return _OutlineColor * mask;
            }
            ENDCG
        }
        Pass
        {
            Name "BASE"
            ZWrite Off
            ZTest Always
            Blend SrcAlpha OneMinusSrcAlpha
            ColorMask RGB
            Stencil
            {
                Ref 1
                Comp Equal
                Pass Keep
            }

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

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

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

            sampler2D _MainTex;

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

            half4 frag(v2f i) : COLOR
            {
                return tex2D(_MainTex, i.uv);
            }
            ENDCG
        }
    }
}