Shader "Skybox/Cubemap Blend"
{
    Properties
    {
        [NoScaleOffset] _Cubemap1 ("Cubemap 1", CUBE) = "" {}
        [NoScaleOffset] _Cubemap2 ("Cubemap 2", CUBE) = "" {}
        [NoScaleOffset] _Cubemap3 ("Cubemap 3", CUBE) = "" {}
        _Blend ("Blend", Range(0, 1)) = 0
        _Tint ("Tint Color", Color) = (1, 1, 1, 1)
        _Exposure ("Exposure", Range(0, 8)) = 1.0
        _Rotation ("Rotation", Range(0, 360)) = 0
    }

    SubShader
    {
        Tags { "Queue"="Background" "RenderType"="Background" "PreviewType"="Skybox" }
        Cull Off
        ZWrite Off

        Pass
        {
            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag

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

            TEXTURECUBE(_Cubemap1);
            SAMPLER(sampler_Cubemap1);
            TEXTURECUBE(_Cubemap2);
            SAMPLER(sampler_Cubemap2);
            TEXTURECUBE(_Cubemap3);
            SAMPLER(sampler_Cubemap3);

            CBUFFER_START(UnityPerMaterial)
                half _Blend;
                half4 _Tint;
                half _Exposure;
                float _Rotation;
            CBUFFER_END

            struct Attributes
            {
                float4 positionOS : POSITION;
            };

            struct Varyings
            {
                float4 positionCS : SV_POSITION;
                float3 texcoord   : TEXCOORD0;
            };

            float3 RotateAroundYInDegrees(float3 dir, float degrees)
            {
                float rad = degrees * PI / 180.0;
                float s, c;
                sincos(rad, s, c);
                return float3(
                    dir.x * c - dir.z * s,
                    dir.y,
                    dir.x * s + dir.z * c
                );
            }

            Varyings vert(Attributes input)
            {
                Varyings output;
                float3 rotated = RotateAroundYInDegrees(input.positionOS.xyz, _Rotation);
                output.positionCS = TransformObjectToHClip(input.positionOS.xyz);
                output.texcoord = rotated;
                return output;
            }

            half4 frag(Varyings input) : SV_Target
            {
                half4 col1 = SAMPLE_TEXTURECUBE(_Cubemap1, sampler_Cubemap1, input.texcoord);
                half4 col2 = SAMPLE_TEXTURECUBE(_Cubemap2, sampler_Cubemap2, input.texcoord);
                half4 col3 = SAMPLE_TEXTURECUBE(_Cubemap3, sampler_Cubemap3, input.texcoord);

                // Blend 0~0.5: Cubemap1 → Cubemap2
                // Blend 0.5~1: Cubemap2 → Cubemap3
                half4 col;
                if (_Blend < 0.5)
                    col = lerp(col1, col2, _Blend * 2.0);
                else
                    col = lerp(col2, col3, (_Blend - 0.5) * 2.0);

                col.rgb *= _Tint.rgb * _Exposure;
                return col;
            }
            ENDHLSL
        }
    }

    Fallback Off
}