Cycles: Subsurface Scattering

New features:

* Bump mapping now works with SSS
* Texture Blur factor for SSS, see the documentation for details:
http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Nodes/Shaders#Subsurface_Scattering

Work in progress for feedback:

Initial implementation of the "BSSRDF Importance Sampling" paper, which uses
a different importance sampling method. It gives better quality results in
many ways, with the availability of both Cubic and Gaussian falloff functions,
but also tends to be more noisy when using the progressive integrator and does
not give great results with some geometry. It works quite well for the
non-progressive integrator and is often less noisy there.

This code may still change a lot, so unless you're testing it may be best to
stick to the Compatible falloff function.

Skin test render and file that takes advantage of the gaussian falloff:
http://www.pasteall.org/pic/show.php?id=57661
http://www.pasteall.org/pic/show.php?id=57662
http://www.pasteall.org/blend/23501

1 files changed, 71 insertions, 46 deletions

diff --git a/intern/cycles/kernel/kernel_shader.h b/intern/cycles/kernel/kernel_shader.h
index 5dd12f98b9c..2c86cc5e227 100644
--- a/intern/cycles/kernel/kernel_shader.h
+++ b/intern/cycles/kernel/kernel_shader.h
@@ -184,52 +184,32 @@ __device_inline void shader_setup_from_subsurface(KernelGlobals *kg, ShaderData
 	sd->flag = kernel_tex_fetch(__object_flag, sd->object);
 	sd->prim = kernel_tex_fetch(__prim_index, isect->prim);
 
-#ifdef __HAIR__
-	if(kernel_tex_fetch(__prim_segment, isect->prim) != ~0) {
-		/* Strand Shader setting*/
-		float4 curvedata = kernel_tex_fetch(__curves, sd->prim);
-
-		sd->shader = __float_as_int(curvedata.z);
-		sd->segment = isect->segment;
-
-		float tcorr = isect->t;
-		if(kernel_data.curve.curveflags & CURVE_KN_POSTINTERSECTCORRECTION)
-			tcorr = (isect->u < 0)? tcorr + sqrtf(isect->v) : tcorr - sqrtf(isect->v);
-
-		sd->P = bvh_curve_refine(kg, sd, isect, ray, tcorr);
-	}
-	else {
-#endif
-		/* fetch triangle data */
-		float4 Ns = kernel_tex_fetch(__tri_normal, sd->prim);
-		float3 Ng = make_float3(Ns.x, Ns.y, Ns.z);
-		sd->shader = __float_as_int(Ns.w);
+	/* fetch triangle data */
+	float4 Ns = kernel_tex_fetch(__tri_normal, sd->prim);
+	float3 Ng = make_float3(Ns.x, Ns.y, Ns.z);
+	sd->shader = __float_as_int(Ns.w);
 
 #ifdef __HAIR__
-		sd->segment = ~0;
+	sd->segment = ~0;
 #endif
 
 #ifdef __UV__
-		sd->u = isect->u;
-		sd->v = isect->v;
+	sd->u = isect->u;
+	sd->v = isect->v;
 #endif
 
-		/* vectors */
-		sd->P = bvh_triangle_refine(kg, sd, isect, ray);
-		sd->Ng = Ng;
-		sd->N = Ng;
-		
-		/* smooth normal */
-		if(sd->shader & SHADER_SMOOTH_NORMAL)
-			sd->N = triangle_smooth_normal(kg, sd->prim, sd->u, sd->v);
+	/* vectors */
+	sd->P = bvh_triangle_refine_subsurface(kg, sd, isect, ray);
+	sd->Ng = Ng;
+	sd->N = Ng;
+	
+	/* smooth normal */
+	if(sd->shader & SHADER_SMOOTH_NORMAL)
+		sd->N = triangle_smooth_normal(kg, sd->prim, sd->u, sd->v);
 
 #ifdef __DPDU__
-		/* dPdu/dPdv */
-		triangle_dPdudv(kg, &sd->dPdu, &sd->dPdv, sd->prim);
-#endif
-
-#ifdef __HAIR__
-	}
+	/* dPdu/dPdv */
+	triangle_dPdudv(kg, &sd->dPdu, &sd->dPdv, sd->prim);
 #endif
 
 	sd->flag |= kernel_tex_fetch(__shader_flag, (sd->shader & SHADER_MASK)*2);
@@ -468,6 +448,8 @@ __device_inline void shader_setup_from_background(KernelGlobals *kg, ShaderData
 __device_inline void _shader_bsdf_multi_eval(KernelGlobals *kg, const ShaderData *sd, const float3 omega_in, float *pdf,
 	int skip_bsdf, 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;
@@ -706,34 +688,34 @@ __device float3 shader_bsdf_subsurface(KernelGlobals *kg, ShaderData *sd)
 #endif
 }
 
-__device float3 shader_bsdf_ao(KernelGlobals *kg, ShaderData *sd, float ao_factor, float3 *N)
+__device float3 shader_bsdf_ao(KernelGlobals *kg, ShaderData *sd, float ao_factor, float3 *N_)
 {
 #ifdef __MULTI_CLOSURE__
 	float3 eval = make_float3(0.0f, 0.0f, 0.0f);
-
-	*N = make_float3(0.0f, 0.0f, 0.0f);
+	float3 N = make_float3(0.0f, 0.0f, 0.0f);
 
 	for(int i = 0; i< sd->num_closure; i++) {
 		ShaderClosure *sc = &sd->closure[i];
 
 		if(CLOSURE_IS_BSDF_DIFFUSE(sc->type)) {
 			eval += sc->weight*ao_factor;
-			*N += sc->N*average(sc->weight);
+			N += sc->N*average(sc->weight);
 		}
 		else if(CLOSURE_IS_AMBIENT_OCCLUSION(sc->type)) {
 			eval += sc->weight;
-			*N += sd->N*average(sc->weight);
+			N += sd->N*average(sc->weight);
 		}
 	}
 
-	if(is_zero(*N))
-		*N = sd->N;
+	if(is_zero(N))
+		N = sd->N;
 	else
-		*N = normalize(*N);
+		N = normalize(N);
 
+	*N_ = N;
 	return eval;
 #else
-	*N = sd->N;
+	*N_ = sd->N;
 
 	if(CLOSURE_IS_BSDF_DIFFUSE(sd->closure.type))
 		return sd->closure.weight*ao_factor;
@@ -744,6 +726,49 @@ __device float3 shader_bsdf_ao(KernelGlobals *kg, ShaderData *sd, float ao_facto
 #endif
 }
 
+__device float3 shader_bssrdf_sum(ShaderData *sd, float3 *N_, float *texture_blur_)
+{
+#ifdef __MULTI_CLOSURE__
+	float3 eval = make_float3(0.0f, 0.0f, 0.0f);
+	float3 N = make_float3(0.0f, 0.0f, 0.0f);
+	float texture_blur = 0.0f, weight_sum = 0.0f;
+
+	for(int i = 0; i< sd->num_closure; i++) {
+		ShaderClosure *sc = &sd->closure[i];
+
+		if(CLOSURE_IS_BSSRDF(sc->type)) {
+			float avg_weight = fabsf(average(sc->weight));
+
+			N += sc->N*avg_weight;
+			eval += sc->weight;
+			texture_blur += sc->data1*avg_weight;
+			weight_sum += avg_weight;
+		}
+	}
+
+	if(N_)
+		*N_ = (is_zero(N))? sd->N: normalize(N);
+
+	if(texture_blur_)
+		*texture_blur_ = texture_blur/weight_sum;
+	
+	return eval;
+#else
+	if(CLOSURE_IS_BSSRDF(sd->closure.type)) {
+		if(N_) *N_ = sd->closure.N;
+		if(texture_blur_) *texture_blur_ = sd->closure.data1;
+
+		return sd->closure.weight;
+	}
+	else {
+		if(N_) *N_ = sd->N;
+		if(texture_blur_) *texture_blur_ = 0.0f;
+
+		return make_float3(0.0f, 0.0f, 0.0f);
+	}
+#endif
+}
+
 /* Emission */
 
 __device float3 emissive_eval(KernelGlobals *kg, ShaderData *sd, ShaderClosure *sc)