Shader "TrashMaze/BackgroundVisibility"
{
    Properties
    {
        _LitTex ("Lit Texture (Color)", 2D) = "white" {}
        _UnlitTex ("Unlit Texture (Dark)", 2D) = "white" {}
        _TransitionSoftness ("Transition Softness", Range(0, 2)) = 0.5
    }
    
    SubShader
    {
        Tags 
        { 
            "Queue"="Background" 
            "RenderType"="Opaque" 
        }
        
        LOD 100
        
        Pass
        {
            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
            {
                float2 uv : TEXCOORD0;
                float3 positionWS : TEXCOORD1;
                float4 positionCS : SV_POSITION;
            };
            
            TEXTURE2D(_LitTex);
            SAMPLER(sampler_LitTex);
            TEXTURE2D(_UnlitTex);
            SAMPLER(sampler_UnlitTex);
            float4 _LitTex_ST;
            float _TransitionSoftness;
            
            // Global properties set by PulverController
            float3 _PlayerWorldPos;
            float _VisionRadius;
            
            Varyings vert(Attributes input)
            {
                Varyings output;
                VertexPositionInputs vertexInput = GetVertexPositionInputs(input.positionOS.xyz);
                output.positionCS = vertexInput.positionCS;
                output.positionWS = vertexInput.positionWS;
                output.uv = TRANSFORM_TEX(input.uv, _LitTex);
                return output;
            }
            
            half4 frag(Varyings input) : SV_Target
            {
                // Calculate distance from pixel to player
                float dist = distance(input.positionWS.xy, _PlayerWorldPos.xy);
                
                // Create smooth transition between lit and unlit
                float t = smoothstep(_VisionRadius - _TransitionSoftness, _VisionRadius, dist);
                
                // Sample both textures
                half4 litColor = SAMPLE_TEXTURE2D(_LitTex, sampler_LitTex, input.uv);
                half4 unlitColor = SAMPLE_TEXTURE2D(_UnlitTex, sampler_UnlitTex, input.uv);
                
                // Blend based on distance
                return lerp(litColor, unlitColor, t);
            }
            ENDHLSL
        }
    }
    
    FallBack "Diffuse"
}