Shader "IndianOcean/PortalVortex"
{
    // 传送门旋涡 Shader
    // 顺时针旋转 + 中心扭曲 + 发光效果
    // 基于 URP 管线
    Properties
    {
        _MainTex ("主贴图", 2D) = "white" {}
        _RotationSpeed ("旋转速度", Range(-5.0, 5.0)) = 1.5
        _VortexStrength ("扭曲强度", Range(0.0, 3.0)) = 1.0
        _CenterGlow ("中心发光强度", Range(0.0, 3.0)) = 1.5
        _Color ("色调", Color) = (1.0, 1.0, 1.0, 1.0)
    }
    SubShader
    {
        Tags
        {
            "RenderType" = "Transparent"
            "Queue" = "Transparent"
            "RenderPipeline" = "UniversalPipeline"
        }

        Blend SrcAlpha OneMinusSrcAlpha
        ZWrite Off
        ZTest LEqual
        Cull Off

        Pass
        {
            Name "PortalVortex"
            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;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

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

            CBUFFER_START(UnityPerMaterial)
                float4 _MainTex_ST;
                float  _RotationSpeed;
                float  _VortexStrength;
                float  _CenterGlow;
                float4 _Color;
            CBUFFER_END

            TEXTURE2D(_MainTex);
            SAMPLER(sampler_MainTex);

            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 = TRANSFORM_TEX(input.uv, _MainTex);
                return output;
            }

            half4 frag(Varyings input) : SV_Target
            {
                // UV 中心点
                float2 center = float2(0.5, 0.5);
                float2 uvOffset = input.uv - center;

                // 极坐标：距离和角度
                float dist = length(uvOffset);
                float angle = atan2(uvOffset.y, uvOffset.x);

                // 顺时针旋转：角度减去时间 * 速度
                float rotation = _Time.y * _RotationSpeed;

                // 扭曲强度随距离减小（中心扭曲更大）
                float twist = _VortexStrength * (1.0 - dist * 2.0);
                twist = max(twist, 0.0);

                // 应用旋转 + 扭曲
                float finalAngle = angle - rotation - twist * 3.14159;

                // 转换回 UV 坐标
                float2 vortexUV = center + float2(
                    cos(finalAngle) * dist,
                    sin(finalAngle) * dist
                );

                // 采样主贴图
                half4 texColor = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, vortexUV);

                // 中心发光：距离中心越近越亮
                float glow = _CenterGlow * (1.0 - dist * 2.0);
                glow = max(glow, 0.0);

                // 边缘柔和过渡
                float edgeFade = 1.0 - smoothstep(0.35, 0.5, dist);

                // 最终颜色 = 贴图色 + 中心发光 * 蓝色调
                float3 glowColor = float3(0.2, 0.6, 1.0) * glow;
                float3 finalColor = texColor.rgb * _Color.rgb + glowColor;

                float alpha = texColor.a * edgeFade;

                return half4(finalColor, alpha);
            }
            ENDHLSL
        }
    }
    FallBack Off
}