Cycles: Ashikhmin-Shirley anisotropic BSDF

* Ashikhmin-Shirley anisotropic BSDF was added as closure
* Anisotropic BSDF node now has two distributions

Reviewers: brecht, dingto

Differential Revision: https://developer.blender.org/D549

2 files changed, 210 insertions, 0 deletions

diff --git a/intern/cycles/kernel/closure/bsdf.h b/intern/cycles/kernel/closure/bsdf.h
index 24b54cd9d9e..371d0bfa8ea 100644
--- a/intern/cycles/kernel/closure/bsdf.h
+++ b/intern/cycles/kernel/closure/bsdf.h
@@ -25,6 +25,7 @@
 #include "../closure/bsdf_transparent.h"
 #ifdef __ANISOTROPIC__
 #include "../closure/bsdf_ward.h"
+#include "../closure/bsdf_ashikhmin_shirley.h"
 #endif
 #include "../closure/bsdf_westin.h"
 #include "../closure/bsdf_toon.h"
@@ -97,6 +98,10 @@ ccl_device int bsdf_sample(KernelGlobals *kg, const ShaderData *sd, const Shader
 			label = bsdf_ward_sample(sc, sd->Ng, sd->I, sd->dI.dx, sd->dI.dy, randu, randv,
 				eval, omega_in, &domega_in->dx, &domega_in->dy, pdf);
 			break;
+		case CLOSURE_BSDF_ASHIKHMIN_SHIRLEY_ID:
+			label = bsdf_ashikhmin_shirley_sample(sc, sd->Ng, sd->I, sd->dI.dx, sd->dI.dy, randu, randv,
+				eval, omega_in, &domega_in->dx, &domega_in->dy, pdf);
+			break;
 #endif
 		case CLOSURE_BSDF_ASHIKHMIN_VELVET_ID:
 			label = bsdf_ashikhmin_velvet_sample(sc, sd->Ng, sd->I, sd->dI.dx, sd->dI.dy, randu, randv,
@@ -189,6 +194,9 @@ ccl_device float3 bsdf_eval(KernelGlobals *kg, const ShaderData *sd, const Shade
 			case CLOSURE_BSDF_WARD_ID:
 				eval = bsdf_ward_eval_reflect(sc, sd->I, omega_in, pdf);
 				break;
+			case CLOSURE_BSDF_ASHIKHMIN_SHIRLEY_ID:
+				eval = bsdf_ashikhmin_shirley_eval_reflect(sc, sd->I, omega_in, pdf);
+				break;
 #endif
 			case CLOSURE_BSDF_ASHIKHMIN_VELVET_ID:
 				eval = bsdf_ashikhmin_velvet_eval_reflect(sc, sd->I, omega_in, pdf);
@@ -256,6 +264,9 @@ ccl_device float3 bsdf_eval(KernelGlobals *kg, const ShaderData *sd, const Shade
 			case CLOSURE_BSDF_WARD_ID:
 				eval = bsdf_ward_eval_transmit(sc, sd->I, omega_in, pdf);
 				break;
+			case CLOSURE_BSDF_ASHIKHMIN_SHIRLEY_ID:
+				eval = bsdf_ashikhmin_shirley_eval_transmit(sc, sd->I, omega_in, pdf);
+				break;
 #endif
 			case CLOSURE_BSDF_ASHIKHMIN_VELVET_ID:
 				eval = bsdf_ashikhmin_velvet_eval_transmit(sc, sd->I, omega_in, pdf);
@@ -341,6 +352,9 @@ ccl_device void bsdf_blur(KernelGlobals *kg, ShaderClosure *sc, float roughness)
 		case CLOSURE_BSDF_WARD_ID:
 			bsdf_ward_blur(sc, roughness);
 			break;
+		case CLOSURE_BSDF_ASHIKHMIN_SHIRLEY_ID:
+			bsdf_ashikhmin_shirley_blur(sc, roughness);
+			break;
 #endif
 		case CLOSURE_BSDF_ASHIKHMIN_VELVET_ID:
 			bsdf_ashikhmin_velvet_blur(sc, roughness);
diff --git a/intern/cycles/kernel/closure/bsdf_ashikhmin_shirley.h b/intern/cycles/kernel/closure/bsdf_ashikhmin_shirley.h
new file mode 100644
index 00000000000..ea5b610ae56
--- /dev/null
+++ b/intern/cycles/kernel/closure/bsdf_ashikhmin_shirley.h
@@ -0,0 +1,196 @@
+/*
+ * Copyright 2011-2013 Blender Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License
+ */
+
+#ifndef __BSDF_ASHIKHMIN_SHIRLEY_H__
+#define __BSDF_ASHIKHMIN_SHIRLEY_H__
+
+/*
+ASHIKHMIN SHIRLEY BSDF
+
+Implementation of
+Michael Ashikhmin and Peter Shirley: "An Anisotropic Phong BRDF Model" (2000)
+
+The Fresnel factor is missing to get a separable bsdf (intensity*color), as is
+the case with all other microfacet-based BSDF implementations in Cycles.
+
+Other than that, the implementation directly follows the paper.
+*/
+
+CCL_NAMESPACE_BEGIN
+
+
+ccl_device int bsdf_ashikhmin_shirley_setup(ShaderClosure *sc)
+{
+	sc->data0 = clamp(sc->data0, 1e-4f, 1.0f); /* store roughness. could already convert to exponent to save some cycles in eval, */
+	sc->data1 = clamp(sc->data1, 1e-4f, 1.0f); /* but this is more consistent with other bsdfs and shader_blur. */
+
+	sc->type = CLOSURE_BSDF_ASHIKHMIN_SHIRLEY_ID;
+	return SD_BSDF | SD_BSDF_HAS_EVAL | SD_BSDF_GLOSSY;
+}
+
+ccl_device void bsdf_ashikhmin_shirley_blur(ShaderClosure *sc, float roughness)
+{
+	sc->data0 = fmaxf(roughness, sc->data0); /* clamp roughness */
+	sc->data1 = fmaxf(roughness, sc->data1);
+}
+
+ccl_device_inline float bsdf_ashikhmin_shirley_roughness_to_exponent(float roughness)
+{
+	return 2.0f / (roughness*roughness) - 2.0f;
+}
+
+ccl_device float3 bsdf_ashikhmin_shirley_eval_reflect(const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
+{
+	float3 N = sc->N;
+	float3 T = sc->T;
+
+	float NdotI = dot(N, I);           /* in Cycles/OSL convention I is omega_out    */
+	float NdotO = dot(N, omega_in);    /* and consequently we use for O omaga_in ;)  */
+
+	float out = 0.0f;
+
+	if (NdotI > 0.0f && NdotO > 0.0f) {
+		NdotI = fmaxf(NdotI, 1e-6f);
+		NdotO = fmaxf(NdotO, 1e-6f);
+		float3 H = normalize(omega_in + I);
+		float HdotI = fmaxf(dot(H, I), 1e-6f);
+		float HdotN = fmaxf(dot(H, N), 1e-6f);
+
+		float pump = 1.0f / fmaxf(1e-6f, (HdotI*fmaxf(NdotO, NdotI))); /* pump from original paper (first derivative disc., but cancels the HdotI in the pdf nicely) */
+		/*float pump = 1.0f / fmaxf(1e-4f, ((NdotO + NdotI) * (NdotO*NdotI))); */ /* pump from d-brdf paper */
+
+		float n_x = bsdf_ashikhmin_shirley_roughness_to_exponent(sc->data0);
+		float n_y = bsdf_ashikhmin_shirley_roughness_to_exponent(sc->data1);
+
+		if (n_x == n_y) {  /* => isotropic case */
+			float e = n_x;
+			float lobe = powf(HdotN, e);
+			float norm = (n_x + 1.0f) / (8.0f * M_PI_F);
+
+			out = NdotO * norm * lobe * pump;
+			*pdf = norm * lobe / HdotI; /* this is p_h / 4(H.I)  (conversion from 'wh measure' to 'wi measure', eq. 8 in paper) */
+		}
+		else {             /* => ANisotropic case */
+			float3 X, Y;
+			make_orthonormals_tangent(N, T, &X, &Y);
+
+			float HdotX = dot(H, X);
+			float HdotY = dot(H, Y);
+			float e = (n_x * HdotX*HdotX + n_y * HdotY*HdotY) / (1.0f - HdotN*HdotN);
+			float lobe = powf(HdotN, e);
+			float norm = sqrtf((n_x + 1.0f)*(n_y + 1.0f)) / (8.0f * M_PI_F);
+			
+			out = NdotO * norm * lobe * pump;
+			*pdf = norm * lobe / HdotI;
+		}
+	}
+
+	return make_float3(out, out, out);
+}
+
+ccl_device float3 bsdf_ashikhmin_shirley_eval_transmit(const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
+{
+	return make_float3(0.0f, 0.0f, 0.0f);
+}
+
+ccl_device_inline void bsdf_ashikhmin_shirley_sample_first_quadrant(float n_x, float n_y, float randu, float randv, float *phi, float *cos_theta)
+{
+	*phi = atanf(sqrtf((n_x + 1.0f) / (n_y + 1.0f)) * tanf(M_PI_2_F * randu));
+	float cos_phi = cosf(*phi);
+	float sin_phi = sinf(*phi);
+	*cos_theta = powf(randv, 1.0f / (n_x * cos_phi*cos_phi + n_y * sin_phi*sin_phi + 1.0f));
+}
+
+ccl_device int bsdf_ashikhmin_shirley_sample(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)
+{
+	float3 N = sc->N;
+	float3 T = sc->T;
+
+	float NdotI = dot(N, I);
+	if (NdotI > 0.0f) {
+
+		float n_x = bsdf_ashikhmin_shirley_roughness_to_exponent(sc->data0);
+		float n_y = bsdf_ashikhmin_shirley_roughness_to_exponent(sc->data1);
+
+		/* get x,y basis on the surface for anisotropy */
+		float3 X, Y;
+		make_orthonormals_tangent(N, T, &X, &Y);
+
+		/* sample spherical coords for h in tangent space */
+		float phi;
+		float cos_theta;
+		if (n_x == n_y) {  /* => simple isotropic sampling */
+			phi = M_2PI_F * randu;
+			cos_theta = powf(randv, 1.0f / (n_x + 1.0f));
+		}
+		else {             /* => more complex anisotropic sampling */
+			if (randu < 0.25f) {      /* first quadrant */
+				float remapped_randu = 4.0f * randu;
+				bsdf_ashikhmin_shirley_sample_first_quadrant(n_x, n_y, remapped_randu, randv, &phi, &cos_theta);
+			}
+			else if (randu < 0.5f) {  /* second quadrant */
+				float remapped_randu = 4.0f * (.5f - randu);
+				bsdf_ashikhmin_shirley_sample_first_quadrant(n_x, n_y, remapped_randu, randv, &phi, &cos_theta);
+				phi = M_PI_F - phi;
+			}
+			else if (randu < 0.75f) { /* third quadrant */
+				float remapped_randu = 4.0f * (randu - 0.5f);
+				bsdf_ashikhmin_shirley_sample_first_quadrant(n_x, n_y, remapped_randu, randv, &phi, &cos_theta);
+				phi = M_PI_F + phi;
+			}
+			else {                   /* fourth quadrant */
+				float remapped_randu = 4.0f * (1.0f - randu);
+				bsdf_ashikhmin_shirley_sample_first_quadrant(n_x, n_y, remapped_randu, randv, &phi, &cos_theta);
+				phi = 2.0f * M_PI_F - phi;
+			}
+		}
+
+		/* get half vector in tangent space */
+		float sin_theta = sqrtf(fmaxf(0.0f, 1.0f - cos_theta*cos_theta));
+		float cos_phi = cosf(phi);
+		float sin_phi = sinf(phi); /* no sqrt(1-cos^2) here b/c it causes artifacts */
+		float3 h = make_float3(
+			sin_theta * cos_phi,
+			sin_theta * sin_phi,
+			cos_theta
+			);
+
+		/* half vector to world space */
+		float3 H = h.x*X + h.y*Y + h.z*N;
+		float HdotI = dot(H, I);
+		if (HdotI < 0.0f) H = -H;
+
+		/* reflect I on H to get omega_in */
+		*omega_in = -I + (2.0f * HdotI) * H;
+
+		/* leave the rest to eval_reflect */
+		/* (could maybe optimize a few things by manual inlining, but I doubt it would make much difference) */
+		*eval = bsdf_ashikhmin_shirley_eval_reflect(sc, I, *omega_in, pdf);
+
+#ifdef __RAY_DIFFERENTIALS__
+		/* just do the reflection thing for now */
+		*domega_in_dx = (2.0f * dot(N, dIdx)) * N - dIdx;
+		*domega_in_dy = (2.0f * dot(N, dIdy)) * N - dIdy;
+#endif
+	}
+
+	return LABEL_REFLECT | LABEL_GLOSSY;
+}
+
+
+CCL_NAMESPACE_END
+
+#endif /* __BSDF_ASHIKHMIN_SHIRLEY_H__ */