URP_Fresnel.shader

URP_Fresnel.shader

Shader "Custom/URP_Fresnel"
{
    Properties
    {
        [Header(Base Settings)]
        _BaseColor ("Base Color", Color) = (0.1, 0.1, 0.15, 1.0)
        
        [Header(Fresnel Glow Settings)]
        [HDR] _GlowColor ("Glow Color", Color) = (0.0, 0.75, 1.0, 1.0)
        _FresnelPower ("Fresnel Power", Range(0.1, 10.0)) = 3.0
    }

    SubShader
    {
        Tags 
        { 
            "RenderType"="Opaque" 
            "RenderPipeline"="UniversalPipeline"
            "Queue"="Geometry"
        }

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

            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag

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

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

            struct Varyings
            {
                float4 positionCS   : SV_POSITION;
                float3 worldNormal  : TEXCOORD0;
                float3 worldViewDir : TEXCOORD1;
            };

            // Uniforms inside the SRP Batcher CBUFFER for optimization
            CBUFFER_START(UnityPerMaterial)
                float4 _BaseColor;
                float4 _GlowColor;
                float _FresnelPower;
            CBUFFER_END

            Varyings vert(Attributes input)
            {
                Varyings output = (Varyings)0;

                float3 worldPos = TransformObjectToWorld(input.positionOS.xyz);
                output.positionCS = TransformWorldToHClip(worldPos);
                output.worldNormal = TransformObjectToWorldNormal(input.normalOS);
                output.worldViewDir = GetWorldSpaceViewDir(worldPos);

                return output;
            }

            float4 frag(Varyings input) : SV_Target
            {
                // 1. Normalize interpolated vectors
                float3 N_vector = normalize(input.worldNormal);
                float3 V_vector = normalize(input.worldViewDir);

                // 2. Calculate the Dot Product between Normal and View directions
                // Saturate: clamps the dot product to 0.0 - 1.0 range
                float n_dot_v = saturate(dot(N_vector, V_vector));
                
                // 3. Fresnel formula: Invert and raise to exponential power
                float fresnel_value = pow(1.0 - n_dot_v, _FresnelPower);

                // 4. Lerp between Base color and Glow color based on the Fresnel term
                float final_color = lerp(_BaseColor, _GlowColor, fresnel_value);
                
                return final_color;
            }
            ENDHLSL
        }
    }
}