/*
 * Adapted from Open Shading Language with this license:
 *
 * Copyright (c) 2009-2010 Sony Pictures Imageworks Inc., et al.
 * All Rights Reserved.
 *
 * Modifications Copyright 2011, Blender Foundation.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 * * Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * * Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * * Neither the name of Sony Pictures Imageworks nor the names of its
 *   contributors may be used to endorse or promote products derived from
 *   this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef __BSDF_MICROFACET_H__
#define __BSDF_MICROFACET_H__

CCL_NAMESPACE_BEGIN

typedef ccl_addr_space struct MicrofacetExtra {
	float3 color;
} MicrofacetExtra;

typedef ccl_addr_space struct MicrofacetBsdf {
	SHADER_CLOSURE_BASE;

	float alpha_x, alpha_y, ior;
	MicrofacetExtra *extra;
	float3 T;
	float3 N;
} MicrofacetBsdf;

/* Beckmann and GGX microfacet importance sampling. */

ccl_device_inline void microfacet_beckmann_sample_slopes(
	KernelGlobals *kg,
	const float cos_theta_i, const float sin_theta_i,
	float randu, float randv, float *slope_x, float *slope_y,
	float *G1i)
{
	/* special case (normal incidence) */
	if(cos_theta_i >= 0.99999f) {
		const float r = sqrtf(-logf(randu));
		const float phi = M_2PI_F * randv;
		*slope_x = r * cosf(phi);
		*slope_y = r * sinf(phi);
		*G1i = 1.0f;
		return;
	}

	/* precomputations */
	const float tan_theta_i = sin_theta_i/cos_theta_i;
	const float inv_a = tan_theta_i;
	const float cot_theta_i = 1.0f/tan_theta_i;
	const float erf_a = fast_erff(cot_theta_i);
	const float exp_a2 = expf(-cot_theta_i*cot_theta_i);
	const float SQRT_PI_INV = 0.56418958354f;
	const float Lambda = 0.5f*(erf_a - 1.0f) + (0.5f*SQRT_PI_INV)*(exp_a2*inv_a);
	const float G1 = 1.0f/(1.0f + Lambda); /* masking */

	*G1i = G1;

#if defined(__KERNEL_GPU__)
	/* Based on paper from Wenzel Jakob
	 * An Improved Visible Normal Sampling Routine for the Beckmann Distribution
	 *
	 * http://www.mitsuba-renderer.org/~wenzel/files/visnormal.pdf
	 *
	 * Reformulation from OpenShadingLanguage which avoids using inverse
	 * trigonometric functions.
	 */

	/* Sample slope X.
	 *
	 * Compute a coarse approximation using the approximation:
	 *   exp(-ierf(x)^2) ~= 1 - x * x
	 *   solve y = 1 + b + K * (1 - b * b)
	 */
	float K = tan_theta_i * SQRT_PI_INV;
	float y_approx = randu * (1.0f + erf_a + K * (1 - erf_a * erf_a));
	float y_exact  = randu * (1.0f + erf_a + K * exp_a2);
	float b = K > 0 ? (0.5f - sqrtf(K * (K - y_approx + 1.0f) + 0.25f)) / K : y_approx - 1.0f;

	/* Perform newton step to refine toward the true root. */
	float inv_erf = fast_ierff(b);
	float value  = 1.0f + b + K * expf(-inv_erf * inv_erf) - y_exact;
	/* Check if we are close enough already,
	 * this also avoids NaNs as we get close to the root.
	 */
	if(fabsf(value) > 1e-6f) {
		b -= value / (1.0f - inv_erf * tan_theta_i); /* newton step 1. */
		inv_erf = fast_ierff(b);
		value  = 1.0f + b + K * expf(-inv_erf * inv_erf) - y_exact;
		b -= value / (1.0f - inv_erf * tan_theta_i); /* newton step 2. */
		/* Compute the slope from the refined value. */
		*slope_x = fast_ierff(b);
	}
	else {
		/* We are close enough already. */
		*slope_x = inv_erf;
	}
	*slope_y = fast_ierff(2.0f*randv - 1.0f);
#else
	/* Use precomputed table on CPU, it gives better perfomance. */
	int beckmann_table_offset = kernel_data.tables.beckmann_offset;

	*slope_x = lookup_table_read_2D(kg, randu, cos_theta_i,
		beckmann_table_offset, BECKMANN_TABLE_SIZE, BECKMANN_TABLE_SIZE);
	*slope_y = fast_ierff(2.0f*randv - 1.0f);
#endif
}

/* GGX microfacet importance sampling from:
 *
 * Importance Sampling Microfacet-Based BSDFs using the Distribution of Visible Normals.
 * E. Heitz and E. d'Eon, EGSR 2014
 */

ccl_device_inline void microfacet_ggx_sample_slopes(
	const float cos_theta_i, const float sin_theta_i,
	float randu, float randv, float *slope_x, float *slope_y,
	float *G1i)
{
	/* special case (normal incidence) */
	if(cos_theta_i >= 0.99999f) {
		const float r = sqrtf(randu/(1.0f - randu));
		const float phi = M_2PI_F * randv;
		*slope_x = r * cosf(phi);
		*slope_y = r * sinf(phi);
		*G1i = 1.0f;

		return;
	}

	/* precomputations */
	const float tan_theta_i = sin_theta_i/cos_theta_i;
	const float G1_inv = 0.5f * (1.0f + safe_sqrtf(1.0f + tan_theta_i*tan_theta_i));

	*G1i = 1.0f/G1_inv;

	/* sample slope_x */
	const float A = 2.0f*randu*G1_inv - 1.0f;
	const float AA = A*A;
	const float tmp = 1.0f/(AA - 1.0f);
	const float B = tan_theta_i;
	const float BB = B*B;
	const float D = safe_sqrtf(BB*(tmp*tmp) - (AA - BB)*tmp);
	const float slope_x_1 = B*tmp - D;
	const float slope_x_2 = B*tmp + D;
	*slope_x = (A < 0.0f || slope_x_2*tan_theta_i > 1.0f)? slope_x_1: slope_x_2;

	/* sample slope_y */
	float S;

	if(randv > 0.5f) {
		S = 1.0f;
		randv = 2.0f*(randv - 0.5f);
	}
	else {
		S = -1.0f;
		randv = 2.0f*(0.5f - randv);
	}

	const float z = (randv*(randv*(randv*0.27385f - 0.73369f) + 0.46341f)) / (randv*(randv*(randv*0.093073f + 0.309420f) - 1.000000f) + 0.597999f);
	*slope_y = S * z * safe_sqrtf(1.0f + (*slope_x)*(*slope_x));
}

ccl_device_forceinline float3 microfacet_sample_stretched(
	KernelGlobals *kg, const float3 omega_i,
	const float alpha_x, const float alpha_y,
	const float randu, const float randv,
	bool beckmann, float *G1i)
{
	/* 1. stretch omega_i */
	float3 omega_i_ = make_float3(alpha_x * omega_i.x, alpha_y * omega_i.y, omega_i.z);
	omega_i_ = normalize(omega_i_);

	/* get polar coordinates of omega_i_ */
	float costheta_ = 1.0f;
	float sintheta_ = 0.0f;
	float cosphi_ = 1.0f;
	float sinphi_ = 0.0f;

	if(omega_i_.z < 0.99999f) {
		costheta_ = omega_i_.z;
		sintheta_ = safe_sqrtf(1.0f - costheta_*costheta_);

		float invlen = 1.0f/sintheta_;
		cosphi_ = omega_i_.x * invlen;
		sinphi_ = omega_i_.y * invlen;
	}

	/* 2. sample P22_{omega_i}(x_slope, y_slope, 1, 1) */
	float slope_x, slope_y;

	if(beckmann) {
		microfacet_beckmann_sample_slopes(kg, costheta_, sintheta_,
			randu, randv, &slope_x, &slope_y, G1i);
	}
	else {
		microfacet_ggx_sample_slopes(costheta_, sintheta_,
			randu, randv, &slope_x, &slope_y, G1i);
	}

	/* 3. rotate */
	float tmp = cosphi_*slope_x - sinphi_*slope_y;
	slope_y = sinphi_*slope_x + cosphi_*slope_y;
	slope_x = tmp;

	/* 4. unstretch */
	slope_x = alpha_x * slope_x;
	slope_y = alpha_y * slope_y;

	/* 5. compute normal */
	return normalize(make_float3(-slope_x, -slope_y, 1.0f));
} 

/* GGX microfacet with Smith shadow-masking from:
 *
 * Microfacet Models for Refraction through Rough Surfaces
 * B. Walter, S. R. Marschner, H. Li, K. E. Torrance, EGSR 2007
 *
 * Anisotropic from:
 *
 * Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs
 * E. Heitz, Research Report 2014
 *
 * Anisotropy is only supported for reflection currently, but adding it for
 * transmission is just a matter of copying code from reflection if needed. */

ccl_device int bsdf_microfacet_ggx_setup(MicrofacetBsdf *bsdf)
{
	bsdf->alpha_x = saturate(bsdf->alpha_x);
	bsdf->alpha_y = bsdf->alpha_x;
	
	bsdf->type = CLOSURE_BSDF_MICROFACET_GGX_ID;

	return SD_BSDF|SD_BSDF_HAS_EVAL;
}

ccl_device bool bsdf_microfacet_merge(const ShaderClosure *a, const ShaderClosure *b)
{
	const MicrofacetBsdf *bsdf_a = (const MicrofacetBsdf*)a;
	const MicrofacetBsdf *bsdf_b = (const MicrofacetBsdf*)b;

	return (isequal_float3(bsdf_a->N, bsdf_b->N)) &&
	       (bsdf_a->alpha_x == bsdf_b->alpha_x) &&
	       (bsdf_a->alpha_y == bsdf_b->alpha_y) &&
	       (isequal_float3(bsdf_a->T, bsdf_b->T)) &&
	       (bsdf_a->ior == bsdf_b->ior) &&
	       ((!bsdf_a->extra && !bsdf_b->extra) ||
	        ((bsdf_a->extra && bsdf_b->extra) &&
	         (isequal_float3(bsdf_a->extra->color, bsdf_b->extra->color))));
}

ccl_device int bsdf_microfacet_ggx_aniso_setup(MicrofacetBsdf *bsdf)
{
	bsdf->alpha_x = saturate(bsdf->alpha_x);
	bsdf->alpha_y = saturate(bsdf->alpha_y);
	
	bsdf->type = CLOSURE_BSDF_MICROFACET_GGX_ANISO_ID;

	return SD_BSDF|SD_BSDF_HAS_EVAL;
}

ccl_device int bsdf_microfacet_ggx_refraction_setup(MicrofacetBsdf *bsdf)
{
	bsdf->alpha_x = saturate(bsdf->alpha_x);
	bsdf->alpha_y = bsdf->alpha_x;

	bsdf->type = CLOSURE_BSDF_MICROFACET_GGX_REFRACTION_ID;

	return SD_BSDF|SD_BSDF_HAS_EVAL;
}

ccl_device void bsdf_microfacet_ggx_blur(ShaderClosure *sc, float roughness)
{
	MicrofacetBsdf *bsdf = (MicrofacetBsdf*)sc;

	bsdf->alpha_x = fmaxf(roughness, bsdf->alpha_x);
	bsdf->alpha_y = fmaxf(roughness, bsdf->alpha_y);
}

ccl_device float3 bsdf_microfacet_ggx_eval_reflect(const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
{
	const MicrofacetBsdf *bsdf = (const MicrofacetBsdf*)sc;
	float alpha_x = bsdf->alpha_x;
	float alpha_y = bsdf->alpha_y;
	bool m_refractive = bsdf->type == CLOSURE_BSDF_MICROFACET_GGX_REFRACTION_ID;
	float3 N = bsdf->N;

	if(m_refractive || alpha_x*alpha_y <= 1e-7f)
		return make_float3(0.0f, 0.0f, 0.0f);

	float cosNO = dot(N, I);
	float cosNI = dot(N, omega_in);

	if(cosNI > 0 && cosNO > 0) {
		/* get half vector */
		float3 m = normalize(omega_in + I);
		float alpha2 = alpha_x * alpha_y;
		float D, G1o, G1i;

		if(alpha_x == alpha_y) {
			/* isotropic
			 * eq. 20: (F*G*D)/(4*in*on)
			 * eq. 33: first we calculate D(m) */
			float cosThetaM = dot(N, m);
			float cosThetaM2 = cosThetaM * cosThetaM;
			float cosThetaM4 = cosThetaM2 * cosThetaM2;
			float tanThetaM2 = (1 - cosThetaM2) / cosThetaM2;
			D = alpha2 / (M_PI_F * cosThetaM4 * (alpha2 + tanThetaM2) * (alpha2 + tanThetaM2));

			/* eq. 34: now calculate G1(i,m) and G1(o,m) */
			G1o = 2 / (1 + safe_sqrtf(1 + alpha2 * (1 - cosNO * cosNO) / (cosNO * cosNO)));
			G1i = 2 / (1 + safe_sqrtf(1 + alpha2 * (1 - cosNI * cosNI) / (cosNI * cosNI))); 
		}
		else {
			/* anisotropic */
			float3 X, Y, Z = N;
			make_orthonormals_tangent(Z, bsdf->T, &X, &Y);

			/* distribution */
			float3 local_m = make_float3(dot(X, m), dot(Y, m), dot(Z, m));
			float slope_x = -local_m.x/(local_m.z*alpha_x);
			float slope_y = -local_m.y/(local_m.z*alpha_y);
			float slope_len = 1 + slope_x*slope_x + slope_y*slope_y;

			float cosThetaM = local_m.z;
			float cosThetaM2 = cosThetaM * cosThetaM;
			float cosThetaM4 = cosThetaM2 * cosThetaM2;

			D = 1 / ((slope_len * slope_len) * M_PI_F * alpha2 * cosThetaM4);

			/* G1(i,m) and G1(o,m) */
			float tanThetaO2 = (1 - cosNO * cosNO) / (cosNO * cosNO);
			float cosPhiO = dot(I, X);
			float sinPhiO = dot(I, Y);

			float alphaO2 = (cosPhiO*cosPhiO)*(alpha_x*alpha_x) + (sinPhiO*sinPhiO)*(alpha_y*alpha_y);
			alphaO2 /= cosPhiO*cosPhiO + sinPhiO*sinPhiO;

			G1o = 2 / (1 + safe_sqrtf(1 + alphaO2 * tanThetaO2));

			float tanThetaI2 = (1 - cosNI * cosNI) / (cosNI * cosNI);
			float cosPhiI = dot(omega_in, X);
			float sinPhiI = dot(omega_in, Y);

			float alphaI2 = (cosPhiI*cosPhiI)*(alpha_x*alpha_x) + (sinPhiI*sinPhiI)*(alpha_y*alpha_y);
			alphaI2 /= cosPhiI*cosPhiI + sinPhiI*sinPhiI;

			G1i = 2 / (1 + safe_sqrtf(1 + alphaI2 * tanThetaI2));
		}

		float G = G1o * G1i;

		/* eq. 20 */
		float common = D * 0.25f / cosNO;
		float out = G * common;

		/* eq. 2 in distribution of visible normals sampling
		 * pm = Dw = G1o * dot(m, I) * D / dot(N, I); */

		/* eq. 38 - but see also:
		 * eq. 17 in http://www.graphics.cornell.edu/~bjw/wardnotes.pdf
		 * pdf = pm * 0.25 / dot(m, I); */
		*pdf = G1o * common;

		return make_float3(out, out, out);
	}

	return make_float3(0.0f, 0.0f, 0.0f);
}

ccl_device float3 bsdf_microfacet_ggx_eval_transmit(const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
{
	const MicrofacetBsdf *bsdf = (const MicrofacetBsdf*)sc;
	float alpha_x = bsdf->alpha_x;
	float alpha_y = bsdf->alpha_y;
	float m_eta = bsdf->ior;
	bool m_refractive = bsdf->type == CLOSURE_BSDF_MICROFACET_GGX_REFRACTION_ID;
	float3 N = bsdf->N;

	if(!m_refractive || alpha_x*alpha_y <= 1e-7f)
		return make_float3(0.0f, 0.0f, 0.0f);

	float cosNO = dot(N, I);
	float cosNI = dot(N, omega_in);

	if(cosNO <= 0 || cosNI >= 0)
		return make_float3(0.0f, 0.0f, 0.0f); /* vectors on same side -- not possible */

	/* compute half-vector of the refraction (eq. 16) */
	float3 ht = -(m_eta * omega_in + I);
	float3 Ht = normalize(ht);
	float cosHO = dot(Ht, I);
	float cosHI = dot(Ht, omega_in);

	float D, G1o, G1i;

	/* eq. 33: first we calculate D(m) with m=Ht: */
	float alpha2 = alpha_x * alpha_y;
	float cosThetaM = dot(N, Ht);
	float cosThetaM2 = cosThetaM * cosThetaM;
	float tanThetaM2 = (1 - cosThetaM2) / cosThetaM2;
	float cosThetaM4 = cosThetaM2 * cosThetaM2;
	D = alpha2 / (M_PI_F * cosThetaM4 * (alpha2 + tanThetaM2) * (alpha2 + tanThetaM2));

	/* eq. 34: now calculate G1(i,m) and G1(o,m) */
	G1o = 2 / (1 + safe_sqrtf(1 + alpha2 * (1 - cosNO * cosNO) / (cosNO * cosNO)));
	G1i = 2 / (1 + safe_sqrtf(1 + alpha2 * (1 - cosNI * cosNI) / (cosNI * cosNI))); 

	float G = G1o * G1i;

	/* probability */
	float Ht2 = dot(ht, ht);

	/* eq. 2 in distribution of visible normals sampling
	 * pm = Dw = G1o * dot(m, I) * D / dot(N, I); */

	/* out = fabsf(cosHI * cosHO) * (m_eta * m_eta) * G * D / (cosNO * Ht2)
	 * pdf = pm * (m_eta * m_eta) * fabsf(cosHI) / Ht2 */
	float common = D * (m_eta * m_eta) / (cosNO * Ht2);
	float out = G * fabsf(cosHI * cosHO) * common;
	*pdf = G1o * fabsf(cosHO * cosHI) * common;

	return make_float3(out, out, out);
}

ccl_device int bsdf_microfacet_ggx_sample(KernelGlobals *kg, const ShaderClosure *sc, float3 Ng, float3 I, float3 dIdx, float3 dIdy, float randu, float randv, float3 *eval, float3 *omega_in, float3 *domega_in_dx, float3 *domega_in_dy, float *pdf)
{
	const MicrofacetBsdf *bsdf = (const MicrofacetBsdf*)sc;
	float alpha_x = bsdf->alpha_x;
	float alpha_y = bsdf->alpha_y;
	bool m_refractive = bsdf->type == CLOSURE_BSDF_MICROFACET_GGX_REFRACTION_ID;
	float3 N = bsdf->N;

	float cosNO = dot(N, I);
	if(cosNO > 0) {
		float3 X, Y, Z = N;

		if(alpha_x == alpha_y)
			make_orthonormals(Z, &X, &Y);
		else
			make_orthonormals_tangent(Z, bsdf->T, &X, &Y);

		/* importance sampling with distribution of visible normals. vectors are
		 * transformed to local space before and after */
		float3 local_I = make_float3(dot(X, I), dot(Y, I), cosNO);
		float3 local_m;
		float G1o;

		local_m = microfacet_sample_stretched(kg, local_I, alpha_x, alpha_y,
			randu, randv, false, &G1o);

		float3 m = X*local_m.x + Y*local_m.y + Z*local_m.z;
		float cosThetaM = local_m.z;

		/* reflection or refraction? */
		if(!m_refractive) {
			float cosMO = dot(m, I);

			if(cosMO > 0) {
				/* eq. 39 - compute actual reflected direction */
				*omega_in = 2 * cosMO * m - I;

				if(dot(Ng, *omega_in) > 0) {
					if(alpha_x*alpha_y <= 1e-7f) {
						/* some high number for MIS */
						*pdf = 1e6f;
						*eval = make_float3(1e6f, 1e6f, 1e6f);
					}
					else {
						/* microfacet normal is visible to this ray */
						/* eq. 33 */
						float alpha2 = alpha_x * alpha_y;
						float D, G1i;

						if(alpha_x == alpha_y) {
							/* isotropic */
							float cosThetaM2 = cosThetaM * cosThetaM;
							float cosThetaM4 = cosThetaM2 * cosThetaM2;
							float tanThetaM2 = 1/(cosThetaM2) - 1;
							D = alpha2 / (M_PI_F * cosThetaM4 * (alpha2 + tanThetaM2) * (alpha2 + tanThetaM2));

							/* eval BRDF*cosNI */
							float cosNI = dot(N, *omega_in);

							/* eq. 34: now calculate G1(i,m) */
							G1i = 2 / (1 + safe_sqrtf(1 + alpha2 * (1 - cosNI * cosNI) / (cosNI * cosNI))); 
						}
						else {
							/* anisotropic distribution */
							float3 local_m = make_float3(dot(X, m), dot(Y, m), dot(Z, m));
							float slope_x = -local_m.x/(local_m.z*alpha_x);
							float slope_y = -local_m.y/(local_m.z*alpha_y);
							float slope_len = 1 + slope_x*slope_x + slope_y*slope_y;

							float cosThetaM = local_m.z;
							float cosThetaM2 = cosThetaM * cosThetaM;
							float cosThetaM4 = cosThetaM2 * cosThetaM2;

							D = 1 / ((slope_len * slope_len) * M_PI_F * alpha2 * cosThetaM4);

							/* calculate G1(i,m) */
							float cosNI = dot(N, *omega_in);

							float tanThetaI2 = (1 - cosNI * cosNI) / (cosNI * cosNI);
							float cosPhiI = dot(*omega_in, X);
							float sinPhiI = dot(*omega_in, Y);

							float alphaI2 = (cosPhiI*cosPhiI)*(alpha_x*alpha_x) + (sinPhiI*sinPhiI)*(alpha_y*alpha_y);
							alphaI2 /= cosPhiI*cosPhiI + sinPhiI*sinPhiI;

							G1i = 2 / (1 + safe_sqrtf(1 + alphaI2 * tanThetaI2));
						}

						/* see eval function for derivation */
						float common = (G1o * D) * 0.25f / cosNO;
						float out = G1i * common;
						*pdf = common;

						*eval = make_float3(out, out, out);
					}

#ifdef __RAY_DIFFERENTIALS__
					*domega_in_dx = (2 * dot(m, dIdx)) * m - dIdx;
					*domega_in_dy = (2 * dot(m, dIdy)) * m - dIdy;
#endif
				}
			}
		}
		else {
			/* CAUTION: the i and o variables are inverted relative to the paper
			 * eq. 39 - compute actual refractive direction */
			float3 R, T;
#ifdef __RAY_DIFFERENTIALS__
			float3 dRdx, dRdy, dTdx, dTdy;
#endif
			float m_eta = bsdf->ior, fresnel;
			bool inside;

			fresnel = fresnel_dielectric(m_eta, m, I, &R, &T,
#ifdef __RAY_DIFFERENTIALS__
				dIdx, dIdy, &dRdx, &dRdy, &dTdx, &dTdy,
#endif
				&inside);
			
			if(!inside && fresnel != 1.0f) {

				*omega_in = T;
#ifdef __RAY_DIFFERENTIALS__
				*domega_in_dx = dTdx;
				*domega_in_dy = dTdy;
#endif

				if(alpha_x*alpha_y <= 1e-7f || fabsf(m_eta - 1.0f) < 1e-4f) {
					/* some high number for MIS */
					*pdf = 1e6f;
					*eval = make_float3(1e6f, 1e6f, 1e6f);
				}
				else {
					/* eq. 33 */
					float alpha2 = alpha_x * alpha_y;
					float cosThetaM2 = cosThetaM * cosThetaM;
					float cosThetaM4 = cosThetaM2 * cosThetaM2;
					float tanThetaM2 = 1/(cosThetaM2) - 1;
					float D = alpha2 / (M_PI_F * cosThetaM4 * (alpha2 + tanThetaM2) * (alpha2 + tanThetaM2));

					/* eval BRDF*cosNI */
					float cosNI = dot(N, *omega_in);

					/* eq. 34: now calculate G1(i,m) */
					float G1i = 2 / (1 + safe_sqrtf(1 + alpha2 * (1 - cosNI * cosNI) / (cosNI * cosNI))); 

					/* eq. 21 */
					float cosHI = dot(m, *omega_in);
					float cosHO = dot(m, I);
					float Ht2 = m_eta * cosHI + cosHO;
					Ht2 *= Ht2;

					/* see eval function for derivation */
					float common = (G1o * D) * (m_eta * m_eta) / (cosNO * Ht2);
					float out = G1i * fabsf(cosHI * cosHO) * common;
					*pdf = cosHO * fabsf(cosHI) * common;

					*eval = make_float3(out, out, out);
				}
			}
		}
	}
	return (m_refractive) ? LABEL_TRANSMIT|LABEL_GLOSSY : LABEL_REFLECT|LABEL_GLOSSY;
}

/* Beckmann microfacet with Smith shadow-masking from:
 *
 * Microfacet Models for Refraction through Rough Surfaces
 * B. Walter, S. R. Marschner, H. Li, K. E. Torrance, EGSR 2007 */

ccl_device int bsdf_microfacet_beckmann_setup(MicrofacetBsdf *bsdf)
{
	bsdf->alpha_x = saturate(bsdf->alpha_x);
	bsdf->alpha_y = bsdf->alpha_x;

	bsdf->type = CLOSURE_BSDF_MICROFACET_BECKMANN_ID;
	return SD_BSDF|SD_BSDF_HAS_EVAL;
}

ccl_device int bsdf_microfacet_beckmann_aniso_setup(MicrofacetBsdf *bsdf)
{
	bsdf->alpha_x = saturate(bsdf->alpha_x);
	bsdf->alpha_y = saturate(bsdf->alpha_y);

	bsdf->type = CLOSURE_BSDF_MICROFACET_BECKMANN_ANISO_ID;
	return SD_BSDF|SD_BSDF_HAS_EVAL;
}

ccl_device int bsdf_microfacet_beckmann_refraction_setup(MicrofacetBsdf *bsdf)
{
	bsdf->alpha_x = saturate(bsdf->alpha_x);
	bsdf->alpha_y = bsdf->alpha_x;

	bsdf->type = CLOSURE_BSDF_MICROFACET_BECKMANN_REFRACTION_ID;
	return SD_BSDF|SD_BSDF_HAS_EVAL;
}

ccl_device void bsdf_microfacet_beckmann_blur(ShaderClosure *sc, float roughness)
{
	MicrofacetBsdf *bsdf = (MicrofacetBsdf*)sc;

	bsdf->alpha_x = fmaxf(roughness, bsdf->alpha_x);
	bsdf->alpha_y = fmaxf(roughness, bsdf->alpha_y);
}

ccl_device_inline float bsdf_beckmann_G1(float alpha, float cos_n)
{
	cos_n *= cos_n;
	float invA = alpha * safe_sqrtf((1.0f - cos_n) / cos_n);
	if(invA < 0.625f) {
		return 1.0f;
	}

	float a = 1.0f / invA;
	return ((2.181f*a + 3.535f)*a) / ((2.577f*a + 2.276f)*a + 1.0f);
}

ccl_device_inline float bsdf_beckmann_aniso_G1(float alpha_x, float alpha_y, float cos_n, float cos_phi, float sin_phi)
{
	cos_n *= cos_n;
	sin_phi *= sin_phi;
	cos_phi *= cos_phi;
	alpha_x *= alpha_x;
	alpha_y *= alpha_y;

	float alphaO2 = (cos_phi*alpha_x + sin_phi*alpha_y) / (cos_phi + sin_phi);
	float invA = safe_sqrtf(alphaO2 * (1 - cos_n) / cos_n);
	if(invA < 0.625f) {
		return 1.0f;
	}

	float a = 1.0f / invA;
	return ((2.181f*a + 3.535f)*a) / ((2.577f*a + 2.276f)*a + 1.0f);
}

ccl_device float3 bsdf_microfacet_beckmann_eval_reflect(const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
{
	const MicrofacetBsdf *bsdf = (const MicrofacetBsdf*)sc;
	float alpha_x = bsdf->alpha_x;
	float alpha_y = bsdf->alpha_y;
	bool m_refractive = bsdf->type == CLOSURE_BSDF_MICROFACET_BECKMANN_REFRACTION_ID;
	float3 N = bsdf->N;

	if(m_refractive || alpha_x*alpha_y <= 1e-7f)
		return make_float3(0.0f, 0.0f, 0.0f);

	float cosNO = dot(N, I);
	float cosNI = dot(N, omega_in);

	if(cosNO > 0 && cosNI > 0) {
		/* get half vector */
		float3 m = normalize(omega_in + I);

		float alpha2 = alpha_x * alpha_y;
		float D, G1o, G1i;

		if(alpha_x == alpha_y) {
			/* isotropic
			 * eq. 20: (F*G*D)/(4*in*on)
			 * eq. 25: first we calculate D(m) */
			float cosThetaM = dot(N, m);
			float cosThetaM2 = cosThetaM * cosThetaM;
			float tanThetaM2 = (1 - cosThetaM2) / cosThetaM2;
			float cosThetaM4 = cosThetaM2 * cosThetaM2;
			D = expf(-tanThetaM2 / alpha2) / (M_PI_F * alpha2 * cosThetaM4);

			/* eq. 26, 27: now calculate G1(i,m) and G1(o,m) */
			G1o = bsdf_beckmann_G1(alpha_x, cosNO);
			G1i = bsdf_beckmann_G1(alpha_x, cosNI);
		}
		else {
			/* anisotropic */
			float3 X, Y, Z = N;
			make_orthonormals_tangent(Z, bsdf->T, &X, &Y);

			/* distribution */
			float3 local_m = make_float3(dot(X, m), dot(Y, m), dot(Z, m));
			float slope_x = -local_m.x/(local_m.z*alpha_x);
			float slope_y = -local_m.y/(local_m.z*alpha_y);

			float cosThetaM = local_m.z;
			float cosThetaM2 = cosThetaM * cosThetaM;
			float cosThetaM4 = cosThetaM2 * cosThetaM2;

			D = expf(-slope_x*slope_x - slope_y*slope_y) / (M_PI_F * alpha2 * cosThetaM4);

			/* G1(i,m) and G1(o,m) */
			G1o = bsdf_beckmann_aniso_G1(alpha_x, alpha_y, cosNO, dot(I, X), dot(I, Y));
			G1i = bsdf_beckmann_aniso_G1(alpha_x, alpha_y, cosNI, dot(omega_in, X), dot(omega_in, Y));
		}

		float G = G1o * G1i;

		/* eq. 20 */
		float common = D * 0.25f / cosNO;
		float out = G * common;

		/* eq. 2 in distribution of visible normals sampling
		 * pm = Dw = G1o * dot(m, I) * D / dot(N, I); */

		/* eq. 38 - but see also:
		 * eq. 17 in http://www.graphics.cornell.edu/~bjw/wardnotes.pdf
		 * pdf = pm * 0.25 / dot(m, I); */
		*pdf = G1o * common;

		return make_float3(out, out, out);
	}

	return make_float3(0.0f, 0.0f, 0.0f);
}

ccl_device float3 bsdf_microfacet_beckmann_eval_transmit(const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
{
	const MicrofacetBsdf *bsdf = (const MicrofacetBsdf*)sc;
	float alpha_x = bsdf->alpha_x;
	float alpha_y = bsdf->alpha_y;
	float m_eta = bsdf->ior;
	bool m_refractive = bsdf->type == CLOSURE_BSDF_MICROFACET_BECKMANN_REFRACTION_ID;
	float3 N = bsdf->N;

	if(!m_refractive || alpha_x*alpha_y <= 1e-7f)
		return make_float3(0.0f, 0.0f, 0.0f);

	float cosNO = dot(N, I);
	float cosNI = dot(N, omega_in);

	if(cosNO <= 0 || cosNI >= 0)
		return make_float3(0.0f, 0.0f, 0.0f);

	/* compute half-vector of the refraction (eq. 16) */
	float3 ht = -(m_eta * omega_in + I);
	float3 Ht = normalize(ht);
	float cosHO = dot(Ht, I);
	float cosHI = dot(Ht, omega_in);

	/* eq. 25: first we calculate D(m) with m=Ht: */
	float alpha2 = alpha_x * alpha_y;
	float cosThetaM = min(dot(N, Ht), 1.0f);
	float cosThetaM2 = cosThetaM * cosThetaM;
	float tanThetaM2 = (1 - cosThetaM2) / cosThetaM2;
	float cosThetaM4 = cosThetaM2 * cosThetaM2;
	float D = expf(-tanThetaM2 / alpha2) / (M_PI_F * alpha2 *  cosThetaM4);

	/* eq. 26, 27: now calculate G1(i,m) and G1(o,m) */
	float G1o = bsdf_beckmann_G1(alpha_x, cosNO);
	float G1i = bsdf_beckmann_G1(alpha_x, cosNI);
	float G = G1o * G1i;

	/* probability */
	float Ht2 = dot(ht, ht);

	/* eq. 2 in distribution of visible normals sampling
	 * pm = Dw = G1o * dot(m, I) * D / dot(N, I); */

	/* out = fabsf(cosHI * cosHO) * (m_eta * m_eta) * G * D / (cosNO * Ht2)
	 * pdf = pm * (m_eta * m_eta) * fabsf(cosHI) / Ht2 */
	float common = D * (m_eta * m_eta) / (cosNO * Ht2);
	float out = G * fabsf(cosHI * cosHO) * common;
	*pdf = G1o * fabsf(cosHO * cosHI) * common;

	return make_float3(out, out, out);
}

ccl_device int bsdf_microfacet_beckmann_sample(KernelGlobals *kg, const ShaderClosure *sc, float3 Ng, float3 I, float3 dIdx, float3 dIdy, float randu, float randv, float3 *eval, float3 *omega_in, float3 *domega_in_dx, float3 *domega_in_dy, float *pdf)
{
	const MicrofacetBsdf *bsdf = (const MicrofacetBsdf*)sc;
	float alpha_x = bsdf->alpha_x;
	float alpha_y = bsdf->alpha_y;
	bool m_refractive = bsdf->type == CLOSURE_BSDF_MICROFACET_BECKMANN_REFRACTION_ID;
	float3 N = bsdf->N;

	float cosNO = dot(N, I);
	if(cosNO > 0) {
		float3 X, Y, Z = N;

		if(alpha_x == alpha_y)
			make_orthonormals(Z, &X, &Y);
		else
			make_orthonormals_tangent(Z, bsdf->T, &X, &Y);

		/* importance sampling with distribution of visible normals. vectors are
		 * transformed to local space before and after */
		float3 local_I = make_float3(dot(X, I), dot(Y, I), cosNO);
		float3 local_m;
		float G1o;

		local_m = microfacet_sample_stretched(kg, local_I, alpha_x, alpha_x,
			randu, randv, true, &G1o);

		float3 m = X*local_m.x + Y*local_m.y + Z*local_m.z;
		float cosThetaM = local_m.z;

		/* reflection or refraction? */
		if(!m_refractive) {
			float cosMO = dot(m, I);

			if(cosMO > 0) {
				/* eq. 39 - compute actual reflected direction */
				*omega_in = 2 * cosMO * m - I;

				if(dot(Ng, *omega_in) > 0) {
					if(alpha_x*alpha_y <= 1e-7f) {
						/* some high number for MIS */
						*pdf = 1e6f;
						*eval = make_float3(1e6f, 1e6f, 1e6f);
					}
					else {
						/* microfacet normal is visible to this ray
						 * eq. 25 */
						float alpha2 = alpha_x * alpha_y;
						float D, G1i;

						if(alpha_x == alpha_y) {
							/* istropic distribution */
							float cosThetaM2 = cosThetaM * cosThetaM;
							float cosThetaM4 = cosThetaM2 * cosThetaM2;
							float tanThetaM2 = 1/(cosThetaM2) - 1;
							D = expf(-tanThetaM2 / alpha2) / (M_PI_F * alpha2 *  cosThetaM4);

							/* eval BRDF*cosNI */
							float cosNI = dot(N, *omega_in);

							/* eq. 26, 27: now calculate G1(i,m) */
							G1i = bsdf_beckmann_G1(alpha_x, cosNI);
						}
						else {
							/* anisotropic distribution */
							float3 local_m = make_float3(dot(X, m), dot(Y, m), dot(Z, m));
							float slope_x = -local_m.x/(local_m.z*alpha_x);
							float slope_y = -local_m.y/(local_m.z*alpha_y);

							float cosThetaM = local_m.z;
							float cosThetaM2 = cosThetaM * cosThetaM;
							float cosThetaM4 = cosThetaM2 * cosThetaM2;

							D = expf(-slope_x*slope_x - slope_y*slope_y) / (M_PI_F * alpha2 * cosThetaM4);

							/* G1(i,m) */
							G1i = bsdf_beckmann_aniso_G1(alpha_x, alpha_y, dot(*omega_in, N), dot(*omega_in, X), dot(*omega_in, Y));
						}

						float G = G1o * G1i;

						/* see eval function for derivation */
						float common = D * 0.25f / cosNO;
						float out = G * common;
						*pdf = G1o * common;

						*eval = make_float3(out, out, out);
					}

#ifdef __RAY_DIFFERENTIALS__
					*domega_in_dx = (2 * dot(m, dIdx)) * m - dIdx;
					*domega_in_dy = (2 * dot(m, dIdy)) * m - dIdy;
#endif
				}
			}
		}
		else {
			/* CAUTION: the i and o variables are inverted relative to the paper
			 * eq. 39 - compute actual refractive direction */
			float3 R, T;
#ifdef __RAY_DIFFERENTIALS__
			float3 dRdx, dRdy, dTdx, dTdy;
#endif
			float m_eta = bsdf->ior, fresnel;
			bool inside;

			fresnel = fresnel_dielectric(m_eta, m, I, &R, &T,
#ifdef __RAY_DIFFERENTIALS__
				dIdx, dIdy, &dRdx, &dRdy, &dTdx, &dTdy,
#endif
				&inside);

			if(!inside && fresnel != 1.0f) {
				*omega_in = T;

#ifdef __RAY_DIFFERENTIALS__
				*domega_in_dx = dTdx;
				*domega_in_dy = dTdy;
#endif

				if(alpha_x*alpha_y <= 1e-7f || fabsf(m_eta - 1.0f) < 1e-4f) {
					/* some high number for MIS */
					*pdf = 1e6f;
					*eval = make_float3(1e6f, 1e6f, 1e6f);
				}
				else {
					/* eq. 33 */
					float alpha2 = alpha_x * alpha_y;
					float cosThetaM2 = cosThetaM * cosThetaM;
					float cosThetaM4 = cosThetaM2 * cosThetaM2;
					float tanThetaM2 = 1/(cosThetaM2) - 1;
					float D = expf(-tanThetaM2 / alpha2) / (M_PI_F * alpha2 *  cosThetaM4);

					/* eval BRDF*cosNI */
					float cosNI = dot(N, *omega_in);

					/* eq. 26, 27: now calculate G1(i,m) */
					float G1i = bsdf_beckmann_G1(alpha_x, cosNI);
					float G = G1o * G1i;

					/* eq. 21 */
					float cosHI = dot(m, *omega_in);
					float cosHO = dot(m, I);
					float Ht2 = m_eta * cosHI + cosHO;
					Ht2 *= Ht2;

					/* see eval function for derivation */
					float common = D * (m_eta * m_eta) / (cosNO * Ht2);
					float out = G * fabsf(cosHI * cosHO) * common;
					*pdf = G1o * cosHO * fabsf(cosHI) * common;

					*eval = make_float3(out, out, out);
				}
			}
		}
	}
	return (m_refractive) ? LABEL_TRANSMIT|LABEL_GLOSSY : LABEL_REFLECT|LABEL_GLOSSY;
}

CCL_NAMESPACE_END

#endif /* __BSDF_MICROFACET_H__ */

