Shader "IndianOcean/DarknessOverlay"
{
    // 黑暗遮罩 Shader v2 —— 乘法混合版（纯黑暗 + 光源，不含回声）
    // 回声描边已独立到 SpriteEchoOutline shader，由 EchoSystem 全局参数驱动。
    //
    // 乘法混合：finalColor = srcColor * dstColor
    // 黑暗区域：sceneColor * 0 = 纯黑（精灵完全看不见）
    // 光照区域：sceneColor * 1 = 原色（完全可见）
    Properties
    {
        _DarknessColor ("黑暗底色（夜间微光色调）", Color) = (0.01, 0.01, 0.02, 1)
        _MinBrightness ("最小亮度（0=纯黑不可见, 0.05=微光）", Range(0, 0.3)) = 0.0
        _LightSoftness ("光线柔和度（边缘渐变宽度）", Range(0.01, 1.0)) = 0.35
    }
    SubShader
    {
        Tags
        {
            "RenderType" = "Transparent"
            "Queue" = "Transparent+100"
            "RenderPipeline" = "UniversalPipeline"
        }
        Blend DstColor Zero
        ZWrite Off
        ZTest Always
        Cull Off

        Pass
        {
            Name "DarknessOverlay"
            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_instancing

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

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

            struct Varyings
            {
                float4 positionCS : SV_POSITION;
                float2 uv : TEXCOORD0;
                float3 worldPos : TEXCOORD1;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            CBUFFER_START(UnityPerMaterial)
                float4 _DarknessColor;
                float  _MinBrightness;
                float  _LightSoftness;
            CBUFFER_END

            // 光源数据数组：xy = 世界坐标 XZ, z = 半径, w = 强度(0~1)
            float4 _LightData[64];
            int    _LightCount;

            Varyings vert(Attributes input)
            {
                Varyings output;
                UNITY_SETUP_INSTANCE_ID(input);
                UNITY_TRANSFER_INSTANCE_ID(input, output);

                output.positionCS = TransformObjectToHClip(input.positionOS.xyz);
                output.uv = input.uv;
                output.worldPos = TransformObjectToWorld(input.positionOS.xyz);
                return output;
            }

            half4 frag(Varyings input) : SV_Target
            {
                // 2.5D 俯视角：用世界坐标的 XZ 平面计算距离
                float2 worldPos = input.worldPos.xz;
                float lightAmount = 0.0;

                // 常规光源
                for (int i = 0; i < _LightCount; i++)
                {
                    float2 lightPos = _LightData[i].xy;
                    float  radius   = _LightData[i].z;
                    float  intensity= _LightData[i].w;

                    float dist = distance(worldPos, lightPos);
                    float innerRadius = radius * (1.0 - _LightSoftness);
                    float light = 1.0 - smoothstep(innerRadius, radius, dist);
                    light *= intensity;
                    lightAmount = max(lightAmount, light);
                }

                // 最小亮度：全黑区域是否允许微微看到东西
                lightAmount = max(lightAmount, _MinBrightness);

                // 从黑暗底色插值到白色
                float3 maskColor = lerp(_DarknessColor.rgb, float3(1.0, 1.0, 1.0), lightAmount);
                return half4(maskColor, 1.0);
            }
            ENDHLSL
        }
    }
    FallBack Off
}