Cycles: MIS for lamps now loops over all lamps instead of picking one.

Probably will not be noticed in most scenes. This helps reduce noise when you
have multiple lamps with MIS enabled, at the cost of some performance, but from
testing some scenes this seems better.

3 files changed, 28 insertions, 27 deletions

diff --git a/intern/cycles/kernel/kernel_emission.h b/intern/cycles/kernel/kernel_emission.h
index 8812bbb36ce..44899e0bf97 100644
--- a/intern/cycles/kernel/kernel_emission.h
+++ b/intern/cycles/kernel/kernel_emission.h
@@ -183,38 +183,42 @@ ccl_device_noinline float3 indirect_primitive_emission(KernelGlobals *kg, Shader
 
 /* Indirect Lamp Emission */
 
-ccl_device_noinline bool indirect_lamp_emission(KernelGlobals *kg, PathState *state, Ray *ray, float randt, float3 *emission)
+ccl_device_noinline bool indirect_lamp_emission(KernelGlobals *kg, PathState *state, Ray *ray, float3 *emission)
 {
-	LightSample ls;
-	int lamp = lamp_light_eval_sample(kg, randt);
+	bool hit_lamp = false;
 
-	if(lamp == LAMP_NONE)
-		return false;
+	*emission = make_float3(0.0f, 0.0f, 0.0f);
 
-	if(!lamp_light_eval(kg, lamp, ray->P, ray->D, ray->t, &ls))
-		return false;
+	for(int lamp = 0; lamp < kernel_data.integrator.num_all_lights; lamp++) {
+		LightSample ls;
+
+		if(!lamp_light_eval(kg, lamp, ray->P, ray->D, ray->t, &ls))
+			continue;
 
 #ifdef __PASSES__
-	/* use visibility flag to skip lights */
-	if(ls.shader & SHADER_EXCLUDE_ANY) {
-		if(((ls.shader & SHADER_EXCLUDE_DIFFUSE) && (state->flag & PATH_RAY_DIFFUSE)) ||
-		   ((ls.shader & SHADER_EXCLUDE_GLOSSY) && (state->flag & PATH_RAY_GLOSSY)) ||
-		   ((ls.shader & SHADER_EXCLUDE_TRANSMIT) && (state->flag & PATH_RAY_TRANSMIT)))
-			return false;
-	}
+		/* use visibility flag to skip lights */
+		if(ls.shader & SHADER_EXCLUDE_ANY) {
+			if(((ls.shader & SHADER_EXCLUDE_DIFFUSE) && (state->flag & PATH_RAY_DIFFUSE)) ||
+			   ((ls.shader & SHADER_EXCLUDE_GLOSSY) && (state->flag & PATH_RAY_GLOSSY)) ||
+			   ((ls.shader & SHADER_EXCLUDE_TRANSMIT) && (state->flag & PATH_RAY_TRANSMIT)))
+				continue;
+		}
 #endif
 
-	float3 L = direct_emissive_eval(kg, &ls, -ray->D, ray->dD, ls.t, ray->time, state->bounce, state->transparent_bounce);
+		float3 L = direct_emissive_eval(kg, &ls, -ray->D, ray->dD, ls.t, ray->time, state->bounce, state->transparent_bounce);
 
-	if(!(state->flag & PATH_RAY_MIS_SKIP)) {
-		/* multiple importance sampling, get regular light pdf,
-		 * and compute weight with respect to BSDF pdf */
-		float mis_weight = power_heuristic(state->ray_pdf, ls.pdf);
-		L *= mis_weight;
+		if(!(state->flag & PATH_RAY_MIS_SKIP)) {
+			/* multiple importance sampling, get regular light pdf,
+			 * and compute weight with respect to BSDF pdf */
+			float mis_weight = power_heuristic(state->ray_pdf, ls.pdf);
+			L *= mis_weight;
+		}
+
+		*emission += L;
+		hit_lamp = true;
 	}
 
-	*emission = L;
-	return true;
+	return hit_lamp;
 }
 
 /* Indirect Background */
diff --git a/intern/cycles/kernel/kernel_light.h b/intern/cycles/kernel/kernel_light.h
index ffda44fee57..ac432d3fe04 100644
--- a/intern/cycles/kernel/kernel_light.h
+++ b/intern/cycles/kernel/kernel_light.h
@@ -421,7 +421,6 @@ ccl_device bool lamp_light_eval(KernelGlobals *kg, int lamp, float3 P, float3 D,
 	/* compute pdf */
 	if(ls->t != FLT_MAX)
 		ls->pdf *= lamp_light_pdf(kg, ls->Ng, -ls->D, ls->t);
-	ls->eval_fac *= kernel_data.integrator.inv_pdf_lights;
 
 	return true;
 }
diff --git a/intern/cycles/kernel/kernel_path.h b/intern/cycles/kernel/kernel_path.h
index f9dc9f3c50f..1ca6bd38ba9 100644
--- a/intern/cycles/kernel/kernel_path.h
+++ b/intern/cycles/kernel/kernel_path.h
@@ -240,10 +240,9 @@ ccl_device void kernel_path_indirect(KernelGlobals *kg, RNG *rng, Ray ray, ccl_g
 			light_ray.dP = ray.dP;
 
 			/* intersect with lamp */
-			float light_t = path_state_rng_1D(kg, rng, &state, PRNG_LIGHT);
 			float3 emission;
 
-			if(indirect_lamp_emission(kg, &state, &light_ray, light_t, &emission))
+			if(indirect_lamp_emission(kg, &state, &light_ray, &emission))
 				path_radiance_accum_emission(L, throughput, emission, state.bounce);
 		}
 #endif
@@ -624,10 +623,9 @@ ccl_device float4 kernel_path_integrate(KernelGlobals *kg, RNG *rng, int sample,
 			light_ray.dP = ray.dP;
 
 			/* intersect with lamp */
-			float light_t = path_state_rng_1D(kg, rng, &state, PRNG_LIGHT);
 			float3 emission;
 
-			if(indirect_lamp_emission(kg, &state, &light_ray, light_t, &emission))
+			if(indirect_lamp_emission(kg, &state, &light_ray, &emission))
 				path_radiance_accum_emission(&L, throughput, emission, state.bounce);
 		}
 #endif