Shader "UI/EyeViewportOverlay"
{
    Properties
    {
        [PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
        _Color ("Tint", Color) = (0, 0, 0, 1)

        [Header(Eye Opening)]
        _EyeWidth ("Eye Width", Range(0.22, 0.58)) = 0.46
        _EyeHeight ("Eye Height", Range(0.15, 0.72)) = 0.28
        _EdgeSoftness ("Edge Softness", Range(0.001, 0.2)) = 0.022
        _BlinkOpen ("Blink Open", Range(0, 1)) = 1

        _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
    }

    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
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma target 2.0
            #include "UnityCG.cginc"
            #include "UnityUI.cginc"

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

            struct v2f
            {
                float4 vertex : SV_POSITION;
                fixed4 color : COLOR;
                float2 uv : TEXCOORD0;
                float4 worldPosition : TEXCOORD1;
                float4 screenPosition : TEXCOORD2;
            };

            sampler2D _MainTex;
            fixed4 _Color;
            float4 _ClipRect;

            float _EyeWidth;
            float _EyeHeight;
            float _EdgeSoftness;
            float _BlinkOpen;

            v2f vert(appdata v)
            {
                v2f o;
                o.worldPosition = v.vertex;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv;
                o.screenPosition = ComputeScreenPos(o.vertex);
                o.color = v.color * _Color;
                return o;
            }

            float FeatherBoundaryAlpha(float insideHard, float edgeDist, float softness)
            {
                float outside = 1.0 - insideHard;
                float edgeFeather = (1.0 - smoothstep(0.0, softness, edgeDist)) * insideHard;
                return saturate(outside + edgeFeather);
            }

            float ComputeViewportAlpha(float2 uv)
            {
                float2 c = uv - 0.5;
                float softness = max(0.001, _EdgeSoftness);
                float blinkOpen = saturate(_BlinkOpen);

                if (blinkOpen <= 0.001)
                {
                    return 1.0;
                }

                float rx = max(_EyeWidth, 0.001);
                float ry = max(_EyeHeight * blinkOpen, 0.001);

                float ellipseDist = length(float2(c.x / rx, c.y / ry));
                float insideHard = 1.0 - step(1.0, ellipseDist);
                float edgeDist = (1.0 - ellipseDist) * insideHard;
                return FeatherBoundaryAlpha(insideHard, edgeDist, softness);
            }

            fixed4 frag(v2f i) : SV_Target
            {
                float2 screenUv = i.screenPosition.xy / max(i.screenPosition.w, 0.0001);
                float alpha = ComputeViewportAlpha(saturate(screenUv));
                fixed4 col = fixed4(i.color.rgb, i.color.a * alpha);
                col.a *= UnityGet2DClipping(i.worldPosition.xy, _ClipRect);
                return col;
            }
            ENDCG
        }
    }

    Fallback Off
}