Sample as Lamp option for world shaders, to enable multiple importance sampling.

By default lighting from the world is computed solely with indirect light
sampling. However for more complex environment maps this can be too noisy, as
sampling the BSDF may not easily find the highlights in the environment map
image. By enabling this option, the world background will be sampled as a lamp,
with lighter parts automatically given more samples.

Map Resolution specifies the size of the importance map (res x res). Before
rendering starts, an importance map is generated by "baking" a grayscale image
from the world shader. This will then be used to determine which parts of the
background are light and so should receive more samples than darker parts.
Higher resolutions will result in more accurate sampling but take more setup
time and memory.

Patch by Mike Farnsworth, thanks!

1 files changed, 65 insertions, 19 deletions

diff --git a/intern/cycles/kernel/kernel_emission.h b/intern/cycles/kernel/kernel_emission.h
index b81db721eb3..51698f3a9bd 100644
--- a/intern/cycles/kernel/kernel_emission.h
+++ b/intern/cycles/kernel/kernel_emission.h
@@ -25,21 +25,31 @@ __device float3 direct_emissive_eval(KernelGlobals *kg, float rando,
 {
 	/* setup shading at emitter */
 	ShaderData sd;
-
-	shader_setup_from_sample(kg, &sd, ls->P, ls->Ng, I, ls->shader, ls->object, ls->prim, u, v);
-	ls->Ng = sd.Ng;
-
-	/* no path flag, we're evaluating this for all closures. that's weak but
-	   we'd have to do multiple evaluations otherwise */
-	shader_eval_surface(kg, &sd, rando, 0);
-	
 	float3 eval;
 
-	/* evaluate emissive closure */
-	if(sd.flag & SD_EMISSION)
-		eval = shader_emissive_eval(kg, &sd);
-	else
-		eval = make_float3(0.0f, 0.0f, 0.0f);
+	if(ls->type == LIGHT_BACKGROUND) {
+		Ray ray;
+		ray.D = ls->D;
+		ray.P = ls->P;
+		ray.dP.dx = make_float3(0.0f, 0.0f, 0.0f);
+		ray.dP.dy = make_float3(0.0f, 0.0f, 0.0f);
+		shader_setup_from_background(kg, &sd, &ray);
+		eval = shader_eval_background(kg, &sd, 0);
+	}
+	else {
+		shader_setup_from_sample(kg, &sd, ls->P, ls->Ng, I, ls->shader, ls->object, ls->prim, u, v);
+		ls->Ng = sd.Ng;
+
+		/* no path flag, we're evaluating this for all closures. that's weak but
+		   we'd have to do multiple evaluations otherwise */
+		shader_eval_surface(kg, &sd, rando, 0);
+
+		/* evaluate emissive closure */
+		if(sd.flag & SD_EMISSION)
+			eval = shader_emissive_eval(kg, &sd);
+		else
+			eval = make_float3(0.0f, 0.0f, 0.0f);
+	}
 
 	shader_release(kg, &sd);
 
@@ -51,25 +61,31 @@ __device bool direct_emission(KernelGlobals *kg, ShaderData *sd, int lindex,
 {
 	LightSample ls;
 
+	float pdf = -1.0f;
+
 #ifdef __MULTI_LIGHT__
 	if(lindex != -1) {
 		/* sample position on a specified light */
-		light_select(kg, lindex, randu, randv, sd->P, &ls);
+		light_select(kg, lindex, randu, randv, sd->P, &ls, &pdf);
 	}
 	else
 #endif
 	{
 		/* sample a light and position on int */
-		light_sample(kg, randt, randu, randv, sd->P, &ls);
+		light_sample(kg, randt, randu, randv, sd->P, &ls, &pdf);
 	}
 
 	/* compute pdf */
-	float pdf = light_sample_pdf(kg, &ls, -ls.D, ls.t);
+	if(pdf < 0.0f)
+		pdf = light_sample_pdf(kg, &ls, -ls.D, ls.t);
+
+	if(pdf == 0.0f)
+		return false;
 
 	/* evaluate closure */
 	*eval = direct_emissive_eval(kg, rando, &ls, randu, randv, -ls.D);
 
-	if(is_zero(*eval) || pdf == 0.0f)
+	if(is_zero(*eval))
 		return false;
 
 	/* todo: use visbility flag to skip lights */
@@ -83,7 +99,7 @@ __device bool direct_emission(KernelGlobals *kg, ShaderData *sd, int lindex,
 	if(is_zero(*eval))
 		return false;
 
-	if(ls.prim != ~0) {
+	if(ls.prim != ~0 || ls.type == LIGHT_BACKGROUND) {
 		/* multiple importance sampling */
 		float mis_weight = power_heuristic(pdf, bsdf_pdf);
 		*eval *= mis_weight;
@@ -125,7 +141,8 @@ __device float3 indirect_emission(KernelGlobals *kg, ShaderData *sd, float t, in
 	float3 L = shader_emissive_eval(kg, sd);
 
 	if(!(path_flag & PATH_RAY_MIS_SKIP) && (sd->flag & SD_SAMPLE_AS_LIGHT)) {
-		/* multiple importance sampling */
+		/* multiple importance sampling, get triangle light pdf,
+		   and compute weight with respect to BSDF pdf */
 		float pdf = triangle_light_pdf(kg, sd->Ng, sd->I, t);
 		float mis_weight = power_heuristic(bsdf_pdf, pdf);
 
@@ -135,5 +152,34 @@ __device float3 indirect_emission(KernelGlobals *kg, ShaderData *sd, float t, in
 	return L;
 }
 
+/* Indirect Background */
+
+__device float3 indirect_background(KernelGlobals *kg, Ray *ray, int path_flag, float bsdf_pdf)
+{
+#ifdef __BACKGROUND__
+	/* evaluate background closure */
+	ShaderData sd;
+	shader_setup_from_background(kg, &sd, ray);
+	float3 L = shader_eval_background(kg, &sd, path_flag);
+	shader_release(kg, &sd);
+
+	/* check if background light exists or if we should skip pdf */
+	int res = kernel_data.integrator.pdf_background_res;
+
+	if(!(path_flag & PATH_RAY_MIS_SKIP) && res) {
+		/* multiple importance sampling, get background light pdf for ray
+		   direction, and compute weight with respect to BSDF pdf */
+		float pdf = background_light_pdf(kg, ray->D);
+		float mis_weight = power_heuristic(bsdf_pdf, pdf);
+
+		return L*mis_weight;
+	}
+
+	return L;
+#else
+	return make_float3(0.8f, 0.8f, 0.8f);
+#endif
+}
+
 CCL_NAMESPACE_END