Shader "Bansonic/Sprite Glow"
{
    Properties
    {
        [PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
        [HideInInspector] _Color ("Tint", Color) = (1,1,1,1)
        [HideInInspector] PixelSnap ("Pixel snap", Float) = 0
        [HideInInspector] _RendererColor ("RendererColor", Color) = (1,1,1,1)
        [HideInInspector] _AlphaTex ("External Alpha", 2D) = "white" {}
        [HideInInspector] _EnableExternalAlpha ("Enable External Alpha", Float) = 0

        [HDR]_GlowColor ("Glow Color", Color) = (1,1,1,1)
        _Threshold ("Glow Threshold", Range(0, 4)) = 0.9
        _Intensity ("Glow Intensity", Range(0, 8)) = 1.5
        _GlowRadius ("Glow Radius", Range(0, 32)) = 6
    }

    SubShader
    {
        Tags
        {
            "Queue" = "Transparent"
            "RenderType" = "Transparent"
            "RenderPipeline" = "UniversalPipeline"
            "CanUseSpriteAtlas" = "True"
        }

        Blend SrcAlpha OneMinusSrcAlpha, One OneMinusSrcAlpha
        Cull Off
        ZWrite Off

        Pass
        {
            Tags { "LightMode" = "Universal2D" }

            HLSLPROGRAM
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
            #include "Packages/com.unity.render-pipelines.universal/Shaders/2D/Include/Core2D.hlsl"

            #pragma vertex SpriteVertex
            #pragma fragment SpriteFragment
            #pragma target 2.0
            #pragma multi_compile_instancing
            #pragma multi_compile _ SKINNED_SPRITE

            struct Attributes
            {
                float3 positionOS : POSITION;
                float4 color : COLOR;
                float2 uv : TEXCOORD0;
                UNITY_SKINNED_VERTEX_INPUTS
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct Varyings
            {
                float4 positionCS : SV_POSITION;
                half4 color : COLOR;
                float2 uv : TEXCOORD0;
                UNITY_VERTEX_OUTPUT_STEREO
            };

            TEXTURE2D(_MainTex);
            SAMPLER(sampler_MainTex);
            float4 _MainTex_TexelSize;

            CBUFFER_START(UnityPerMaterial)
                half4 _Color;
                half4 _GlowColor;
                half _Threshold;
                half _Intensity;
                half _GlowRadius;
            CBUFFER_END

            Varyings SpriteVertex(Attributes input)
            {
                Varyings output = (Varyings)0;
                UNITY_SETUP_INSTANCE_ID(input);
                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(output);
                UNITY_SKINNED_VERTEX_COMPUTE(input);

                SetUpSpriteInstanceProperties();
                input.positionOS = UnityFlipSprite(input.positionOS, unity_SpriteProps.xy);
                output.positionCS = TransformObjectToHClip(input.positionOS);
                output.uv = input.uv;
                output.color = input.color * _Color * unity_SpriteColor;
                return output;
            }

            half GetLuminance(half3 color)
            {
                return dot(color, half3(0.2126h, 0.7152h, 0.0722h));
            }

            half SampleGlowMask(float2 uv, half4 tint)
            {
                half4 tex = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, uv) * tint;
                half luminance = GetLuminance(tex.rgb);
                half mask = smoothstep(_Threshold - 0.18h, _Threshold + 0.18h, luminance);
                return mask * tex.a;
            }

            half ComputeGlow(float2 uv, half4 tint)
            {
                float2 texel = _MainTex_TexelSize.xy * max(_GlowRadius, 0.001h) * 1.5;

                const half w0 = 0.180h;
                const half w1 = 0.150h;
                const half w2 = 0.120h;
                const half w3 = 0.090h;
                const half w4 = 0.060h;

                half sum = SampleGlowMask(uv, tint) * w0;

                sum += SampleGlowMask(uv + texel * float2( 0.65,  0.00), tint) * w1;
                sum += SampleGlowMask(uv + texel * float2(-0.65,  0.00), tint) * w1;
                sum += SampleGlowMask(uv + texel * float2( 0.00,  0.65), tint) * w1;
                sum += SampleGlowMask(uv + texel * float2( 0.00, -0.65), tint) * w1;

                sum += SampleGlowMask(uv + texel * float2( 0.50,  0.50), tint) * w2;
                sum += SampleGlowMask(uv + texel * float2(-0.50,  0.50), tint) * w2;
                sum += SampleGlowMask(uv + texel * float2( 0.50, -0.50), tint) * w2;
                sum += SampleGlowMask(uv + texel * float2(-0.50, -0.50), tint) * w2;

                sum += SampleGlowMask(uv + texel * float2( 1.35,  0.00), tint) * w3;
                sum += SampleGlowMask(uv + texel * float2(-1.35,  0.00), tint) * w3;
                sum += SampleGlowMask(uv + texel * float2( 0.00,  1.35), tint) * w3;
                sum += SampleGlowMask(uv + texel * float2( 0.00, -1.35), tint) * w3;

                sum += SampleGlowMask(uv + texel * float2( 1.00,  1.00), tint) * w4;
                sum += SampleGlowMask(uv + texel * float2(-1.00,  1.00), tint) * w4;
                sum += SampleGlowMask(uv + texel * float2( 1.00, -1.00), tint) * w4;
                sum += SampleGlowMask(uv + texel * float2(-1.00, -1.00), tint) * w4;

                return sum;
            }

            half4 SpriteFragment(Varyings input) : SV_Target
            {
                half4 baseSample = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, input.uv) * input.color;
                half glowStrength = ComputeGlow(input.uv, input.color) * _Intensity * 1.75h;
                half3 glow = _GlowColor.rgb * glowStrength * _GlowColor.a;

                half4 color = baseSample;
                color.rgb += glow;
                color.a = saturate(baseSample.a + glowStrength * 0.55h);
                return color;
            }
            ENDHLSL
        }

        Pass
        {
            Tags { "LightMode" = "UniversalForward" }

            HLSLPROGRAM
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
            #include "Packages/com.unity.render-pipelines.universal/Shaders/2D/Include/Core2D.hlsl"

            #pragma vertex SpriteVertex
            #pragma fragment SpriteFragment
            #pragma target 2.0
            #pragma multi_compile_instancing
            #pragma multi_compile _ SKINNED_SPRITE

            struct Attributes
            {
                float3 positionOS : POSITION;
                float4 color : COLOR;
                float2 uv : TEXCOORD0;
                UNITY_SKINNED_VERTEX_INPUTS
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct Varyings
            {
                float4 positionCS : SV_POSITION;
                half4 color : COLOR;
                float2 uv : TEXCOORD0;
                UNITY_VERTEX_OUTPUT_STEREO
            };

            TEXTURE2D(_MainTex);
            SAMPLER(sampler_MainTex);
            float4 _MainTex_TexelSize;

            CBUFFER_START(UnityPerMaterial)
                half4 _Color;
                half4 _GlowColor;
                half _Threshold;
                half _Intensity;
                half _GlowRadius;
            CBUFFER_END

            Varyings SpriteVertex(Attributes input)
            {
                Varyings output = (Varyings)0;
                UNITY_SETUP_INSTANCE_ID(input);
                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(output);
                UNITY_SKINNED_VERTEX_COMPUTE(input);

                SetUpSpriteInstanceProperties();
                input.positionOS = UnityFlipSprite(input.positionOS, unity_SpriteProps.xy);
                output.positionCS = TransformObjectToHClip(input.positionOS);
                output.uv = input.uv;
                output.color = input.color * _Color * unity_SpriteColor;
                return output;
            }

            half GetLuminance(half3 color)
            {
                return dot(color, half3(0.2126h, 0.7152h, 0.0722h));
            }

            half SampleGlowMask(float2 uv, half4 tint)
            {
                half4 tex = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, uv) * tint;
                half luminance = GetLuminance(tex.rgb);
                half mask = smoothstep(_Threshold - 0.18h, _Threshold + 0.18h, luminance);
                return mask * tex.a;
            }

            half ComputeGlow(float2 uv, half4 tint)
            {
                float2 texel = _MainTex_TexelSize.xy * max(_GlowRadius, 0.001h) * 1.5;

                const half w0 = 0.180h;
                const half w1 = 0.150h;
                const half w2 = 0.120h;
                const half w3 = 0.090h;
                const half w4 = 0.060h;

                half sum = SampleGlowMask(uv, tint) * w0;

                sum += SampleGlowMask(uv + texel * float2( 0.65,  0.00), tint) * w1;
                sum += SampleGlowMask(uv + texel * float2(-0.65,  0.00), tint) * w1;
                sum += SampleGlowMask(uv + texel * float2( 0.00,  0.65), tint) * w1;
                sum += SampleGlowMask(uv + texel * float2( 0.00, -0.65), tint) * w1;

                sum += SampleGlowMask(uv + texel * float2( 0.50,  0.50), tint) * w2;
                sum += SampleGlowMask(uv + texel * float2(-0.50,  0.50), tint) * w2;
                sum += SampleGlowMask(uv + texel * float2( 0.50, -0.50), tint) * w2;
                sum += SampleGlowMask(uv + texel * float2(-0.50, -0.50), tint) * w2;

                sum += SampleGlowMask(uv + texel * float2( 1.35,  0.00), tint) * w3;
                sum += SampleGlowMask(uv + texel * float2(-1.35,  0.00), tint) * w3;
                sum += SampleGlowMask(uv + texel * float2( 0.00,  1.35), tint) * w3;
                sum += SampleGlowMask(uv + texel * float2( 0.00, -1.35), tint) * w3;

                sum += SampleGlowMask(uv + texel * float2( 1.00,  1.00), tint) * w4;
                sum += SampleGlowMask(uv + texel * float2(-1.00,  1.00), tint) * w4;
                sum += SampleGlowMask(uv + texel * float2( 1.00, -1.00), tint) * w4;
                sum += SampleGlowMask(uv + texel * float2(-1.00, -1.00), tint) * w4;

                return sum;
            }

            half4 SpriteFragment(Varyings input) : SV_Target
            {
                half4 baseSample = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, input.uv) * input.color;
                half glowStrength = ComputeGlow(input.uv, input.color) * _Intensity * 1.75h;
                half3 glow = _GlowColor.rgb * glowStrength * _GlowColor.a;

                half4 color = baseSample;
                color.rgb += glow;
                color.a = saturate(baseSample.a + glowStrength * 0.55h);
                return color;
            }
            ENDHLSL
        }
    }

    FallBack "Universal Render Pipeline/2D/Sprite-Unlit-Default"
}