Cycles: Implement approximate reflectance profiles

Using this paper:

  http://graphics.pixar.com/library/ApproxBSSRDF/paper.pdf

This model gives less blurry results than the Cubic and Gaussian
we had implemented:

- Cubic: https://developer.blender.org/F279670
- Burley: https://developer.blender.org/F279671

The model is called "Christensen-Burley" in the interface, which
actually should be read as "Physically based" or "Realistic".

Reviewers: juicyfruit, dingto, lukasstockner97, brecht

Reviewed By: brecht, dingto

Subscribers: robocyte

Differential Revision: https://developer.blender.org/D1759

5 files changed, 42 insertions, 0 deletions

diff --git a/intern/cycles/kernel/osl/osl_bssrdf.cpp b/intern/cycles/kernel/osl/osl_bssrdf.cpp
index 7f286c76c46..da4afb138f6 100644
--- a/intern/cycles/kernel/osl/osl_bssrdf.cpp
+++ b/intern/cycles/kernel/osl/osl_bssrdf.cpp
@@ -105,5 +105,34 @@ ClosureParam *closure_bssrdf_gaussian_params()
 
 CCLOSURE_PREPARE(closure_bssrdf_gaussian_prepare, GaussianBSSRDFClosure)
 
+/* Burley */
+
+class BurleyBSSRDFClosure : public CBSSRDFClosure {
+public:
+	BurleyBSSRDFClosure()
+	{}
+
+	void setup()
+	{
+		sc.type = CLOSURE_BSSRDF_BURLEY_ID;
+		sc.data0 = fabsf(average(radius));
+	}
+};
+
+ClosureParam *closure_bssrdf_burley_params()
+{
+	static ClosureParam params[] = {
+		CLOSURE_FLOAT3_PARAM(BurleyBSSRDFClosure, sc.N),
+		CLOSURE_FLOAT3_PARAM(BurleyBSSRDFClosure, radius),
+		CLOSURE_FLOAT_PARAM(BurleyBSSRDFClosure, sc.data1),
+		CLOSURE_FLOAT3_PARAM(BurleyBSSRDFClosure, albedo),
+		CLOSURE_STRING_KEYPARAM(BurleyBSSRDFClosure, label, "label"),
+		CLOSURE_FINISH_PARAM(BurleyBSSRDFClosure)
+	};
+	return params;
+}
+
+CCLOSURE_PREPARE(closure_bssrdf_burley_prepare, BurleyBSSRDFClosure)
+
 CCL_NAMESPACE_END
 
diff --git a/intern/cycles/kernel/osl/osl_bssrdf.h b/intern/cycles/kernel/osl/osl_bssrdf.h
index 6aee2c28ea8..d81ecade543 100644
--- a/intern/cycles/kernel/osl/osl_bssrdf.h
+++ b/intern/cycles/kernel/osl/osl_bssrdf.h
@@ -49,6 +49,7 @@ class CBSSRDFClosure : public CClosurePrimitive {
 public:
 	ShaderClosure sc;
 	float3 radius;
+	float3 albedo;
 
 	CBSSRDFClosure() : CClosurePrimitive(BSSRDF) { }
 	int scattering() const { return LABEL_DIFFUSE; }
diff --git a/intern/cycles/kernel/osl/osl_closures.cpp b/intern/cycles/kernel/osl/osl_closures.cpp
index 461ce8f7598..95b8cea0922 100644
--- a/intern/cycles/kernel/osl/osl_closures.cpp
+++ b/intern/cycles/kernel/osl/osl_closures.cpp
@@ -236,6 +236,8 @@ void OSLShader::register_closures(OSLShadingSystem *ss_)
 		closure_bssrdf_cubic_params(), closure_bssrdf_cubic_prepare);
 	register_closure(ss, "bssrdf_gaussian", id++,
 		closure_bssrdf_gaussian_params(), closure_bssrdf_gaussian_prepare);
+	register_closure(ss, "bssrdf_burley", id++,
+		closure_bssrdf_burley_params(), closure_bssrdf_burley_prepare);
 
 	register_closure(ss, "hair_reflection", id++,
 		bsdf_hair_reflection_params(), bsdf_hair_reflection_prepare);
diff --git a/intern/cycles/kernel/osl/osl_closures.h b/intern/cycles/kernel/osl/osl_closures.h
index d8a3f77d0dd..526c03557f7 100644
--- a/intern/cycles/kernel/osl/osl_closures.h
+++ b/intern/cycles/kernel/osl/osl_closures.h
@@ -50,6 +50,7 @@ OSL::ClosureParam *closure_bsdf_diffuse_ramp_params();
 OSL::ClosureParam *closure_bsdf_phong_ramp_params();
 OSL::ClosureParam *closure_bssrdf_cubic_params();
 OSL::ClosureParam *closure_bssrdf_gaussian_params();
+OSL::ClosureParam *closure_bssrdf_burley_params();
 OSL::ClosureParam *closure_henyey_greenstein_volume_params();
 
 void closure_emission_prepare(OSL::RendererServices *, int id, void *data);
@@ -60,6 +61,7 @@ void closure_bsdf_diffuse_ramp_prepare(OSL::RendererServices *, int id, void *da
 void closure_bsdf_phong_ramp_prepare(OSL::RendererServices *, int id, void *data);
 void closure_bssrdf_cubic_prepare(OSL::RendererServices *, int id, void *data);
 void closure_bssrdf_gaussian_prepare(OSL::RendererServices *, int id, void *data);
+void closure_bssrdf_burley_prepare(OSL::RendererServices *, int id, void *data);
 void closure_henyey_greenstein_volume_prepare(OSL::RendererServices *, int id, void *data);
 
 #define CCLOSURE_PREPARE(name, classname)          \
diff --git a/intern/cycles/kernel/osl/osl_shader.cpp b/intern/cycles/kernel/osl/osl_shader.cpp
index 8f459c8b267..8acc042cd2c 100644
--- a/intern/cycles/kernel/osl/osl_shader.cpp
+++ b/intern/cycles/kernel/osl/osl_shader.cpp
@@ -281,11 +281,17 @@ static void flatten_surface_closure_tree(ShaderData *sd, int path_flag,
 							if(path_flag & PATH_RAY_DIFFUSE_ANCESTOR)
 								bssrdf->radius = make_float3(0.0f, 0.0f, 0.0f);
 
+							float3 albedo =
+							        (bssrdf->sc.type == CLOSURE_BSSRDF_BURLEY_ID)
+							                ? bssrdf->albedo
+							                : make_float3(0.0f, 0.0f, 0.0f);
+
 							/* create one closure for each color channel */
 							if(fabsf(weight.x) > 0.0f) {
 								sc.weight = make_float3(weight.x, 0.0f, 0.0f);
 								sc.data0 = bssrdf->radius.x;
 								sc.data1 = 0.0f;
+								sc.data2 = albedo.x;
 								sd->flag |= bssrdf_setup(&sc, sc.type);
 								sd->closure[sd->num_closure++] = sc;
 							}
@@ -294,6 +300,7 @@ static void flatten_surface_closure_tree(ShaderData *sd, int path_flag,
 								sc.weight = make_float3(0.0f, weight.y, 0.0f);
 								sc.data0 = bssrdf->radius.y;
 								sc.data1 = 0.0f;
+								sc.data2 = albedo.y;
 								sd->flag |= bssrdf_setup(&sc, sc.type);
 								sd->closure[sd->num_closure++] = sc;
 							}
@@ -302,6 +309,7 @@ static void flatten_surface_closure_tree(ShaderData *sd, int path_flag,
 								sc.weight = make_float3(0.0f, 0.0f, weight.z);
 								sc.data0 = bssrdf->radius.z;
 								sc.data1 = 0.0f;
+								sc.data2 = albedo.z;
 								sd->flag |= bssrdf_setup(&sc, sc.type);
 								sd->closure[sd->num_closure++] = sc;
 							}