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

        _ShadowColor ("Shadow Color", Color) = (0,0,0,0.5)
        _ShadowOffset ("Shadow Offset (XY)", Vector) = (4, -4, 0, 0)
        _ShadowSkew ("Shadow Skew (XY)", Vector) = (0, 0, 0, 0)
        _ShadowSoftness ("Shadow Softness", Range(0, 1)) = 0.1
        _ShadowBlur ("Shadow Blur Range", Range(0, 50)) = 0
        _ShadowBlurIntensity ("Shadow Blur Intensity", 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

        [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

            #pragma multi_compile_local _ UNITY_UI_CLIP_RECT
            #pragma multi_compile_local _ UNITY_UI_ALPHACLIP
            #pragma multi_compile_instancing

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

            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;
                float2 shadowUV : TEXCOORD2;
                UNITY_VERTEX_OUTPUT_STEREO
            };

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

            fixed4 _ShadowColor;
            float4 _ShadowOffset;
            float4 _ShadowSkew;
            float _ShadowSoftness;
            float _ShadowBlur;
            float _ShadowBlurIntensity;
            float4 _MainTex_TexelSize;

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

                OUT.worldPosition = v.vertex;
                OUT.vertex = UnityObjectToClipPos(v.vertex);
                OUT.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
                OUT.color = v.color * _Color;

                float2 shadowUV = v.texcoord;

                float2 centeredUV = v.texcoord - 0.5;
                shadowUV.x += centeredUV.y * _ShadowSkew.x;
                shadowUV.y += centeredUV.x * _ShadowSkew.y;

                shadowUV += _ShadowOffset.xy * 0.01;

                OUT.shadowUV = shadowUV;

                return OUT;
            }

            fixed4 frag(v2f IN) : SV_Target
            {
                fixed4 color = (tex2D(_MainTex, IN.texcoord) + _TextureSampleAdd) * IN.color;

                fixed sharpAlpha = (tex2D(_MainTex, IN.shadowUV) + _TextureSampleAdd).a;

                float2 blurStep = _MainTex_TexelSize.xy * _ShadowBlur;
                fixed blurredAlpha = 0;
                blurredAlpha = max(blurredAlpha, (tex2D(_MainTex, IN.shadowUV + float2(-blurStep.x, -blurStep.y)) + _TextureSampleAdd).a);
                blurredAlpha = max(blurredAlpha, (tex2D(_MainTex, IN.shadowUV + float2(       0.0, -blurStep.y)) + _TextureSampleAdd).a);
                blurredAlpha = max(blurredAlpha, (tex2D(_MainTex, IN.shadowUV + float2( blurStep.x, -blurStep.y)) + _TextureSampleAdd).a);
                blurredAlpha = max(blurredAlpha, (tex2D(_MainTex, IN.shadowUV + float2(-blurStep.x,        0.0)) + _TextureSampleAdd).a);
                blurredAlpha = max(blurredAlpha, (tex2D(_MainTex, IN.shadowUV                                  ) + _TextureSampleAdd).a);
                blurredAlpha = max(blurredAlpha, (tex2D(_MainTex, IN.shadowUV + float2( blurStep.x,        0.0)) + _TextureSampleAdd).a);
                blurredAlpha = max(blurredAlpha, (tex2D(_MainTex, IN.shadowUV + float2(-blurStep.x,  blurStep.y)) + _TextureSampleAdd).a);
                blurredAlpha = max(blurredAlpha, (tex2D(_MainTex, IN.shadowUV + float2(       0.0,  blurStep.y)) + _TextureSampleAdd).a);
                blurredAlpha = max(blurredAlpha, (tex2D(_MainTex, IN.shadowUV + float2( blurStep.x,  blurStep.y)) + _TextureSampleAdd).a);

                fixed shadowAlpha = lerp(sharpAlpha, blurredAlpha, _ShadowBlurIntensity) * _ShadowColor.a;

                fixed4 result;
                result.rgb = lerp(_ShadowColor.rgb * shadowAlpha, color.rgb, color.a);
                result.a = saturate(shadowAlpha * (1.0 - color.a) + color.a);

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

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

                return result;
            }
            ENDCG
        }
    }
}