Shader "Bansonic/Sprite Vertical Glow Only"
{
    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) = (0.75,0.95,1,1)
        _Threshold ("Alpha Threshold", Range(0, 1)) = 0.08
        _Intensity ("Glow Intensity", Range(0, 12)) = 3
        _GlowRadius ("Edge Radius (Texels)", Range(0, 24)) = 4
        _ExpandX ("Horizontal Expand", Range(0, 1)) = 0.08
        _ExpandYBottom ("Bottom Expand", Range(0, 1)) = 0.03
        _ExpandYTop ("Top Expand", Range(0, 6)) = 2.2
        _VerticalStart ("Vertical Start", Range(0, 1)) = 0.1
        _BottomFade ("Bottom Fade", Range(0, 1)) = 0.15
        _CoreSuppress ("Core Suppress", Range(0, 1)) = 0.75
        _SidePower ("Side Power", Range(0.5, 6)) = 1.8
        _TopPower ("Top Power", Range(0.5, 6)) = 2.0
    }

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

        Cull Off
        ZWrite Off
        Blend One One

        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 vert
            #pragma fragment frag
            #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;
                half _ExpandX;
                half _ExpandYBottom;
                half _ExpandYTop;
                half _VerticalStart;
                half _BottomFade;
                half _CoreSuppress;
                half _SidePower;
                half _TopPower;
            CBUFFER_END

            Varyings vert(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);

                float2 uv = input.uv;
                float2 sign2 = float2(uv.x < 0.5 ? -1.0 : 1.0, uv.y < 0.5 ? -1.0 : 1.0);
                float yExpand = lerp((float)_ExpandYBottom, (float)_ExpandYTop, uv.y);
                input.positionOS.xy += float2(sign2.x * _ExpandX, sign2.y * yExpand);

                output.positionCS = TransformObjectToHClip(input.positionOS);
                output.uv = uv;
                output.color = input.color * _Color * unity_SpriteColor;
                return output;
            }

            float SampleAlpha(float2 uv, half4 tint)
            {
                half4 c = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, uv) * tint;
                return saturate((c.a - _Threshold) / max(1e-4, 1.0 - _Threshold));
            }

            float EdgeField(float2 uv, half4 tint)
            {
                float2 texel = _MainTex_TexelSize.xy * max((float)_GlowRadius, 0.0001);
                float c = SampleAlpha(uv, tint);
                float n = SampleAlpha(uv + texel * float2(0, 1), tint);
                float s = SampleAlpha(uv + texel * float2(0, -1), tint);
                float e = SampleAlpha(uv + texel * float2(1, 0), tint);
                float w = SampleAlpha(uv + texel * float2(-1, 0), tint);
                float ne = SampleAlpha(uv + texel * float2(1, 1), tint);
                float nw = SampleAlpha(uv + texel * float2(-1, 1), tint);
                float se = SampleAlpha(uv + texel * float2(1, -1), tint);
                float sw = SampleAlpha(uv + texel * float2(-1, -1), tint);

                float dilated = max(max(max(n, s), max(e, w)), max(max(ne, nw), max(se, sw)));
                return saturate(dilated - c);
            }

            half4 frag(Varyings input) : SV_Target
            {
                half4 tint = input.color;
                float a = SampleAlpha(input.uv, tint);
                float edge = EdgeField(input.uv, tint);

                float side = smoothstep(0.30, 0.50, abs(input.uv.x - 0.5) * 2.0);
                float vertical = smoothstep(_VerticalStart, 1.0, input.uv.y);
                float top = pow(saturate(input.uv.y), _TopPower);
                float bottomFade = lerp(1.0, _BottomFade, saturate(1.0 - input.uv.y));

                float glowMask = max(edge * 2.5, side * vertical * top);
                glowMask *= bottomFade;
                glowMask *= (1.0 - a * _CoreSuppress);

                half alpha = saturate(glowMask * _Intensity);
                half3 rgb = _GlowColor.rgb * alpha * _GlowColor.a;
                return half4(rgb, alpha);
            }
            ENDHLSL
        }
    }
}