Shader "BriarQueen/UI/Edge Darken"
{
    Properties
    {
        [PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
        _Color ("Tint", Color) = (0, 0, 0, 0.65)

        _Amount ("Amount", Range(0, 1)) = 1
        _EdgeDarkness ("Edge Darkness", Range(0, 1)) = 1
        _CenterDarkness ("Center Darkness", Range(0, 1)) = 0
        _EdgeWidth ("Edge Width", Range(0.001, 0.5)) = 0.22
        _Softness ("Softness", Range(0.001, 0.5)) = 0.18
        [HideInInspector] _RectSize ("Rect Size", Vector) = (1, 1, 0, 0)
        [HideInInspector] _RectPivot ("Rect Pivot", Vector) = (0.5, 0.5, 0, 0)

        _StencilComp ("Stencil Comparison", Float) = 8
        _Stencil ("Stencil ID", Float) = 0
        _StencilOp ("Stencil Operation", Float) = 0
        _StencilWriteMask ("Stencil Write Mask", Float) = 255
        _StencilReadMask ("Stencil Read Mask", Float) = 255
        _ColorMask ("Color Mask", Float) = 15

        [Toggle(UNITY_UI_ALPHACLIP)] _UseUIAlphaClip ("Use Alpha Clip", Float) = 0
    }

    SubShader
    {
        Tags
        {
            "Queue" = "Transparent"
            "IgnoreProjector" = "True"
            "RenderType" = "Transparent"
            "PreviewType" = "Plane"
            "CanUseSpriteAtlas" = "True"
        }

        Stencil
        {
            Ref [_Stencil]
            Comp [_StencilComp]
            Pass [_StencilOp]
            ReadMask [_StencilReadMask]
            WriteMask [_StencilWriteMask]
        }

        Cull Off
        Lighting Off
        ZWrite Off
        ZTest [unity_GUIZTestMode]
        Blend SrcAlpha OneMinusSrcAlpha
        ColorMask [_ColorMask]

        Pass
        {
            Name "Default"

            CGPROGRAM
            #pragma vertex Vert
            #pragma fragment Frag
            #pragma target 2.0

            #include "UnityCG.cginc"
            #include "UnityUI.cginc"

            #pragma multi_compile_local _ UNITY_UI_CLIP_RECT
            #pragma multi_compile_local _ UNITY_UI_ALPHACLIP

            struct AppData
            {
                float4 vertex : POSITION;
                float4 color : COLOR;
                float2 texcoord : TEXCOORD0;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct Varyings
            {
                float4 vertex : SV_POSITION;
                fixed4 color : COLOR;
                float2 uv : TEXCOORD0;
                float2 localPosition : TEXCOORD1;
                float4 worldPosition : TEXCOORD2;
                UNITY_VERTEX_OUTPUT_STEREO
            };

            sampler2D _MainTex;
            fixed4 _Color;
            fixed4 _TextureSampleAdd;
            float4 _ClipRect;

            float _Amount;
            float _EdgeDarkness;
            float _CenterDarkness;
            float _EdgeWidth;
            float _Softness;
            float4 _RectSize;
            float4 _RectPivot;

            Varyings Vert(AppData input)
            {
                Varyings output;

                UNITY_SETUP_INSTANCE_ID(input);
                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(output);

                output.worldPosition = input.vertex;
                output.vertex = UnityObjectToClipPos(input.vertex);
                output.uv = input.texcoord;
                output.localPosition = input.vertex.xy;
                output.color = input.color * _Color;

                return output;
            }

            fixed4 Frag(Varyings input) : SV_Target
            {
                fixed4 color = (tex2D(_MainTex, input.uv) + _TextureSampleAdd) * input.color;

                float2 safeRectSize = max(_RectSize.xy, float2(0.0001, 0.0001));
                float2 rectUv = saturate((input.localPosition / safeRectSize) + _RectPivot.xy);
                float edgeDistance = min(
                    min(rectUv.x, 1.0 - rectUv.x),
                    min(rectUv.y, 1.0 - rectUv.y));
                float outerEdge = 1.0 - smoothstep(_EdgeWidth, _EdgeWidth + _Softness, edgeDistance);
                float darkness = lerp(_CenterDarkness, _EdgeDarkness, outerEdge);

                color.a *= saturate(_Amount) * darkness;

                #ifdef UNITY_UI_CLIP_RECT
                color.a *= UnityGet2DClipping(input.worldPosition.xy, _ClipRect);
                #endif

                #ifdef UNITY_UI_ALPHACLIP
                clip(color.a - 0.001);
                #endif

                return color;
            }
            ENDCG
        }
    }
}