Shader "Custom/OutlineURP"
{
    Properties
    {
        _OutlineColor ("Outline Color", Color) = (1, 1, 0, 1)
        _OutlineWidth ("Outline Width", Range(0.0, 0.05)) = 0.01
    }

    SubShader
    {
        Tags { "RenderType"="Opaque" "Queue"="Overlay" }

        Pass
        {
            Name "Outline"
            Tags { "LightMode"="UniversalForward" }

            Cull Front // Render back faces for outline

            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

            struct Attributes
            {
                float4 positionOS : POSITION;
                float3 normalOS : NORMAL;
            };

            struct Varyings
            {
                float4 positionCS : SV_POSITION;
            };

            float4 _OutlineColor;
            float _OutlineWidth;

            Varyings vert(Attributes IN)
            {
                Varyings OUT;

                // Convert object-space normal to world-space
                float3 normalWS = TransformObjectToWorldNormal(IN.normalOS);

                // Convert object-space position to world-space
                float3 positionWS = TransformObjectToWorld(IN.positionOS);

                // Expand the model along its normals for outline effect
                positionWS += normalWS * _OutlineWidth;

                // Convert world-space position to clip-space
                OUT.positionCS = TransformWorldToHClip(positionWS);
                return OUT;
            }

            half4 frag(Varyings IN) : SV_Target
            {
                return _OutlineColor; // Use user-defined outline color
            }
            ENDHLSL
        }
    }
}