using nicer LUT dfg Fresnel in unity

dfg.shader

// https://eheitzresearch.wordpress.com/240-2/

// Generating the dfg:
// https://github.com/google/filament/blob/main/tools/cmgen/src/cmgen.cpp
// make sure to generate the multiscatter dfg


[NonModifiableTextureData] [NoScaleOffset] _DFG ("DFG Lut", 2D) = "black" {}



Texture2D_float _DFG;
SamplerState sampler_DFG;



float3 F_Schlick(float3 f0, float f90, float VoH)
{
	return f0 + (f90 - f0) * pow(1.0 - VoH, 5);
}

float3 fresnel(float3 f0, float LoH)
{
	float f90 = saturate(dot(f0, float(50.0 * 0.33).xxx));
	return F_Schlick(f0, f90, LoH);
}



// standardish fresnel

float3 fresnel;
fresnel = fresnel(f0, NoV);
fresnel *= length(indirectDiffuse);

...
// standardish way of calculating indirect specular

float3 indirectSpecular *= lerp(F, f0, perceptualRoughness) * horizon * horizon;

// standardish way of calculating direct specular

float3 specular = max(0, D * V * F * finalLight * UNITY_PI);



// dfg fresnel

float3 fresnel = fresnel(f0, NoV);
float2 dfguv = float2(NoV, perceptualRoughness);
float2 dfg = _DFG.Sample(sampler_DFG, dfguv).xy;
float3 energyCompensation = 1.0 + f0 * (1.0 / dfg.y - 1.0);

// dfg indirect specular

dfg.x *= saturate(length(indirectDiffuse)));
float3 indirectSpecular = indirectSpecular * lerp(dfg.xxx, dfg.yyy, f0) * horizon * horizon * energyCompensation;

// dfg direct specular

float3 specular = max(0, D * V * F * finalLight * energyCompensation * UNITY_PI);