Merge branch 'master' into blender2.8

23 files changed, 310 insertions, 409 deletions

diff --git a/intern/cycles/blender/blender_mesh.cpp b/intern/cycles/blender/blender_mesh.cpp
index 20f0fb04c89..19f4d19179d 100644
--- a/intern/cycles/blender/blender_mesh.cpp
+++ b/intern/cycles/blender/blender_mesh.cpp
@@ -63,9 +63,8 @@ inline void face_split_tri_indices(const int face_flag,
 		tri_b[1] = 3;
 		tri_b[2] = 1;
 	}
-	else /*if(face_flag & FACE_FLAG_DIVIDE_13)*/ {
-		assert(face_flag & FACE_FLAG_DIVIDE_13);
-
+	else {
+		/* Quad with FACE_FLAG_DIVIDE_13 or single triangle. */
 		tri_a[0] = 0;
 		tri_a[1] = 1;
 		tri_a[2] = 2;
diff --git a/intern/cycles/kernel/closure/bssrdf.h b/intern/cycles/kernel/closure/bssrdf.h
index 06221189060..267aeea6e86 100644
--- a/intern/cycles/kernel/closure/bssrdf.h
+++ b/intern/cycles/kernel/closure/bssrdf.h
@@ -400,7 +400,7 @@ ccl_device int bssrdf_setup(Bssrdf *bssrdf, ClosureType type)
 			bssrdf_burley_setup(bssrdf);
 		}
 
-		return SD_BSDF|SD_BSDF_HAS_EVAL|SD_BSSRDF;
+		return SD_BSSRDF;
 	}
 }
 
diff --git a/intern/cycles/kernel/kernel_bake.h b/intern/cycles/kernel/kernel_bake.h
index b05f6e9ed5e..f06005c5072 100644
--- a/intern/cycles/kernel/kernel_bake.h
+++ b/intern/cycles/kernel/kernel_bake.h
@@ -51,8 +51,7 @@ ccl_device_inline void compute_light_pass(KernelGlobals *kg,
 	path_state_init(kg, &emission_sd, &state, rng_hash, sample, NULL);
 
 	/* evaluate surface shader */
-	float rbsdf = path_state_rng_1D(kg, &state, PRNG_BSDF);
-	shader_eval_surface(kg, sd, &state, rbsdf, state.flag);
+	shader_eval_surface(kg, sd, &state, state.flag);
 
 	/* TODO, disable more closures we don't need besides transparent */
 	shader_bsdf_disable_transparency(kg, sd);
@@ -241,12 +240,12 @@ ccl_device float3 kernel_bake_evaluate_direct_indirect(KernelGlobals *kg,
 		}
 		else {
 			/* surface color of the pass only */
-			shader_eval_surface(kg, sd, state, 0.0f, 0);
+			shader_eval_surface(kg, sd, state, 0);
 			return kernel_bake_shader_bsdf(kg, sd, type);
 		}
 	}
 	else {
-		shader_eval_surface(kg, sd, state, 0.0f, 0);
+		shader_eval_surface(kg, sd, state, 0);
 		color = kernel_bake_shader_bsdf(kg, sd, type);
 	}
 
@@ -338,7 +337,7 @@ ccl_device void kernel_bake_evaluate(KernelGlobals *kg, ccl_global uint4 *input,
 		case SHADER_EVAL_NORMAL:
 		{
 			if((sd.flag & SD_HAS_BUMP)) {
-				shader_eval_surface(kg, &sd, &state, 0.f, 0);
+				shader_eval_surface(kg, &sd, &state, 0);
 			}
 
 			/* encoding: normal = (2 * color) - 1 */
@@ -352,7 +351,7 @@ ccl_device void kernel_bake_evaluate(KernelGlobals *kg, ccl_global uint4 *input,
 		}
 		case SHADER_EVAL_EMISSION:
 		{
-			shader_eval_surface(kg, &sd, &state, 0.f, 0);
+			shader_eval_surface(kg, &sd, &state, 0);
 			out = shader_emissive_eval(kg, &sd);
 			break;
 		}
diff --git a/intern/cycles/kernel/kernel_emission.h b/intern/cycles/kernel/kernel_emission.h
index 13d4759a9ec..45b8c6311e1 100644
--- a/intern/cycles/kernel/kernel_emission.h
+++ b/intern/cycles/kernel/kernel_emission.h
@@ -70,7 +70,7 @@ ccl_device_noinline float3 direct_emissive_eval(KernelGlobals *kg,
 		/* no path flag, we're evaluating this for all closures. that's weak but
 		 * we'd have to do multiple evaluations otherwise */
 		path_state_modify_bounce(state, true);
-		shader_eval_surface(kg, emission_sd, state, 0.0f, 0);
+		shader_eval_surface(kg, emission_sd, state, 0);
 		path_state_modify_bounce(state, false);
 
 		/* evaluate emissive closure */
diff --git a/intern/cycles/kernel/kernel_path.h b/intern/cycles/kernel/kernel_path.h
index 3a242a06a72..d43d6374c13 100644
--- a/intern/cycles/kernel/kernel_path.h
+++ b/intern/cycles/kernel/kernel_path.h
@@ -210,8 +210,8 @@ ccl_device_forceinline VolumeIntegrateResult kernel_path_volume(
 				/* indirect sample. if we use distance sampling and take just
 				 * one sample for direct and indirect light, we could share
 				 * this computation, but makes code a bit complex */
-				float rphase = path_state_rng_1D_for_decision(kg, state, PRNG_PHASE);
-				float rscatter = path_state_rng_1D_for_decision(kg, state, PRNG_SCATTER_DISTANCE);
+				float rphase = path_state_rng_1D(kg, state, PRNG_PHASE_CHANNEL);
+				float rscatter = path_state_rng_1D(kg, state, PRNG_SCATTER_DISTANCE);
 
 				result = kernel_volume_decoupled_scatter(kg,
 					state, &volume_ray, sd, throughput,
@@ -434,11 +434,8 @@ ccl_device void kernel_path_indirect(KernelGlobals *kg,
 		                      sd,
 		                      &isect,
 		                      ray);
-		float rbsdf = path_state_rng_1D_for_decision(kg, state, PRNG_BSDF);
-		shader_eval_surface(kg, sd, state, rbsdf, state->flag);
-#ifdef __BRANCHED_PATH__
-		shader_merge_closures(sd);
-#endif  /* __BRANCHED_PATH__ */
+		shader_eval_surface(kg, sd, state, state->flag);
+		shader_prepare_closures(sd, state);
 
 		/* Apply shadow catcher, holdout, emission. */
 		if(!kernel_path_shader_apply(kg,
@@ -462,7 +459,7 @@ ccl_device void kernel_path_indirect(KernelGlobals *kg,
 			break;
 		}
 		else if(probability != 1.0f) {
-			float terminate = path_state_rng_1D_for_decision(kg, state, PRNG_TERMINATE);
+			float terminate = path_state_rng_1D(kg, state, PRNG_TERMINATE);
 
 			if(terminate >= probability)
 				break;
@@ -483,21 +480,18 @@ ccl_device void kernel_path_indirect(KernelGlobals *kg,
 		/* bssrdf scatter to a different location on the same object, replacing
 		 * the closures with a diffuse BSDF */
 		if(sd->flag & SD_BSSRDF) {
-			float bssrdf_probability;
-			ShaderClosure *sc = subsurface_scatter_pick_closure(kg, sd, &bssrdf_probability);
+			float bssrdf_u, bssrdf_v;
+			path_state_rng_2D(kg,
+			                  state,
+			                  PRNG_BSDF_U,
+			                  &bssrdf_u, &bssrdf_v);
 
-			/* modify throughput for picking bssrdf or bsdf */
-			throughput *= bssrdf_probability;
+			const ShaderClosure *sc = shader_bssrdf_pick(sd, &throughput, &bssrdf_u);
 
 			/* do bssrdf scatter step if we picked a bssrdf closure */
 			if(sc) {
 				uint lcg_state = lcg_state_init(state, 0x68bc21eb);
 
-				float bssrdf_u, bssrdf_v;
-				path_state_rng_2D(kg,
-				                  state,
-				                  PRNG_BSDF_U,
-				                  &bssrdf_u, &bssrdf_v);
 				subsurface_scatter_step(kg,
 				                        sd,
 				                        state,
@@ -591,8 +585,8 @@ ccl_device_forceinline void kernel_path_integrate(
 
 		/* Setup and evaluate shader. */
 		shader_setup_from_ray(kg, &sd, &isect, ray);
-		float rbsdf = path_state_rng_1D_for_decision(kg, state, PRNG_BSDF);
-		shader_eval_surface(kg, &sd, state, rbsdf, state->flag);
+		shader_eval_surface(kg, &sd, state, state->flag);
+		shader_prepare_closures(&sd, state);
 
 		/* Apply shadow catcher, holdout, emission. */
 		if(!kernel_path_shader_apply(kg,
@@ -616,7 +610,7 @@ ccl_device_forceinline void kernel_path_integrate(
 			break;
 		}
 		else if(probability != 1.0f) {
-			float terminate = path_state_rng_1D_for_decision(kg, state, PRNG_TERMINATE);
+			float terminate = path_state_rng_1D(kg, state, PRNG_TERMINATE);
 			if(terminate >= probability)
 				break;
 
diff --git a/intern/cycles/kernel/kernel_path_branched.h b/intern/cycles/kernel/kernel_path_branched.h
index 3994d8d4954..010988d2a02 100644
--- a/intern/cycles/kernel/kernel_path_branched.h
+++ b/intern/cycles/kernel/kernel_path_branched.h
@@ -339,8 +339,8 @@ ccl_device void kernel_branched_path_integrate(KernelGlobals *kg,
 					/* scatter sample. if we use distance sampling and take just one
 					 * sample for direct and indirect light, we could share this
 					 * computation, but makes code a bit complex */
-					float rphase = path_state_rng_1D_for_decision(kg, &ps, PRNG_PHASE);
-					float rscatter = path_state_rng_1D_for_decision(kg, &ps, PRNG_SCATTER_DISTANCE);
+					float rphase = path_state_rng_1D(kg, &ps, PRNG_PHASE_CHANNEL);
+					float rscatter = path_state_rng_1D(kg, &ps, PRNG_SCATTER_DISTANCE);
 
 					VolumeIntegrateResult result = kernel_volume_decoupled_scatter(kg,
 						&ps, &pray, &sd, &tp, rphase, rscatter, &volume_segment, NULL, false);
@@ -439,7 +439,7 @@ ccl_device void kernel_branched_path_integrate(KernelGlobals *kg,
 
 		/* Setup and evaluate shader. */
 		shader_setup_from_ray(kg, &sd, &isect, &ray);
-		shader_eval_surface(kg, &sd, &state, 0.0f, state.flag);
+		shader_eval_surface(kg, &sd, &state, state.flag);
 		shader_merge_closures(&sd);
 
 		/* Apply shadow catcher, holdout, emission. */
@@ -466,7 +466,7 @@ ccl_device void kernel_branched_path_integrate(KernelGlobals *kg,
 				break;
 			}
 			else if(probability != 1.0f) {
-				float terminate = path_state_rng_1D_for_decision(kg, &state, PRNG_TERMINATE);
+				float terminate = path_state_rng_1D(kg, &state, PRNG_TERMINATE);
 
 				if(terminate >= probability)
 					break;
diff --git a/intern/cycles/kernel/kernel_path_state.h b/intern/cycles/kernel/kernel_path_state.h
index bb09b4ac080..eccee54c0e3 100644
--- a/intern/cycles/kernel/kernel_path_state.h
+++ b/intern/cycles/kernel/kernel_path_state.h
@@ -76,12 +76,12 @@ ccl_device_inline void path_state_next(KernelGlobals *kg, ccl_addr_space PathSta
 		state->flag |= PATH_RAY_TRANSPARENT;
 		state->transparent_bounce++;
 
-		/* don't increase random number generator offset here, to avoid some
-		 * unwanted patterns, see path_state_rng_1D_for_decision */
-
 		if(!kernel_data.integrator.transparent_shadows)
 			state->flag |= PATH_RAY_MIS_SKIP;
 
+		/* random number generator next bounce */
+		state->rng_offset += PRNG_BOUNCE_NUM;
+
 		return;
 	}
 
diff --git a/intern/cycles/kernel/kernel_path_subsurface.h b/intern/cycles/kernel/kernel_path_subsurface.h
index 619d57e71fb..1753618607a 100644
--- a/intern/cycles/kernel/kernel_path_subsurface.h
+++ b/intern/cycles/kernel/kernel_path_subsurface.h
@@ -32,11 +32,10 @@ bool kernel_path_subsurface_scatter(
         ccl_addr_space float3 *throughput,
         ccl_addr_space SubsurfaceIndirectRays *ss_indirect)
 {
-	float bssrdf_probability;
-	ShaderClosure *sc = subsurface_scatter_pick_closure(kg, sd, &bssrdf_probability);
+	float bssrdf_u, bssrdf_v;
+	path_state_rng_2D(kg, state, PRNG_BSDF_U, &bssrdf_u, &bssrdf_v);
 
-	/* modify throughput for picking bssrdf or bsdf */
-	*throughput *= bssrdf_probability;
+	const ShaderClosure *sc = shader_bssrdf_pick(sd, throughput, &bssrdf_u);
 
 	/* do bssrdf scatter step if we picked a bssrdf closure */
 	if(sc) {
@@ -49,8 +48,6 @@ bool kernel_path_subsurface_scatter(
 		uint lcg_state = lcg_state_init_addrspace(state, 0x68bc21eb);
 
 		SubsurfaceIntersection ss_isect;
-		float bssrdf_u, bssrdf_v;
-		path_state_rng_2D(kg, state, PRNG_BSDF_U, &bssrdf_u, &bssrdf_v);
 		int num_hits = subsurface_scatter_multi_intersect(kg,
 		                                                  &ss_isect,
 		                                                  sd,
diff --git a/intern/cycles/kernel/kernel_path_volume.h b/intern/cycles/kernel/kernel_path_volume.h
index e7e24f853c2..3cf897ac49c 100644
--- a/intern/cycles/kernel/kernel_path_volume.h
+++ b/intern/cycles/kernel/kernel_path_volume.h
@@ -77,7 +77,7 @@ bool kernel_path_volume_bounce(
 	float3 phase_omega_in;
 	differential3 phase_domega_in;
 	float phase_u, phase_v;
-	path_state_rng_2D(kg, state, PRNG_PHASE_U, &phase_u, &phase_v);
+	path_state_rng_2D(kg, state, PRNG_BSDF_U, &phase_u, &phase_v);
 	int label;
 
 	label = shader_volume_phase_sample(kg, sd, phase_u, phase_v, &phase_eval,
@@ -155,8 +155,8 @@ ccl_device void kernel_branched_path_volume_connect_light(
 				float3 tp = throughput;
 
 				/* sample position on volume segment */
-				float rphase = path_branched_rng_1D_for_decision(kg, state->rng_hash, state, j, num_samples, PRNG_PHASE);
-				float rscatter = path_branched_rng_1D_for_decision(kg, state->rng_hash, state, j, num_samples, PRNG_SCATTER_DISTANCE);
+				float rphase = path_branched_rng_1D(kg, state->rng_hash, state, j, num_samples, PRNG_PHASE_CHANNEL);
+				float rscatter = path_branched_rng_1D(kg, state->rng_hash, state, j, num_samples, PRNG_SCATTER_DISTANCE);
 
 				VolumeIntegrateResult result = kernel_volume_decoupled_scatter(kg,
 					state, ray, sd, &tp, rphase, rscatter, segment, (ls.t != FLT_MAX)? &ls.P: NULL, false);
@@ -201,8 +201,8 @@ ccl_device void kernel_branched_path_volume_connect_light(
 				float3 tp = throughput;
 
 				/* sample position on volume segment */
-				float rphase = path_branched_rng_1D_for_decision(kg, state->rng_hash, state, j, num_samples, PRNG_PHASE);
-				float rscatter = path_branched_rng_1D_for_decision(kg, state->rng_hash, state, j, num_samples, PRNG_SCATTER_DISTANCE);
+				float rphase = path_branched_rng_1D(kg, state->rng_hash, state, j, num_samples, PRNG_PHASE_CHANNEL);
+				float rscatter = path_branched_rng_1D(kg, state->rng_hash, state, j, num_samples, PRNG_SCATTER_DISTANCE);
 
 				VolumeIntegrateResult result = kernel_volume_decoupled_scatter(kg,
 					state, ray, sd, &tp, rphase, rscatter, segment, (ls.t != FLT_MAX)? &ls.P: NULL, false);
@@ -238,8 +238,8 @@ ccl_device void kernel_branched_path_volume_connect_light(
 		float3 tp = throughput;
 
 		/* sample position on volume segment */
-		float rphase = path_state_rng_1D_for_decision(kg, state, PRNG_PHASE);
-		float rscatter = path_state_rng_1D_for_decision(kg, state, PRNG_SCATTER_DISTANCE);
+		float rphase = path_state_rng_1D(kg, state, PRNG_PHASE_CHANNEL);
+		float rscatter = path_state_rng_1D(kg, state, PRNG_SCATTER_DISTANCE);
 
 		VolumeIntegrateResult result = kernel_volume_decoupled_scatter(kg,
 			state, ray, sd, &tp, rphase, rscatter, segment, (ls.t != FLT_MAX)? &ls.P: NULL, false);
diff --git a/intern/cycles/kernel/kernel_random.h b/intern/cycles/kernel/kernel_random.h
index b35ed3bd279..11798d87cb5 100644
--- a/intern/cycles/kernel/kernel_random.h
+++ b/intern/cycles/kernel/kernel_random.h
@@ -30,12 +30,6 @@ CCL_NAMESPACE_BEGIN
 
 #ifdef __SOBOL__
 
-/* Skip initial numbers that are not as well distributed, especially the
- * first sequence is just 0 everywhere, which can be problematic for e.g.
- * path termination.
- */
-#define SOBOL_SKIP 64
-
 ccl_device uint sobol_dimension(KernelGlobals *kg, int index, int dimension)
 {
 	uint result = 0;
@@ -73,7 +67,7 @@ ccl_device_forceinline float path_rng_1D(KernelGlobals *kg,
 
 #ifdef __SOBOL__
 	/* Sobol sequence value using direction vectors. */
-	uint result = sobol_dimension(kg, sample + SOBOL_SKIP, dimension);
+	uint result = sobol_dimension(kg, sample, dimension);
 	float r = (float)result * (1.0f/(float)0xFFFFFFFF);
 
 	/* Cranly-Patterson rotation using rng seed */
@@ -186,25 +180,6 @@ ccl_device_inline float path_state_rng_1D(KernelGlobals *kg,
 	                   state->rng_offset + dimension);
 }
 
-ccl_device_inline float path_state_rng_1D_for_decision(
-        KernelGlobals *kg,
-        const ccl_addr_space PathState *state,
-        int dimension)
-{
-	/* The rng_offset is not increased for transparent bounces. if we do then
-	 * fully transparent objects can become subtly visible by the different
-	 * sampling patterns used where the transparent object is.
-	 *
-	 * however for some random numbers that will determine if we next bounce
-	 * is transparent we do need to increase the offset to avoid always making
-	 * the same decision. */
-	const int rng_offset = state->rng_offset + state->transparent_bounce * PRNG_BOUNCE_NUM;
-	return path_rng_1D(kg,
-	                   state->rng_hash,
-	                   state->sample, state->num_samples,
-	                   rng_offset + dimension);
-}
-
 ccl_device_inline void path_state_rng_2D(KernelGlobals *kg,
                                          const ccl_addr_space PathState *state,
                                          int dimension,
@@ -232,22 +207,6 @@ ccl_device_inline float path_branched_rng_1D(
 	                   state->rng_offset + dimension);
 }
 
-ccl_device_inline float path_branched_rng_1D_for_decision(
-        KernelGlobals *kg,
-        uint rng_hash,
-        const ccl_addr_space PathState *state,
-        int branch,
-        int num_branches,
-        int dimension)
-{
-	const int rng_offset = state->rng_offset + state->transparent_bounce * PRNG_BOUNCE_NUM;
-	return path_rng_1D(kg,
-	                   rng_hash,
-	                   state->sample * num_branches + branch,
-	                   state->num_samples * num_branches,
-	                   rng_offset + dimension);
-}
-
 ccl_device_inline void path_branched_rng_2D(
         KernelGlobals *kg,
         uint rng_hash,
@@ -273,7 +232,7 @@ ccl_device_inline float path_state_rng_light_termination(
         const ccl_addr_space PathState *state)
 {
 	if(kernel_data.integrator.light_inv_rr_threshold > 0.0f) {
-		return path_state_rng_1D_for_decision(kg, state, PRNG_LIGHT_TERMINATE);
+		return path_state_rng_1D(kg, state, PRNG_LIGHT_TERMINATE);
 	}
 	return 0.0f;
 }
@@ -286,12 +245,12 @@ ccl_device_inline float path_branched_rng_light_termination(
         int num_branches)
 {
 	if(kernel_data.integrator.light_inv_rr_threshold > 0.0f) {
-		return path_branched_rng_1D_for_decision(kg,
-		                                         rng_hash,
-		                                         state,
-		                                         branch,
-		                                         num_branches,
-		                                         PRNG_LIGHT_TERMINATE);
+		return path_branched_rng_1D(kg,
+		                            rng_hash,
+		                            state,
+		                            branch,
+		                            num_branches,
+		                            PRNG_LIGHT_TERMINATE);
 	}
 	return 0.0f;
 }
diff --git a/intern/cycles/kernel/kernel_shader.h b/intern/cycles/kernel/kernel_shader.h
index 5964aca0c78..bb3add5d7ca 100644
--- a/intern/cycles/kernel/kernel_shader.h
+++ b/intern/cycles/kernel/kernel_shader.h
@@ -494,20 +494,45 @@ ccl_device_inline void shader_merge_closures(ShaderData *sd)
 }
 #endif
 
+/* Defensive sampling. */
+
+ccl_device_inline void shader_prepare_closures(ShaderData *sd,
+                                               ccl_addr_space PathState *state)
+{
+	/* We can likely also do defensive sampling at deeper bounces, particularly
+	 * for cases like a perfect mirror but possibly also others. This will need
+	 * a good heuristic. */
+	if(state->bounce + state->transparent_bounce == 0 && sd->num_closure > 1) {
+		float sum = 0.0f;
+
+		for(int i = 0; i < sd->num_closure; i++) {
+			ShaderClosure *sc = &sd->closure[i];
+			if(CLOSURE_IS_BSDF_OR_BSSRDF(sc->type)) {
+				sum += sc->sample_weight;
+			}
+		}
+
+		for(int i = 0; i < sd->num_closure; i++) {
+			ShaderClosure *sc = &sd->closure[i];
+			if(CLOSURE_IS_BSDF_OR_BSSRDF(sc->type)) {
+				sc->sample_weight = max(sc->sample_weight, 0.125f * sum);
+			}
+		}
+	}
+}
+
+
 /* BSDF */
 
 ccl_device_inline void _shader_bsdf_multi_eval(KernelGlobals *kg, ShaderData *sd, const float3 omega_in, float *pdf,
-	int skip_bsdf, BsdfEval *result_eval, float sum_pdf, float sum_sample_weight)
+	const ShaderClosure *skip_sc, BsdfEval *result_eval, float sum_pdf, float sum_sample_weight)
 {
 	/* this is the veach one-sample model with balance heuristic, some pdf
 	 * factors drop out when using balance heuristic weighting */
 	for(int i = 0; i < sd->num_closure; i++) {
-		if(i == skip_bsdf)
-			continue;
-
 		const ShaderClosure *sc = &sd->closure[i];
 
-		if(CLOSURE_IS_BSDF(sc->type)) {
+		if(sc != skip_sc && CLOSURE_IS_BSDF(sc->type)) {
 			float bsdf_pdf = 0.0f;
 			float3 eval = bsdf_eval(kg, sd, sc, omega_in, &bsdf_pdf);
 
@@ -570,7 +595,7 @@ void shader_bsdf_eval(KernelGlobals *kg,
 #endif
 	{
 		float pdf;
-		_shader_bsdf_multi_eval(kg, sd, omega_in, &pdf, -1, eval, 0.0f, 0.0f);
+		_shader_bsdf_multi_eval(kg, sd, omega_in, &pdf, NULL, eval, 0.0f, 0.0f);
 		if(use_mis) {
 			float weight = power_heuristic(light_pdf, pdf);
 			bsdf_eval_mis(eval, weight);
@@ -578,48 +603,120 @@ void shader_bsdf_eval(KernelGlobals *kg,
 	}
 }
 
-ccl_device_inline int shader_bsdf_sample(KernelGlobals *kg,
-                                         ShaderData *sd,
-                                         float randu, float randv,
-                                         BsdfEval *bsdf_eval,
-                                         float3 *omega_in,
-                                         differential3 *domega_in,
-                                         float *pdf)
+ccl_device_inline const ShaderClosure *shader_bsdf_pick(ShaderData *sd,
+                                                        float *randu)
 {
 	int sampled = 0;
 
 	if(sd->num_closure > 1) {
-		/* pick a BSDF closure based on sample weights */
+		/* Pick a BSDF or based on sample weights. */
 		float sum = 0.0f;
 
-		for(sampled = 0; sampled < sd->num_closure; sampled++) {
-			const ShaderClosure *sc = &sd->closure[sampled];
-			
-			if(CLOSURE_IS_BSDF(sc->type))
+		for(int i = 0; i < sd->num_closure; i++) {
+			const ShaderClosure *sc = &sd->closure[i];
+
+			if(CLOSURE_IS_BSDF(sc->type)) {
 				sum += sc->sample_weight;
+			}
 		}
 
-		float r = sd->randb_closure*sum;
-		sum = 0.0f;
+		float r = (*randu)*sum;
+		float partial_sum = 0.0f;
+
+		for(int i = 0; i < sd->num_closure; i++) {
+			const ShaderClosure *sc = &sd->closure[i];
 
-		for(sampled = 0; sampled < sd->num_closure; sampled++) {
-			const ShaderClosure *sc = &sd->closure[sampled];
-			
 			if(CLOSURE_IS_BSDF(sc->type)) {
-				sum += sc->sample_weight;
+				float next_sum = partial_sum + sc->sample_weight;
+
+				if(r < next_sum) {
+					sampled = i;
 
-				if(r <= sum)
+					/* Rescale to reuse for direction sample, to better
+					 * preserve stratifaction. */
+					*randu = (r - partial_sum) / sc->sample_weight;
 					break;
+				}
+
+				partial_sum = next_sum;
 			}
 		}
+	}
 
-		if(sampled == sd->num_closure) {
-			*pdf = 0.0f;
-			return LABEL_NONE;
+	return &sd->closure[sampled];
+}
+
+ccl_device_inline const ShaderClosure *shader_bssrdf_pick(ShaderData *sd,
+                                                          ccl_addr_space float3 *throughput,
+                                                          float *randu)
+{
+	int sampled = 0;
+
+	if(sd->num_closure > 1) {
+		/* Pick a BSDF or BSSRDF or based on sample weights. */
+		float sum_bsdf = 0.0f;
+		float sum_bssrdf = 0.0f;
+
+		for(int i = 0; i < sd->num_closure; i++) {
+			const ShaderClosure *sc = &sd->closure[i];
+
+			if(CLOSURE_IS_BSDF(sc->type)) {
+				sum_bsdf += sc->sample_weight;
+			}
+			else if(CLOSURE_IS_BSSRDF(sc->type)) {
+				sum_bssrdf += sc->sample_weight;
+			}
+		}
+
+		float r = (*randu)*(sum_bsdf + sum_bssrdf);
+		float partial_sum = 0.0f;
+
+		for(int i = 0; i < sd->num_closure; i++) {
+			const ShaderClosure *sc = &sd->closure[i];
+
+			if(CLOSURE_IS_BSDF_OR_BSSRDF(sc->type)) {
+				float next_sum = partial_sum + sc->sample_weight;
+
+				if(r < next_sum) {
+					if(CLOSURE_IS_BSDF(sc->type)) {
+						*throughput *= (sum_bsdf + sum_bssrdf) / sum_bsdf;
+						return NULL;
+					}
+					else {
+						*throughput *= (sum_bsdf + sum_bssrdf) / sum_bssrdf;
+						sampled = i;
+
+						/* Rescale to reuse for direction sample, to better
+						 * preserve stratifaction. */
+						*randu = (r - partial_sum) / sc->sample_weight;
+						break;
+					}
+				}
+
+				partial_sum = next_sum;
+			}
 		}
 	}
 
-	const ShaderClosure *sc = &sd->closure[sampled];
+	return &sd->closure[sampled];
+}
+
+ccl_device_inline int shader_bsdf_sample(KernelGlobals *kg,
+                                         ShaderData *sd,
+                                         float randu, float randv,
+                                         BsdfEval *bsdf_eval,
+                                         float3 *omega_in,
+                                         differential3 *domega_in,
+                                         float *pdf)
+{
+	const ShaderClosure *sc = shader_bsdf_pick(sd, &randu);
+	if(!sc) {
+		*pdf = 0.0f;
+		return LABEL_NONE;
+	}
+
+	/* BSSRDF should already have been handled elsewhere. */
+	kernel_assert(CLOSURE_IS_BSDF(sc->type));
 
 	int label;
 	float3 eval;
@@ -632,7 +729,7 @@ ccl_device_inline int shader_bsdf_sample(KernelGlobals *kg,
 
 		if(sd->num_closure > 1) {
 			float sweight = sc->sample_weight;
-			_shader_bsdf_multi_eval(kg, sd, *omega_in, pdf, sampled, bsdf_eval, *pdf*sweight, sweight);
+			_shader_bsdf_multi_eval(kg, sd, *omega_in, pdf, sc, bsdf_eval, *pdf*sweight, sweight);
 		}
 	}
 
@@ -868,11 +965,10 @@ ccl_device float3 shader_holdout_eval(KernelGlobals *kg, ShaderData *sd)
 /* Surface Evaluation */
 
 ccl_device void shader_eval_surface(KernelGlobals *kg, ShaderData *sd,
-	ccl_addr_space PathState *state, float randb, int path_flag)
+	ccl_addr_space PathState *state, int path_flag)
 {
 	sd->num_closure = 0;
 	sd->num_closure_extra = 0;
-	sd->randb_closure = randb;
 
 #ifdef __OSL__
 	if(kg->osl)
@@ -903,7 +999,6 @@ ccl_device float3 shader_eval_background(KernelGlobals *kg, ShaderData *sd,
 {
 	sd->num_closure = 0;
 	sd->num_closure_extra = 0;
-	sd->randb_closure = 0.0f;
 
 #ifdef __SVM__
 #ifdef __OSL__
@@ -985,17 +1080,22 @@ ccl_device int shader_volume_phase_sample(KernelGlobals *kg, const ShaderData *s
 				sum += sc->sample_weight;
 		}
 
-		float r = sd->randb_closure*sum;
-		sum = 0.0f;
+		float r = randu*sum;
+		float partial_sum = 0.0f;
 
 		for(sampled = 0; sampled < sd->num_closure; sampled++) {
 			const ShaderClosure *sc = &sd->closure[sampled];
 			
 			if(CLOSURE_IS_PHASE(sc->type)) {
-				sum += sc->sample_weight;
+				float next_sum = partial_sum + sc->sample_weight;
 
-				if(r <= sum)
+				if(r <= next_sum) {
+					/* Rescale to reuse for BSDF direction sample. */
+					randu = (r - partial_sum) / sc->sample_weight;
 					break;
+				}
+
+				partial_sum = next_sum;
 			}
 		}
 
@@ -1099,7 +1199,6 @@ ccl_device void shader_eval_displacement(KernelGlobals *kg, ShaderData *sd, ccl_
 {
 	sd->num_closure = 0;
 	sd->num_closure_extra = 0;
-	sd->randb_closure = 0.0f;
 
 	/* this will modify sd->P */
 #ifdef __SVM__
diff --git a/intern/cycles/kernel/kernel_shadow.h b/intern/cycles/kernel/kernel_shadow.h
index e02494ec1b0..065f9b184e2 100644
--- a/intern/cycles/kernel/kernel_shadow.h
+++ b/intern/cycles/kernel/kernel_shadow.h
@@ -86,7 +86,6 @@ ccl_device_forceinline bool shadow_handle_transparent_isect(
 		shader_eval_surface(kg,
 		                    shadow_sd,
 		                    state,
-		                    0.0f,
 		                    PATH_RAY_SHADOW);
 		path_state_modify_bounce(state, false);
 		*throughput *= shader_bsdf_transparency(kg, shadow_sd);
diff --git a/intern/cycles/kernel/kernel_subsurface.h b/intern/cycles/kernel/kernel_subsurface.h
index 26ec6383b73..23a09e5e2ca 100644
--- a/intern/cycles/kernel/kernel_subsurface.h
+++ b/intern/cycles/kernel/kernel_subsurface.h
@@ -28,87 +28,31 @@ CCL_NAMESPACE_BEGIN
  * - try to reduce one sample model variance
  */
 
-#define BSSRDF_MULTI_EVAL
-
-ccl_device ShaderClosure *subsurface_scatter_pick_closure(KernelGlobals *kg, ShaderData *sd, float *probability)
-{
-	/* sum sample weights of bssrdf and bsdf */
-	float bsdf_sum = 0.0f;
-	float bssrdf_sum = 0.0f;
-
-	for(int i = 0; i < sd->num_closure; i++) {
-		ShaderClosure *sc = &sd->closure[i];
-		
-		if(CLOSURE_IS_BSDF(sc->type))
-			bsdf_sum += sc->sample_weight;
-		else if(CLOSURE_IS_BSSRDF(sc->type))
-			bssrdf_sum += sc->sample_weight;
-	}
-
-	/* use bsdf or bssrdf? */
-	float r = sd->randb_closure*(bsdf_sum + bssrdf_sum);
-
-	if(r < bsdf_sum) {
-		/* use bsdf, and adjust randb so we can reuse it for picking a bsdf */
-		sd->randb_closure = r/bsdf_sum;
-		*probability = (bsdf_sum > 0.0f)? (bsdf_sum + bssrdf_sum)/bsdf_sum: 1.0f;
-		return NULL;
-	}
-
-	/* use bssrdf */
-	r -= bsdf_sum;
-
-	float sum = 0.0f;
-
-	for(int i = 0; i < sd->num_closure; i++) {
-		ShaderClosure *sc = &sd->closure[i];
-		
-		if(CLOSURE_IS_BSSRDF(sc->type)) {
-			sum += sc->sample_weight;
-
-			if(r <= sum) {
-				sd->randb_closure = (r - (sum - sc->sample_weight))/sc->sample_weight;
-
-#ifdef BSSRDF_MULTI_EVAL
-				*probability = (bssrdf_sum > 0.0f)? (bsdf_sum + bssrdf_sum)/bssrdf_sum: 1.0f;
-#else
-				*probability = (bssrdf_sum > 0.0f)? (bsdf_sum + bssrdf_sum)/sc->sample_weight: 1.0f;
-#endif
-				return sc;
-			}
-		}
-	}
-
-	/* should never happen */
-	sd->randb_closure = 0.0f;
-	*probability = 1.0f;
-	return NULL;
-}
-
 ccl_device_inline float3 subsurface_scatter_eval(ShaderData *sd,
-                                                 ShaderClosure *sc,
+                                                 const ShaderClosure *sc,
                                                  float disk_r,
                                                  float r,
                                                  bool all)
 {
-#ifdef BSSRDF_MULTI_EVAL
 	/* this is the veach one-sample model with balance heuristic, some pdf
 	 * factors drop out when using balance heuristic weighting */
 	float3 eval_sum = make_float3(0.0f, 0.0f, 0.0f);
 	float pdf_sum = 0.0f;
-	float sample_weight_sum = 0.0f;
-	int num_bssrdf = 0;
+	float sample_weight_inv = 0.0f;
 
-	for(int i = 0; i < sd->num_closure; i++) {
-		sc = &sd->closure[i];
-		
-		if(CLOSURE_IS_BSSRDF(sc->type)) {
-			float sample_weight = (all)? 1.0f: sc->sample_weight;
-			sample_weight_sum += sample_weight;
+	if(!all) {
+		float sample_weight_sum = 0.0f;
+
+		for(int i = 0; i < sd->num_closure; i++) {
+			sc = &sd->closure[i];
+
+			if(CLOSURE_IS_BSSRDF(sc->type)) {
+				sample_weight_sum += sc->sample_weight;
+			}
 		}
-	}
 
-	float sample_weight_inv = 1.0f/sample_weight_sum;
+		sample_weight_inv = 1.0f/sample_weight_sum;
+	}
 
 	for(int i = 0; i < sd->num_closure; i++) {
 		sc = &sd->closure[i];
@@ -125,25 +69,16 @@ ccl_device_inline float3 subsurface_scatter_eval(ShaderData *sd,
 			/* TODO power heuristic is not working correct here */
 			eval_sum += sc->weight*pdf; //*sample_weight*disk_pdf;
 			pdf_sum += sample_weight*disk_pdf; //*sample_weight*disk_pdf;
-
-			num_bssrdf++;
 		}
 	}
 
 	return (pdf_sum > 0.0f)? eval_sum / pdf_sum : make_float3(0.0f, 0.0f, 0.0f);
-#else
-	float pdf = bssrdf_pdf(pick_sc, r);
-	float disk_pdf = bssrdf_pdf(pick_sc, disk_r);
-
-	return pick_sc->weight * pdf / disk_pdf;
-#endif
 }
 
 /* replace closures with a single diffuse bsdf closure after scatter step */
-ccl_device void subsurface_scatter_setup_diffuse_bsdf(ShaderData *sd, ShaderClosure *sc, float3 weight, bool hit, float3 N)
+ccl_device void subsurface_scatter_setup_diffuse_bsdf(ShaderData *sd, const ShaderClosure *sc, float3 weight, bool hit, float3 N)
 {
 	sd->flag &= ~SD_CLOSURE_FLAGS;
-	sd->randb_closure = 0.0f;
 	sd->num_closure = 0;
 	sd->num_closure_extra = 0;
 
@@ -219,7 +154,7 @@ ccl_device void subsurface_color_bump_blur(KernelGlobals *kg,
 
 	if(bump || texture_blur > 0.0f) {
 		/* average color and normal at incoming point */
-		shader_eval_surface(kg, sd, state, 0.0f, state_flag);
+		shader_eval_surface(kg, sd, state, state_flag);
 		float3 in_color = shader_bssrdf_sum(sd, (bump)? N: NULL, NULL);
 
 		/* we simply divide out the average color and multiply with the average
@@ -242,7 +177,7 @@ ccl_device_inline int subsurface_scatter_multi_intersect(
         KernelGlobals *kg,
         SubsurfaceIntersection *ss_isect,
         ShaderData *sd,
-        ShaderClosure *sc,
+        const ShaderClosure *sc,
         uint *lcg_state,
         float disk_u,
         float disk_v,
@@ -255,26 +190,20 @@ ccl_device_inline int subsurface_scatter_multi_intersect(
 	disk_N = sd->Ng;
 	make_orthonormals(disk_N, &disk_T, &disk_B);
 
-	/* reusing variable for picking the closure gives a bit nicer stratification
-	 * for path tracer, for branched we do all closures so it doesn't help */
-	float axisu = (all)? disk_u: sd->randb_closure;
-
-	if(axisu < 0.5f) {
+	if(disk_u < 0.5f) {
 		pick_pdf_N = 0.5f;
 		pick_pdf_T = 0.25f;
 		pick_pdf_B = 0.25f;
-		if(all)
-			disk_u *= 2.0f;
+		disk_u *= 2.0f;
 	}
-	else if(axisu < 0.75f) {
+	else if(disk_u < 0.75f) {
 		float3 tmp = disk_N;
 		disk_N = disk_T;
 		disk_T = tmp;
 		pick_pdf_N = 0.25f;
 		pick_pdf_T = 0.5f;
 		pick_pdf_B = 0.25f;
-		if(all)
-			disk_u = (disk_u - 0.5f)*4.0f;
+		disk_u = (disk_u - 0.5f)*4.0f;
 	}
 	else {
 		float3 tmp = disk_N;
@@ -283,8 +212,7 @@ ccl_device_inline int subsurface_scatter_multi_intersect(
 		pick_pdf_N = 0.25f;
 		pick_pdf_T = 0.25f;
 		pick_pdf_B = 0.5f;
-		if(all)
-			disk_u = (disk_u - 0.75f)*4.0f;
+		disk_u = (disk_u - 0.75f)*4.0f;
 	}
 
 	/* sample point on disk */
@@ -390,7 +318,7 @@ ccl_device_noinline void subsurface_scatter_multi_setup(
         ShaderData *sd,
         ccl_addr_space PathState *state,
         int state_flag,
-        ShaderClosure *sc,
+        const ShaderClosure *sc,
         bool all)
 {
 #ifdef __SPLIT_KERNEL__
@@ -419,7 +347,7 @@ ccl_device_noinline void subsurface_scatter_multi_setup(
 
 /* subsurface scattering step, from a point on the surface to another nearby point on the same object */
 ccl_device void subsurface_scatter_step(KernelGlobals *kg, ShaderData *sd, ccl_addr_space PathState *state,
-	int state_flag, ShaderClosure *sc, uint *lcg_state, float disk_u, float disk_v, bool all)
+	int state_flag, const ShaderClosure *sc, uint *lcg_state, float disk_u, float disk_v, bool all)
 {
 	float3 eval = make_float3(0.0f, 0.0f, 0.0f);
 
@@ -430,18 +358,20 @@ ccl_device void subsurface_scatter_step(KernelGlobals *kg, ShaderData *sd, ccl_a
 	disk_N = sd->Ng;
 	make_orthonormals(disk_N, &disk_T, &disk_B);
 
-	if(sd->randb_closure < 0.5f) {
+	if(disk_u < 0.5f) {
 		pick_pdf_N = 0.5f;
 		pick_pdf_T = 0.25f;
 		pick_pdf_B = 0.25f;
+		disk_u *= 2.0f;
 	}
-	else if(sd->randb_closure < 0.75f) {
+	else if(disk_u < 0.75f) {
 		float3 tmp = disk_N;
 		disk_N = disk_T;
 		disk_T = tmp;
 		pick_pdf_N = 0.25f;
 		pick_pdf_T = 0.5f;
 		pick_pdf_B = 0.25f;
+		disk_u = (disk_u - 0.5f)*4.0f;
 	}
 	else {
 		float3 tmp = disk_N;
@@ -450,6 +380,7 @@ ccl_device void subsurface_scatter_step(KernelGlobals *kg, ShaderData *sd, ccl_a
 		pick_pdf_N = 0.25f;
 		pick_pdf_T = 0.25f;
 		pick_pdf_B = 0.5f;
+		disk_u = (disk_u - 0.75f)*4.0f;
 	}
 
 	/* sample point on disk */
diff --git a/intern/cycles/kernel/kernel_types.h b/intern/cycles/kernel/kernel_types.h
index 1b4e926ca28..1853fab1967 100644
--- a/intern/cycles/kernel/kernel_types.h
+++ b/intern/cycles/kernel/kernel_types.h
@@ -281,31 +281,21 @@ enum PathTraceDimension {
 	PRNG_FILTER_V = 1,
 	PRNG_LENS_U = 2,
 	PRNG_LENS_V = 3,
-#ifdef __CAMERA_MOTION__
 	PRNG_TIME = 4,
 	PRNG_UNUSED_0 = 5,
 	PRNG_UNUSED_1 = 6,	/* for some reason (6, 7) is a bad sobol pattern */
 	PRNG_UNUSED_2 = 7,  /* with a low number of samples (< 64) */
-#endif
-	PRNG_BASE_NUM = 8,
+	PRNG_BASE_NUM = 10,
 
 	PRNG_BSDF_U = 0,
 	PRNG_BSDF_V = 1,
-	PRNG_BSDF = 2,
-	PRNG_UNUSED3 = 3,
-	PRNG_LIGHT_U = 4,
-	PRNG_LIGHT_V = 5,
-	PRNG_LIGHT_TERMINATE = 6,
-	PRNG_TERMINATE = 7,
-
-#ifdef __VOLUME__
-	PRNG_PHASE_U = 8,
-	PRNG_PHASE_V = 9,
-	PRNG_PHASE = 10,
-	PRNG_SCATTER_DISTANCE = 11,
-#endif
-
-	PRNG_BOUNCE_NUM = 12,
+	PRNG_LIGHT_U = 2,
+	PRNG_LIGHT_V = 3,
+	PRNG_LIGHT_TERMINATE = 4,
+	PRNG_TERMINATE = 5,
+	PRNG_PHASE_CHANNEL = 6,
+	PRNG_SCATTER_DISTANCE = 7,
+	PRNG_BOUNCE_NUM = 8,
 };
 
 enum SamplingPattern {
diff --git a/intern/cycles/kernel/kernel_volume.h b/intern/cycles/kernel/kernel_volume.h
index d8e8e192ab2..d9c310a893e 100644
--- a/intern/cycles/kernel/kernel_volume.h
+++ b/intern/cycles/kernel/kernel_volume.h
@@ -379,13 +379,12 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_homogeneous(
 
 		/* pick random color channel, we use the Veach one-sample
 		 * model with balance heuristic for the channels */
-		float rphase = path_state_rng_1D_for_decision(kg, state, PRNG_PHASE);
+		float rphase = path_state_rng_1D(kg, state, PRNG_PHASE_CHANNEL);
 		int channel = (int)(rphase*3.0f);
-		sd->randb_closure = rphase*3.0f - channel;
 
 		/* decide if we will hit or miss */
 		bool scatter = true;
-		float xi = path_state_rng_1D_for_decision(kg, state, PRNG_SCATTER_DISTANCE);
+		float xi = path_state_rng_1D(kg, state, PRNG_SCATTER_DISTANCE);
 
 		if(probalistic_scatter) {
 			float sample_sigma_t = kernel_volume_channel_get(sigma_t, channel);
@@ -483,10 +482,9 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_heterogeneous_distance(
 
 	/* pick random color channel, we use the Veach one-sample
 	 * model with balance heuristic for the channels */
-	float xi = path_state_rng_1D_for_decision(kg, state, PRNG_SCATTER_DISTANCE);
-	float rphase = path_state_rng_1D_for_decision(kg, state, PRNG_PHASE);
+	float xi = path_state_rng_1D(kg, state, PRNG_SCATTER_DISTANCE);
+	float rphase = path_state_rng_1D(kg, state, PRNG_PHASE_CHANNEL);
 	int channel = (int)(rphase*3.0f);
-	sd->randb_closure = rphase*3.0f - channel;
 	bool has_scatter = false;
 
 	for(int i = 0; i < max_steps; i++) {
@@ -843,7 +841,6 @@ ccl_device VolumeIntegrateResult kernel_volume_decoupled_scatter(
 	/* pick random color channel, we use the Veach one-sample
 	 * model with balance heuristic for the channels */
 	int channel = (int)(rphase*3.0f);
-	sd->randb_closure = rphase*3.0f - channel;
 	float xi = rscatter;
 
 	/* probabilistic scattering decision based on transmittance */
diff --git a/intern/cycles/kernel/kernel_work_stealing.h b/intern/cycles/kernel/kernel_work_stealing.h
index 28fc5ce1c30..0c11158e8da 100644
--- a/intern/cycles/kernel/kernel_work_stealing.h
+++ b/intern/cycles/kernel/kernel_work_stealing.h
@@ -27,90 +27,54 @@ CCL_NAMESPACE_BEGIN
 #  pragma OPENCL EXTENSION cl_khr_global_int32_base_atomics : enable
 #endif
 
-ccl_device_inline uint kernel_total_work_size(KernelGlobals *kg)
-{
-	return kernel_split_params.w * kernel_split_params.h * kernel_split_params.num_samples;
-}
-
-ccl_device_inline uint kernel_num_work_pools(KernelGlobals *kg)
-{
-	return ccl_global_size(0) * ccl_global_size(1) / WORK_POOL_SIZE;
-}
-
-ccl_device_inline uint work_pool_from_ray_index(KernelGlobals *kg, uint ray_index)
-{
-	return ray_index / WORK_POOL_SIZE;
-}
-
-ccl_device_inline uint work_pool_work_size(KernelGlobals *kg, uint work_pool)
-{
-	uint total_work_size = kernel_total_work_size(kg);
-	uint num_pools = kernel_num_work_pools(kg);
-
-	if(work_pool >= num_pools || work_pool * WORK_POOL_SIZE >= total_work_size) {
-		return 0;
-	}
-
-	uint work_size = (total_work_size / (num_pools * WORK_POOL_SIZE)) * WORK_POOL_SIZE;
-
-	uint remainder = (total_work_size % (num_pools * WORK_POOL_SIZE));
-	if(work_pool < remainder / WORK_POOL_SIZE) {
-		work_size += WORK_POOL_SIZE;
-	}
-	else if(work_pool == remainder / WORK_POOL_SIZE) {
-		work_size += remainder % WORK_POOL_SIZE;
-	}
-
-	return work_size;
-}
-
-ccl_device_inline uint get_global_work_index(KernelGlobals *kg, uint work_index, uint ray_index)
-{
-	uint num_pools = kernel_num_work_pools(kg);
-	uint pool = work_pool_from_ray_index(kg, ray_index);
-
-	return (work_index / WORK_POOL_SIZE) * (num_pools * WORK_POOL_SIZE)
-	       + (pool * WORK_POOL_SIZE)
-	       + (work_index % WORK_POOL_SIZE);
-}
-
 /* Returns true if there is work */
-ccl_device bool get_next_work(KernelGlobals *kg, ccl_private uint *work_index, uint ray_index)
+ccl_device bool get_next_work(KernelGlobals *kg,
+                              uint thread_index,
+                              ccl_private uint *global_work_index)
 {
-	uint work_pool = work_pool_from_ray_index(kg, ray_index);
-	uint pool_size = work_pool_work_size(kg, work_pool);
+	uint total_work_size = kernel_split_params.w
+	                     * kernel_split_params.h
+	                     * kernel_split_params.num_samples;
 
-	if(pool_size == 0) {
+	/* With a small amount of work there may be more threads than work due to
+	 * rounding up of global size, stop such threads immediately. */
+	if(thread_index >= total_work_size) {
 		return false;
 	}
 
-	*work_index = atomic_fetch_and_inc_uint32(&kernel_split_params.work_pools[work_pool]);
-	return (*work_index < pool_size);
-}
+	/* Increase atomic work index counter in pool. */
+	uint pool = thread_index / WORK_POOL_SIZE;
+	uint work_index = atomic_fetch_and_inc_uint32(&kernel_split_params.work_pools[pool]);
 
-/* This function assumes that the passed `work` is valid. */
-/* Decode sample number w.r.t. assigned `work`. */
-ccl_device uint get_work_sample(KernelGlobals *kg, uint work_index, uint ray_index)
-{
-	return get_global_work_index(kg, work_index, ray_index) / (kernel_split_params.w * kernel_split_params.h);
-}
+	/* Map per-pool work index to a global work index. */
+	uint global_size = ccl_global_size(0) * ccl_global_size(1);
+	kernel_assert(global_size % WORK_POOL_SIZE == 0);
+	kernel_assert(thread_index < global_size);
 
-/* Decode pixel and tile position w.r.t. assigned `work`. */
-ccl_device void get_work_pixel_tile_position(KernelGlobals *kg,
-                             ccl_private uint *pixel_x,
-                             ccl_private uint *pixel_y,
-                             ccl_private uint *tile_x,
-                             ccl_private uint *tile_y,
-                             uint work_index,
-                             uint ray_index)
-{
-	uint pixel_index = get_global_work_index(kg, work_index, ray_index) % (kernel_split_params.w*kernel_split_params.h);
+	*global_work_index = (work_index / WORK_POOL_SIZE) * global_size
+	                   + (pool * WORK_POOL_SIZE)
+	                   + (work_index % WORK_POOL_SIZE);
 
-	*tile_x = pixel_index % kernel_split_params.w;
-	*tile_y = pixel_index / kernel_split_params.w;
+	/* Test if all work for this pool is done. */
+	return (*global_work_index < total_work_size);
+}
 
-	*pixel_x = *tile_x + kernel_split_params.x;
-	*pixel_y = *tile_y + kernel_split_params.y;
+/* Map global work index to pixel X/Y and sample. */
+ccl_device_inline void get_work_pixel(KernelGlobals *kg,
+                                      uint global_work_index,
+                                      ccl_private uint *x,
+                                      ccl_private uint *y,
+                                      ccl_private uint *sample)
+{
+	uint tile_pixels = kernel_split_params.w * kernel_split_params.h;
+	uint sample_offset = global_work_index / tile_pixels;
+	uint pixel_offset = global_work_index - sample_offset * tile_pixels;
+	uint y_offset = pixel_offset / kernel_split_params.w;
+	uint x_offset = pixel_offset - y_offset * kernel_split_params.w;
+
+	*x = kernel_split_params.x + x_offset;
+	*y = kernel_split_params.y + y_offset;
+	*sample = kernel_split_params.start_sample + sample_offset;
 }
 
 CCL_NAMESPACE_END
diff --git a/intern/cycles/kernel/split/kernel_buffer_update.h b/intern/cycles/kernel/split/kernel_buffer_update.h
index 7b4d1299c12..c9e7deddafa 100644
--- a/intern/cycles/kernel/split/kernel_buffer_update.h
+++ b/intern/cycles/kernel/split/kernel_buffer_update.h
@@ -84,14 +84,9 @@ ccl_device void kernel_buffer_update(KernelGlobals *kg,
 	ccl_global float3 *throughput = &kernel_split_state.throughput[ray_index];
 
 	if(IS_STATE(ray_state, ray_index, RAY_UPDATE_BUFFER)) {
-		uint work_index = kernel_split_state.work_array[ray_index];
-		uint sample = get_work_sample(kg, work_index, ray_index) + kernel_split_params.start_sample;
-
-		uint tile_x, tile_y, pixel_x, pixel_y;
-		get_work_pixel_tile_position(kg, &pixel_x, &pixel_y, &tile_x, &tile_y, work_index, ray_index);
-
-		ccl_global float *buffer = kernel_split_params.buffer;
-		buffer += (kernel_split_params.offset + pixel_x + pixel_y*stride) * kernel_data.film.pass_stride;
+		uint sample = state->sample;
+		uint buffer_offset = kernel_split_state.buffer_offset[ray_index];
+		ccl_global float *buffer = kernel_split_params.buffer + buffer_offset;
 
 		/* accumulate result in output buffer */
 		kernel_write_result(kg, buffer, sample, L);
@@ -102,31 +97,26 @@ ccl_device void kernel_buffer_update(KernelGlobals *kg,
 	if(IS_STATE(ray_state, ray_index, RAY_TO_REGENERATE)) {
 		/* We have completed current work; So get next work */
 		uint work_index;
-		int valid_work = get_next_work(kg, &work_index, ray_index);
-		if(!valid_work) {
+		if(!get_next_work(kg, ray_index, &work_index)) {
 			/* If work is invalid, this means no more work is available and the thread may exit */
 			ASSIGN_RAY_STATE(ray_state, ray_index, RAY_INACTIVE);
 		}
 
 		if(IS_STATE(ray_state, ray_index, RAY_TO_REGENERATE)) {
-			kernel_split_state.work_array[ray_index] = work_index;
-			/* Get the sample associated with the current work */
-			uint sample = get_work_sample(kg, work_index, ray_index) + kernel_split_params.start_sample;
-			/* Get pixel and tile position associated with current work */
-			uint tile_x, tile_y, pixel_x, pixel_y;
-			get_work_pixel_tile_position(kg, &pixel_x, &pixel_y, &tile_x, &tile_y, work_index, ray_index);
-
-			/* Remap rng_state according to the current work */
+			uint x, y, sample;
+			get_work_pixel(kg, work_index, &x, &y, &sample);
+
+			/* Remap rng_state to current pixel. */
 			ccl_global uint *rng_state = kernel_split_params.rng_state;
-			rng_state += kernel_split_params.offset + pixel_x + pixel_y*stride;
+			rng_state += kernel_split_params.offset + x + y*stride;
 
-			/* Remap buffer according to the current work */
-			ccl_global float *buffer = kernel_split_params.buffer;
-			buffer += (kernel_split_params.offset + pixel_x + pixel_y*stride) * kernel_data.film.pass_stride;
+			/* Store buffer offset for writing to passes. */
+			uint buffer_offset = (kernel_split_params.offset + x + y*stride) * kernel_data.film.pass_stride;
+			kernel_split_state.buffer_offset[ray_index] = buffer_offset;
 
 			/* Initialize random numbers and ray. */
 			uint rng_hash;
-			kernel_path_trace_setup(kg, rng_state, sample, pixel_x, pixel_y, &rng_hash, ray);
+			kernel_path_trace_setup(kg, rng_state, sample, x, y, &rng_hash, ray);
 
 			if(ray->t != 0.0f) {
 				/* Initialize throughput, path radiance, Ray, PathState;
@@ -145,6 +135,7 @@ ccl_device void kernel_buffer_update(KernelGlobals *kg,
 				/* These rays do not participate in path-iteration. */
 				float4 L_rad = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
 				/* Accumulate result in output buffer. */
+				ccl_global float *buffer = kernel_split_params.buffer + buffer_offset;
 				kernel_write_pass_float4(buffer, sample, L_rad);
 
 				ASSIGN_RAY_STATE(ray_state, ray_index, RAY_TO_REGENERATE);
diff --git a/intern/cycles/kernel/split/kernel_holdout_emission_blurring_pathtermination_ao.h b/intern/cycles/kernel/split/kernel_holdout_emission_blurring_pathtermination_ao.h
index 9036b1e473d..dffd291012d 100644
--- a/intern/cycles/kernel/split/kernel_holdout_emission_blurring_pathtermination_ao.h
+++ b/intern/cycles/kernel/split/kernel_holdout_emission_blurring_pathtermination_ao.h
@@ -90,8 +90,6 @@ ccl_device void kernel_holdout_emission_blurring_pathtermination_ao(
 	if(ray_index != QUEUE_EMPTY_SLOT) {
 #endif
 
-	int stride = kernel_split_params.stride;
-
 	ccl_global PathState *state = 0x0;
 	float3 throughput;
 
@@ -99,15 +97,8 @@ ccl_device void kernel_holdout_emission_blurring_pathtermination_ao(
 	ShaderData *sd = &kernel_split_state.sd[ray_index];
 
 	if(IS_STATE(ray_state, ray_index, RAY_ACTIVE)) {
-		uint work_index = kernel_split_state.work_array[ray_index];
-		uint pixel_x, pixel_y, tile_x, tile_y;
-		get_work_pixel_tile_position(kg, &pixel_x, &pixel_y,
-		                        &tile_x, &tile_y,
-		                        work_index,
-		                        ray_index);
-
-		ccl_global float *buffer = kernel_split_params.buffer;
-		buffer += (kernel_split_params.offset + pixel_x + pixel_y * stride) * kernel_data.film.pass_stride;
+		uint buffer_offset = kernel_split_state.buffer_offset[ray_index];
+		ccl_global float *buffer = kernel_split_params.buffer + buffer_offset;
 
 		ccl_global Ray *ray = &kernel_split_state.ray[ray_index];
 		ShaderData *emission_sd = &kernel_split_state.sd_DL_shadow[ray_index];
@@ -140,7 +131,7 @@ ccl_device void kernel_holdout_emission_blurring_pathtermination_ao(
 			kernel_split_path_end(kg, ray_index);
 		}
 		else if(probability < 1.0f) {
-			float terminate = path_state_rng_1D_for_decision(kg, state, PRNG_TERMINATE);
+			float terminate = path_state_rng_1D(kg, state, PRNG_TERMINATE);
 			if(terminate >= probability) {
 				kernel_split_path_end(kg, ray_index);
 			}
diff --git a/intern/cycles/kernel/split/kernel_path_init.h b/intern/cycles/kernel/split/kernel_path_init.h
index c75931855b2..0ab2289348b 100644
--- a/intern/cycles/kernel/split/kernel_path_init.h
+++ b/intern/cycles/kernel/split/kernel_path_init.h
@@ -29,38 +29,32 @@ ccl_device void kernel_path_init(KernelGlobals *kg) {
 	 */
 	kernel_split_state.ray_state[ray_index] = RAY_ACTIVE;
 
-	uint work_index = 0;
 	/* Get work. */
-	if(!get_next_work(kg, &work_index, ray_index)) {
+	uint work_index;
+	if(!get_next_work(kg, ray_index, &work_index)) {
 		/* No more work, mark ray as inactive */
 		kernel_split_state.ray_state[ray_index] = RAY_INACTIVE;
 
 		return;
 	}
 
-	/* Get the sample associated with the work. */
-	uint sample = get_work_sample(kg, work_index, ray_index) + kernel_split_params.start_sample;
-
-	/* Get pixel and tile position associated with the work. */
-	uint pixel_x, pixel_y, tile_x, tile_y;
-	get_work_pixel_tile_position(kg, &pixel_x, &pixel_y,
-	                             &tile_x, &tile_y,
-	                             work_index,
-	                             ray_index);
-	kernel_split_state.work_array[ray_index] = work_index;
+	uint x, y, sample;
+	get_work_pixel(kg, work_index, &x, &y, &sample);
 
+	/* Remap rng_state and buffer to current pixel. */
 	ccl_global uint *rng_state = kernel_split_params.rng_state;
-	rng_state += kernel_split_params.offset + pixel_x + pixel_y*kernel_split_params.stride;
+	rng_state += kernel_split_params.offset + x + y*kernel_split_params.stride;
 
-	ccl_global float *buffer = kernel_split_params.buffer;
-	buffer += (kernel_split_params.offset + pixel_x + pixel_y * kernel_split_params.stride) * kernel_data.film.pass_stride;
+	/* Store buffer offset for writing to passes. */
+	uint buffer_offset = (kernel_split_params.offset + x + y*kernel_split_params.stride) * kernel_data.film.pass_stride;
+	kernel_split_state.buffer_offset[ray_index] = buffer_offset;
 
 	/* Initialize random numbers and ray. */
 	uint rng_hash;
 	kernel_path_trace_setup(kg,
 	                        rng_state,
 	                        sample,
-	                        pixel_x, pixel_y,
+	                        x, y,
 	                        &rng_hash,
 	                        &kernel_split_state.ray[ray_index]);
 
@@ -84,6 +78,7 @@ ccl_device void kernel_path_init(KernelGlobals *kg) {
 		/* These rays do not participate in path-iteration. */
 		float4 L_rad = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
 		/* Accumulate result in output buffer. */
+		ccl_global float *buffer = kernel_split_params.buffer + buffer_offset;
 		kernel_write_pass_float4(buffer, sample, L_rad);
 		ASSIGN_RAY_STATE(kernel_split_state.ray_state, ray_index, RAY_TO_REGENERATE);
 	}
diff --git a/intern/cycles/kernel/split/kernel_shader_eval.h b/intern/cycles/kernel/split/kernel_shader_eval.h
index eac29dcd0d1..7032461b04a 100644
--- a/intern/cycles/kernel/split/kernel_shader_eval.h
+++ b/intern/cycles/kernel/split/kernel_shader_eval.h
@@ -50,20 +50,16 @@ ccl_device void kernel_shader_eval(KernelGlobals *kg)
 	if(IS_STATE(ray_state, ray_index, RAY_ACTIVE)) {
 		ccl_global PathState *state = &kernel_split_state.path_state[ray_index];
 
-#ifndef __BRANCHED_PATH__
-		float rbsdf = path_state_rng_1D_for_decision(kg, state, PRNG_BSDF);
-		shader_eval_surface(kg, &kernel_split_state.sd[ray_index], state, rbsdf, state->flag);
-#else
-		float rbsdf = 0.0f;
-
-		if(!kernel_data.integrator.branched || IS_FLAG(ray_state, ray_index, RAY_BRANCHED_INDIRECT)) {
-			rbsdf = path_state_rng_1D_for_decision(kg, state, PRNG_BSDF);
-
+		shader_eval_surface(kg, &kernel_split_state.sd[ray_index], state, state->flag);
+#ifdef __BRANCHED_PATH__
+		if(kernel_data.integrator.branched) {
+			shader_merge_closures(&kernel_split_state.sd[ray_index]);
+		}
+		else
+#endif
+		{
+			shader_prepare_closures(&kernel_split_state.sd[ray_index], state);
 		}
-
-		shader_eval_surface(kg, &kernel_split_state.sd[ray_index], state, rbsdf, state->flag);
-		shader_merge_closures(&kernel_split_state.sd[ray_index]);
-#endif  /* __BRANCHED_PATH__ */
 	}
 }
 
diff --git a/intern/cycles/kernel/split/kernel_split_data_types.h b/intern/cycles/kernel/split/kernel_split_data_types.h
index e08afc22b20..c58c8463f5c 100644
--- a/intern/cycles/kernel/split/kernel_split_data_types.h
+++ b/intern/cycles/kernel/split/kernel_split_data_types.h
@@ -122,7 +122,7 @@ typedef ccl_global struct SplitBranchedState {
 	SPLIT_DATA_ENTRY(ccl_global int, is_lamp, 1) \
 	SPLIT_DATA_ENTRY(ccl_global Ray, light_ray, 1) \
 	SPLIT_DATA_ENTRY(ccl_global int, queue_data, (NUM_QUEUES*2)) /* TODO(mai): this is too large? */ \
-	SPLIT_DATA_ENTRY(ccl_global uint, work_array, 1) \
+	SPLIT_DATA_ENTRY(ccl_global uint, buffer_offset, 1) \
 	SPLIT_DATA_ENTRY(ShaderData, sd, 1) \
 	SPLIT_DATA_ENTRY(ShaderData, sd_DL_shadow, 1) \
 	SPLIT_DATA_SUBSURFACE_ENTRIES \
diff --git a/intern/cycles/kernel/split/kernel_subsurface_scatter.h b/intern/cycles/kernel/split/kernel_subsurface_scatter.h
index a487e53df5c..3b957856aea 100644
--- a/intern/cycles/kernel/split/kernel_subsurface_scatter.h
+++ b/intern/cycles/kernel/split/kernel_subsurface_scatter.h
@@ -250,20 +250,17 @@ ccl_device void kernel_subsurface_scatter(KernelGlobals *kg)
 #ifdef __BRANCHED_PATH__
 			}
 			else if(IS_FLAG(ray_state, ray_index, RAY_BRANCHED_INDIRECT)) {
-				float bssrdf_probability;
-				ShaderClosure *sc = subsurface_scatter_pick_closure(kg, sd, &bssrdf_probability);
+				float bssrdf_u, bssrdf_v;
+				path_state_rng_2D(kg,
+				                  state,
+				                  PRNG_BSDF_U,
+				                  &bssrdf_u, &bssrdf_v);
 
-				/* modify throughput for picking bssrdf or bsdf */
-				*throughput *= bssrdf_probability;
+				const ShaderClosure *sc = shader_bssrdf_pick(sd, throughput, &bssrdf_u);
 
 				/* do bssrdf scatter step if we picked a bssrdf closure */
 				if(sc) {
 					uint lcg_state = lcg_state_init_addrspace(state, 0x68bc21eb);
-					float bssrdf_u, bssrdf_v;
-					path_state_rng_2D(kg,
-					                  state,
-					                  PRNG_BSDF_U,
-					                  &bssrdf_u, &bssrdf_v);
 					subsurface_scatter_step(kg,
 					                        sd,
 					                        state,
diff --git a/intern/cycles/util/util_optimization.h b/intern/cycles/util/util_optimization.h
index 0382c0811dd..3c5785c4807 100644
--- a/intern/cycles/util/util_optimization.h
+++ b/intern/cycles/util/util_optimization.h
@@ -25,6 +25,9 @@
 
 #if defined(i386) || defined(_M_IX86)
 
+/* We require minimum SSE2 support on x86, so auto enable. */
+#  define __KERNEL_SSE2__
+
 #  ifdef WITH_KERNEL_SSE2
 #    define WITH_CYCLES_OPTIMIZED_KERNEL_SSE2
 #  endif