filament_math.cginc

#include "math.cginc"

#ifndef __FILAMENT_MATH_INC
#define __FILAMENT_MATH_INC

// THIS SOURCE CODE HAS BEEN MODIFIED!
// The only modifications are for compatibility with HLSL, for example:
//   * Replacing normalizeMediump() with normalize()
//   * Replacing vec3 with float3

/*
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float D_GGX(float roughness, float NoH, const float3 h) {
	// Walter et al. 2007, "Microfacet Models for Refraction through Rough Surfaces"

	// In mediump, there are two problems computing 1.0 - NoH^2
	// 1) 1.0 - NoH^2 suffers floating point cancellation when NoH^2 is close to 1 (highlights)
	// 2) NoH doesn't have enough precision around 1.0
	// Both problem can be fixed by computing 1-NoH^2 in highp and providing NoH in highp as well

	// However, we can do better using Lagrange's identity:
	//      ||a x b||^2 = ||a||^2 ||b||^2 - (a . b)^2
	// since N and H are unit vectors: ||N x H||^2 = 1.0 - NoH^2
	// This computes 1.0 - NoH^2 directly (which is close to zero in the highlights and has
	// enough precision).
	// Overall this yields better performance, keeping all computations in mediump
#if defined(TARGET_MOBILE)
	float3 NxH = cross(shading_normal, h);
	float oneMinusNoHSquared = dot(NxH, NxH);
#else
	float oneMinusNoHSquared = 1.0 - NoH * NoH;
#endif

	float a = NoH * roughness;
	float k = roughness / (oneMinusNoHSquared + a * a);
	float d = k * k * (1.0 / PI);
	return saturate(d);
}

float3 F_Schlick(const float3 f0, float VoH) {
	float f = pow(1.0 - VoH, 5.0);
	return f + f0 * (1.0 - f);
}

float V_Kelemen(float LoH) {
  // Kelemen 2001, "A Microfacet Based Coupled Specular-Matte BRDF Model with
  // Importance Sampling"
  return saturate(0.25 / (LoH * LoH));
}

float FilamentClearcoat(
    float roughness,
    float strength,
    float NoH,
    float LoH,
    float3 h) {
  float Dc = D_GGX(roughness, NoH, h);
  float Vc = V_Kelemen(LoH);
  float Fc = F_Schlick(0.04, LoH) * strength;
  return (Dc * Vc) * Fc;
}

#endif  // __FILAMENT_MATH_INC