Shader "BriarQueen/UI/Light Glow"
{
    Properties
    {
        [PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
        _Color ("Tint", Color) = (1, 1, 1, 1)

        _LightColor ("Light Color", Color) = (1, 0.78, 0.35, 1)
        _Intensity ("Intensity", Range(0, 8)) = 1.5
        _Radius ("Radius", Range(0, 1)) = 0.35
        _Falloff ("Falloff", Range(0.001, 1)) = 0.35
        _Softness ("Softness", Range(0.25, 6)) = 1.6
        _Center ("Center", Vector) = (0.5, 0.5, 0, 0)

        _FlickerStrength ("Flicker Strength", Range(0, 1)) = 0.08
        _FlickerSpeed ("Flicker Speed", Range(0, 20)) = 6
        _FlickerOffset ("Flicker Offset", Float) = 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 One
        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;
                float4 worldPosition : TEXCOORD1;
                UNITY_VERTEX_OUTPUT_STEREO
            };

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

            fixed4 _LightColor;
            float _Intensity;
            float _Radius;
            float _Falloff;
            float _Softness;
            float4 _Center;
            float _FlickerStrength;
            float _FlickerSpeed;
            float _FlickerOffset;

            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.color = input.color * _Color;

                return output;
            }

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

                float dist = distance(input.uv, _Center.xy);
                float glow = 1.0 - smoothstep(_Radius, _Radius + _Falloff, dist);
                glow = pow(saturate(glow), _Softness);

                float flickerA = sin((_Time.y + _FlickerOffset) * _FlickerSpeed);
                float flickerB = sin((_Time.y + _FlickerOffset) * _FlickerSpeed * 2.37 + 1.91);
                float flicker = 1.0 + ((flickerA * 0.65 + flickerB * 0.35) * _FlickerStrength);

                float alpha = glow * sprite.a * input.color.a * _LightColor.a * saturate(flicker);

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

                fixed4 color;
                color.rgb = _LightColor.rgb * _Intensity;
                color.a = alpha;

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

                return color;
            }
            ENDCG
        }
    }
}