AppleHillsProduction/Assets/Shaders/TrashMaze/RevealStamp.shader

Shader "Hidden/TrashMaze/RevealStamp"
{
    Properties
    {
        _StampPos ("Stamp Position", Vector) = (0.5, 0.5, 0, 0)
        _StampRadius ("Stamp Radius", Float) = 0.2
    }
    
    SubShader
    {
        Tags { "Queue"="Overlay" "RenderType"="Opaque" }
        
        // Additive blend to accumulate stamps
        Blend One One
        ZTest Always
        ZWrite Off
        Cull Off
        
        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
            {
                float4 positionCS : SV_POSITION;
                float2 uv : TEXCOORD0;
            };
            
            float4 _StampPos;
            float _StampRadius;
            
            Varyings vert(Attributes input)
            {
                Varyings output;
                output.positionCS = TransformObjectToHClip(input.positionOS.xyz);
                output.uv = input.uv;
                return output;
            }
            
            half4 frag(Varyings input) : SV_Target
            {
                // Calculate distance from stamp center
                float dist = distance(input.uv, _StampPos.xy);
                
                // Binary circle: 1.0 inside radius, 0.0 outside
                float alpha = dist < _StampRadius ? 1.0 : 0.0;
                
                // Return white with calculated alpha (additive blend accumulates)
                return half4(alpha, alpha, alpha, alpha);
            }
            ENDHLSL
        }
    }
}