Shader "Custom/URP_GlowShader"
{
    Properties {
        _Color ("Color", Color) = (1,1,1,1)
        _Size ("Atmosphere Size Multiplier", Range(0,16)) = 4
        _Rim ("Fade Power", Range(0,8)) = 4
        _Light ("Lighting Power", Range(0,10)) = 1.4
        _Ambient ("Ambient Power", Range (0,6)) = 0.8
    }
    SubShader {
        Tags { "RenderType"="Transparent" }
        LOD 200
        Cull Front

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

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

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

               struct Varyings {
                   float4 positionHCS : SV_POSITION;
                   float3 normalWS    : TEXCOORD0;
                   float3 viewDirWS   : TEXCOORD1;
                   float fogFactor    : TEXCOORD2;
               };

            CBUFFER_START(UnityPerMaterial)
                float4 _Color;
                float _Size;
                float _Rim;
                float _Light;
                float _Ambient;
            CBUFFER_END

            Varyings vert(Attributes IN)
            {
                Varyings OUT;
                float3 scaled = IN.positionOS.xyz + IN.positionOS.xyz * (_Size / 10.0);
                OUT.positionHCS = TransformObjectToHClip(scaled);
                float3 normalWS = TransformObjectToWorldNormal(-IN.normalOS); // Invert normal
                OUT.normalWS = normalWS;
                OUT.viewDirWS = normalize(_WorldSpaceCameraPos - TransformObjectToWorld(scaled));
                OUT.fogFactor = ComputeFogFactor(OUT.positionHCS.z / OUT.positionHCS.w);
                return OUT;
            }

            float4 frag(Varyings IN) : SV_Target
            {
                float rim = saturate(dot(normalize(IN.viewDirWS), IN.normalWS));
                float alpha = lerp(0, 1, pow(rim, _Rim));

                // Lighting: simple negative lambert
                float3 lightDir = normalize(_MainLightPosition.xyz);
                float diff = max(0, dot(-IN.normalWS, lightDir)) * _Light + _Ambient;
                float3 color = _Color.rgb * _MainLightColor.rgb * diff;
                color = MixFog(color, IN.fogFactor);
                return float4(color, alpha * _Color.a);
            }
            ENDHLSL
        }
    }
    FallBack "Universal Forward"
}