1 files changed, 25 insertions, 15 deletions

diff --git a/intern/cycles/kernel/closure/volume.h b/intern/cycles/kernel/closure/volume.h
index 4bb5e680723..da791e9aa73 100644
--- a/intern/cycles/kernel/closure/volume.h
+++ b/intern/cycles/kernel/closure/volume.h
@@ -83,35 +83,45 @@ ccl_device float3 volume_henyey_greenstein_eval_phase(const ShaderClosure *sc, c
 	return make_float3(*pdf, *pdf, *pdf);
 }
 
-ccl_device int volume_henyey_greenstein_sample(const ShaderClosure *sc, 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)
+ccl_device float3 henyey_greenstrein_sample(float3 D, float g, float randu, float randv, float *pdf)
 {
-	const HenyeyGreensteinVolume *volume = (const HenyeyGreensteinVolume*)sc;
-	float g = volume->g;
-	float cos_phi, sin_phi, cos_theta;
-
 	/* match pdf for small g */
-	if(fabsf(g) < 1e-3f) {
+	float cos_theta;
+	bool isotropic = fabsf(g) < 1e-3f;
+
+	if(isotropic) {
 		cos_theta = (1.0f - 2.0f * randu);
-		*pdf = M_1_PI_F * 0.25f;
+		if(pdf) {
+			*pdf = M_1_PI_F * 0.25f;
+		}
 	}
 	else {
 		float k = (1.0f - g * g) / (1.0f - g + 2.0f * g * randu);
 		cos_theta = (1.0f + g * g - k * k) / (2.0f * g);
-		*pdf = single_peaked_henyey_greenstein(cos_theta, g);
+		if(pdf) {
+			*pdf = single_peaked_henyey_greenstein(cos_theta, g);
+		}
 	}
 
 	float sin_theta = safe_sqrtf(1.0f - cos_theta * cos_theta);
-
 	float phi = M_2PI_F * randv;
-	cos_phi = cosf(phi);
-	sin_phi = sinf(phi);
+	float3 dir = make_float3(sin_theta * cosf(phi), sin_theta * sinf(phi), cos_theta);
 
-	/* note that I points towards the viewer and so is used negated */
 	float3 T, B;
-	make_orthonormals(-I, &T, &B);
-	*omega_in = sin_theta * cos_phi * T + sin_theta * sin_phi * B + cos_theta * (-I);
+	make_orthonormals(D, &T, &B);
+	dir = dir.x * T + dir.y * B + dir.z * D;
+
+	return dir;
+}
+
+ccl_device int volume_henyey_greenstein_sample(const ShaderClosure *sc, 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 HenyeyGreensteinVolume *volume = (const HenyeyGreensteinVolume*)sc;
+	float g = volume->g;
 
+	/* note that I points towards the viewer and so is used negated */
+	*omega_in = henyey_greenstrein_sample(-I, g, randu, randv, pdf);
 	*eval = make_float3(*pdf, *pdf, *pdf); /* perfect importance sampling */
 
 #ifdef __RAY_DIFFERENTIALS__