Shader "UI/UIGaussianBlur"
{
    Properties
    {
        [PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
        _Color ("Tint", Color) = (1,1,1,1)
        _BlurRadius ("Blur Radius (Pixels)", Range(0, 64)) = 2

        _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

        [HideInInspector] _TextureSampleAdd ("Texture Sample Add", Color) = (0,0,0,0)
        [HideInInspector] _MainTex_ST ("MainTex ST", Vector) = (1,1,0,0)
    }

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

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

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

        Pass
        {
            Name "Default"
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma target 3.0

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

            #pragma multi_compile_local _ UNITY_UI_CLIP_RECT
            #pragma multi_compile_local _ UNITY_UI_ALPHACLIP

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

            struct v2f
            {
                float4 vertex : SV_POSITION;
                fixed4 color : COLOR;
                float2 texcoord : TEXCOORD0;
                float4 worldPosition : TEXCOORD1;
                float4 mask : TEXCOORD2;
                UNITY_VERTEX_OUTPUT_STEREO
            };

            sampler2D _MainTex;
            fixed4 _Color;
            fixed4 _TextureSampleAdd;
            float4 _ClipRect;
            float4 _MainTex_ST;
            float4 _MainTex_TexelSize;
            float _UIMaskSoftnessX;
            float _UIMaskSoftnessY;
            float _BlurRadius;

            v2f vert(appdata_t v)
            {
                v2f o;
                UNITY_SETUP_INSTANCE_ID(v);
                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);

                float4 vPosition = UnityObjectToClipPos(v.vertex);
                o.worldPosition = v.vertex;
                o.vertex = vPosition;
                o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);

                float2 pixelSize = vPosition.w;
                pixelSize /= float2(1, 1) * abs(mul((float2x2)UNITY_MATRIX_P, _ScreenParams.xy));

                float4 clampedRect = clamp(_ClipRect, -2e10, 2e10);
                o.mask = float4(
                    v.vertex.xy * 2 - clampedRect.xy - clampedRect.zw,
                    0.25 / (0.25 * half2(_UIMaskSoftnessX, _UIMaskSoftnessY) + abs(pixelSize.xy))
                );

                o.color = v.color * _Color;
                return o;
            }

            fixed4 SampleBlur(float2 uv)
            {
                float blur = max(_BlurRadius, 0.0);
                if (blur <= 0.0001)
                {
                    return tex2D(_MainTex, uv);
                }

                float2 texel = _MainTex_TexelSize.xy * blur;
                const int sampleCount = 32;
                const float goldenAngle = 2.39996323;

                fixed4 c = tex2D(_MainTex, uv);
                float weightSum = 1.0;

                [unroll]
                for (int i = 0; i < sampleCount; i++)
                {
                    float fi = (float)i + 0.5;
                    float r = sqrt(fi / (float)sampleCount);
                    float a = fi * goldenAngle;
                    float2 dir = float2(cos(a), sin(a));
                    float2 offset = dir * r * texel;
                    float w = exp(-r * r * 3.5);
                    c += tex2D(_MainTex, uv + offset) * w;
                    weightSum += w;
                }

                return c / max(weightSum, 0.0001);
            }

            fixed4 frag(v2f IN) : SV_Target
            {
                const half alphaPrecision = half(0xff);
                const half invAlphaPrecision = half(1.0 / alphaPrecision);
                IN.color.a = round(IN.color.a * alphaPrecision) * invAlphaPrecision;

                float4 tex = SampleBlur(IN.texcoord.xy);
                tex += _TextureSampleAdd;

                fixed4 color = tex * IN.color;

                #ifdef UNITY_UI_CLIP_RECT
                half2 m = saturate((_ClipRect.zw - _ClipRect.xy - abs(IN.mask.xy)) * IN.mask.zw);
                color.a *= m.x * m.y;
                #endif

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

                color.rgb *= color.a;
                return color;
            }
            ENDCG
        }
    }
}