Shader "Sukuna/DistortionTrail"
{
    Properties
    {
        _DistortionStrength("Distortion Strength", Range(0, 1)) = 0.5
        _DistortionMap("Distortion Map", 2D) = "bump" {}
        _WidthMask("Width Mask", Range(0, 1)) = 0.5
    }

    SubShader
    {
        Tags { "RenderType"="Transparent" "Queue"="Transparent" "RenderPipeline" = "UniversalPipeline" }
        LOD 100

        Pass
        {
            ZWrite Off
            Blend SrcAlpha OneMinusSrcAlpha

            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/DeclareOpaqueTexture.hlsl"

            struct Attributes
            {
                float4 positionOS : POSITION;
                float2 uv : TEXCOORD0;
                float4 color : COLOR; // Sử dụng để lấy Alpha từ Trail Renderer
            };

            struct Varyings
            {
                float4 positionCS : SV_POSITION;
                float2 uv : TEXCOORD0;
                float4 screenPos : TEXCOORD1;
                float4 color : COLOR;
            };

            float _DistortionStrength;
            sampler2D _DistortionMap;
            float _WidthMask;

            Varyings vert(Attributes input)
            {
                Varyings output;
                output.positionCS = TransformObjectToHClip(input.positionOS.xyz);
                output.uv = input.uv;
                output.screenPos = ComputeScreenPos(output.positionCS);
                output.color = input.color;
                return output;
            }

            half4 frag(Varyings input) : SV_Target
            {
                // Mask cho trail: mờ ở 2 cạnh và mờ dần theo chiều dài
                float mask = (1.0 - abs(input.uv.y - 0.5) * 2.0) * input.uv.x * input.color.a;
                
                float2 noise = tex2D(_DistortionMap, input.uv * 2.0 + _Time.y).rg * 2.0 - 1.0;
                float2 screenUV = input.screenPos.xy / input.screenPos.w;
                float2 distortedUV = screenUV + noise * _DistortionStrength * 0.1 * mask;
                
                float3 background = SampleSceneColor(distortedUV);
                return float4(background, mask);
            }
            ENDHLSL
        }
    }
}