Shader "LeEthER/GradientFlowEmission"
{
    Properties
    {
        [MainTexture] _BaseMap("Base Map", 2D) = "white" {}
        [MainColor] _BaseColor("Base Color", Color) = (1,1,1,1)

        _EmissionMask("Emission Mask", 2D) = "white" {}
        [HDR] _EmissionColorA("Emission Color A", Color) = (0, 0.8, 1, 1)
        [HDR] _EmissionColorB("Emission Color B", Color) = (1, 0.2, 0.8, 1)
        _EmissionIntensity("Emission Intensity", Range(0, 10)) = 1.5

        _FlowDirection("Flow Direction", Vector) = (1, 0, 0, 0)
        _FlowSpeed("Flow Speed", Range(-5, 5)) = 1
        _FlowScale("Flow Scale", Range(0.1, 20)) = 3
        _FlowSharpness("Flow Sharpness", Range(0.1, 10)) = 2
        _FlowContrast("Flow Contrast", Range(0.1, 5)) = 1

        _EmissionPulse("Emission Pulse", Range(0, 1)) = 0.25
    }

    SubShader
    {
        Tags
        {
            "RenderType"="Opaque"
            "RenderPipeline"="UniversalPipeline"
            "Queue"="Geometry"
        }

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

            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

            struct Attributes
            {
                float4 positionOS : POSITION;
                float2 uv         : TEXCOORD0;
            };

            struct Varyings
            {
                float4 positionHCS : SV_POSITION;
                float2 uv          : TEXCOORD0;
            };

            TEXTURE2D(_BaseMap);
            SAMPLER(sampler_BaseMap);

            TEXTURE2D(_EmissionMask);
            SAMPLER(sampler_EmissionMask);

            CBUFFER_START(UnityPerMaterial)
                float4 _BaseMap_ST;
                float4 _EmissionMask_ST;
                float4 _BaseColor;
                float4 _EmissionColorA;
                float4 _EmissionColorB;
                float4 _FlowDirection;
                float _EmissionIntensity;
                float _FlowSpeed;
                float _FlowScale;
                float _FlowSharpness;
                float _FlowContrast;
                float _EmissionPulse;
            CBUFFER_END

            Varyings vert(Attributes IN)
            {
                Varyings OUT;
                OUT.positionHCS = TransformObjectToHClip(IN.positionOS.xyz);
                OUT.uv = TRANSFORM_TEX(IN.uv, _BaseMap);
                return OUT;
            }

            half4 frag(Varyings IN) : SV_Target
            {
                float2 uv = IN.uv;

                half4 baseCol = SAMPLE_TEXTURE2D(_BaseMap, sampler_BaseMap, uv) * _BaseColor;
                half emissionMask = SAMPLE_TEXTURE2D(_EmissionMask, sampler_EmissionMask, uv).r;

                float2 dir = _FlowDirection.xy;
                dir = length(dir) > 0.0001 ? normalize(dir) : float2(1, 0);

                // 방향을 따라 흐르는 값
                float flowCoord = dot(uv, dir) * _FlowScale + _Time.y * _FlowSpeed;

                // 0~1 반복되는 부드러운 웨이브
                float wave = sin(flowCoord * 6.2831853) * 0.5 + 0.5;

                // 명암 대비 조절
                wave = pow(saturate(wave), _FlowSharpness);
                wave = saturate((wave - 0.5) * _FlowContrast + 0.5);

                // 추가로 밝기 맥동
                float pulse = lerp(1.0, wave, _EmissionPulse);

                // A -> B 그라데이션
                half3 emissionGradient = lerp(_EmissionColorA.rgb, _EmissionColorB.rgb, wave);

                half3 emission = emissionGradient * emissionMask * _EmissionIntensity * pulse;

                return half4(baseCol.rgb + emission, baseCol.a);
            }
            ENDHLSL
        }
    }
}