Cycles: add Transparent Depth output to Light Path node.

This can for example be useful if you want to manually terminate the path at
some point and use a color other than black.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D454

14 files changed, 66 insertions, 37 deletions

diff --git a/intern/cycles/kernel/kernel_displace.h b/intern/cycles/kernel/kernel_displace.h
index c50e2166660..1935f72ce95 100644
--- a/intern/cycles/kernel/kernel_displace.h
+++ b/intern/cycles/kernel/kernel_displace.h
@@ -55,7 +55,7 @@ ccl_device void kernel_shader_evaluate(KernelGlobals *kg, ccl_global uint4 *inpu
 #endif
 
 		/* setup shader data */
-		shader_setup_from_background(kg, &sd, &ray, 0);
+		shader_setup_from_background(kg, &sd, &ray, 0, 0);
 
 		/* evaluate */
 		int flag = 0; /* we can't know which type of BSDF this is for */
diff --git a/intern/cycles/kernel/kernel_emission.h b/intern/cycles/kernel/kernel_emission.h
index bb61b2111fe..4c4f15c0e0a 100644
--- a/intern/cycles/kernel/kernel_emission.h
+++ b/intern/cycles/kernel/kernel_emission.h
@@ -19,7 +19,7 @@ CCL_NAMESPACE_BEGIN
 /* Direction Emission */
 
 ccl_device_noinline float3 direct_emissive_eval(KernelGlobals *kg, float rando,
-	LightSample *ls, float3 I, differential3 dI, float t, float time, int bounce)
+	LightSample *ls, float3 I, differential3 dI, float t, float time, int bounce, int transparent_bounce)
 {
 	/* setup shading at emitter */
 	ShaderData sd;
@@ -37,13 +37,13 @@ ccl_device_noinline float3 direct_emissive_eval(KernelGlobals *kg, float rando,
 		ray.dP = differential3_zero();
 		ray.dD = dI;
 
-		shader_setup_from_background(kg, &sd, &ray, bounce+1);
+		shader_setup_from_background(kg, &sd, &ray, bounce+1, transparent_bounce);
 		eval = shader_eval_background(kg, &sd, 0, SHADER_CONTEXT_EMISSION);
 	}
 	else
 #endif
 	{
-		shader_setup_from_sample(kg, &sd, ls->P, ls->Ng, I, ls->shader, ls->object, ls->prim, ls->u, ls->v, t, time, bounce+1);
+		shader_setup_from_sample(kg, &sd, ls->P, ls->Ng, I, ls->shader, ls->object, ls->prim, ls->u, ls->v, t, time, bounce+1, transparent_bounce);
 
 		ls->Ng = sd.Ng;
 
@@ -65,7 +65,7 @@ ccl_device_noinline float3 direct_emissive_eval(KernelGlobals *kg, float rando,
 
 ccl_device_noinline bool direct_emission(KernelGlobals *kg, ShaderData *sd, int lindex,
 	float randt, float rando, float randu, float randv, Ray *ray, BsdfEval *eval,
-	bool *is_lamp, int bounce)
+	bool *is_lamp, int bounce, int transparent_bounce)
 {
 	LightSample ls;
 
@@ -88,7 +88,7 @@ ccl_device_noinline bool direct_emission(KernelGlobals *kg, ShaderData *sd, int
 	differential3 dD = differential3_zero();
 
 	/* evaluate closure */
-	float3 light_eval = direct_emissive_eval(kg, rando, &ls, -ls.D, dD, ls.t, sd->time, bounce);
+	float3 light_eval = direct_emissive_eval(kg, rando, &ls, -ls.D, dD, ls.t, sd->time, bounce, transparent_bounce);
 
 	if(is_zero(light_eval))
 		return false;
@@ -183,7 +183,7 @@ ccl_device_noinline float3 indirect_primitive_emission(KernelGlobals *kg, Shader
 
 /* Indirect Lamp Emission */
 
-ccl_device_noinline bool indirect_lamp_emission(KernelGlobals *kg, Ray *ray, int path_flag, float bsdf_pdf, float randt, float3 *emission, int bounce)
+ccl_device_noinline bool indirect_lamp_emission(KernelGlobals *kg, Ray *ray, int path_flag, float bsdf_pdf, float randt, float3 *emission, int bounce, int transparent_bounce)
 {
 	LightSample ls;
 	int lamp = lamp_light_eval_sample(kg, randt);
@@ -204,7 +204,7 @@ ccl_device_noinline bool indirect_lamp_emission(KernelGlobals *kg, Ray *ray, int
 	}
 #endif
 
-	float3 L = direct_emissive_eval(kg, 0.0f, &ls, -ray->D, ray->dD, ls.t, ray->time, bounce);
+	float3 L = direct_emissive_eval(kg, 0.0f, &ls, -ray->D, ray->dD, ls.t, ray->time, bounce, transparent_bounce);
 
 	if(!(path_flag & PATH_RAY_MIS_SKIP)) {
 		/* multiple importance sampling, get regular light pdf,
@@ -219,7 +219,7 @@ ccl_device_noinline bool indirect_lamp_emission(KernelGlobals *kg, Ray *ray, int
 
 /* Indirect Background */
 
-ccl_device_noinline float3 indirect_background(KernelGlobals *kg, Ray *ray, int path_flag, float bsdf_pdf, int bounce)
+ccl_device_noinline float3 indirect_background(KernelGlobals *kg, Ray *ray, int path_flag, float bsdf_pdf, int bounce, int transparent_bounce)
 {
 #ifdef __BACKGROUND__
 	int shader = kernel_data.background.surface_shader;
@@ -235,7 +235,7 @@ ccl_device_noinline float3 indirect_background(KernelGlobals *kg, Ray *ray, int
 
 	/* evaluate background closure */
 	ShaderData sd;
-	shader_setup_from_background(kg, &sd, ray, bounce+1);
+	shader_setup_from_background(kg, &sd, ray, bounce+1, transparent_bounce);
 
 	float3 L = shader_eval_background(kg, &sd, path_flag, SHADER_CONTEXT_EMISSION);
 
diff --git a/intern/cycles/kernel/kernel_path.h b/intern/cycles/kernel/kernel_path.h
index 2764d0e0f19..14182dfb442 100644
--- a/intern/cycles/kernel/kernel_path.h
+++ b/intern/cycles/kernel/kernel_path.h
@@ -72,7 +72,7 @@ ccl_device_inline bool kernel_path_integrate_scatter_lighting(KernelGlobals *kg,
 			light_ray.time = sd->time;
 #endif
 
-			if(direct_emission(kg, sd, LAMP_NONE, light_t, light_o, light_u, light_v, &light_ray, &L_light, &is_lamp, state->bounce)) {
+			if(direct_emission(kg, sd, LAMP_NONE, light_t, light_o, light_u, light_v, &light_ray, &L_light, &is_lamp, state->bounce, state->transparent_bounce)) {
 				/* trace shadow ray */
 				float3 shadow;
 
@@ -157,7 +157,7 @@ ccl_device void kernel_branched_path_integrate_direct_lighting(KernelGlobals *kg
 					float light_u, light_v;
 					path_branched_rng_2D(kg, &lamp_rng, state, j, num_samples, PRNG_LIGHT_U, &light_u, &light_v);
 
-					if(direct_emission(kg, sd, i, 0.0f, 0.0f, light_u, light_v, &light_ray, &L_light, &is_lamp, state->bounce)) {
+					if(direct_emission(kg, sd, i, 0.0f, 0.0f, light_u, light_v, &light_ray, &L_light, &is_lamp, state->bounce, state->transparent_bounce)) {
 						/* trace shadow ray */
 						float3 shadow;
 
@@ -186,7 +186,7 @@ ccl_device void kernel_branched_path_integrate_direct_lighting(KernelGlobals *kg
 					if(kernel_data.integrator.num_all_lights)
 						light_t = 0.5f*light_t;
 
-					if(direct_emission(kg, sd, LAMP_NONE, light_t, 0.0f, light_u, light_v, &light_ray, &L_light, &is_lamp, state->bounce)) {
+					if(direct_emission(kg, sd, LAMP_NONE, light_t, 0.0f, light_u, light_v, &light_ray, &L_light, &is_lamp, state->bounce, state->transparent_bounce)) {
 						/* trace shadow ray */
 						float3 shadow;
 
@@ -204,7 +204,7 @@ ccl_device void kernel_branched_path_integrate_direct_lighting(KernelGlobals *kg
 			path_state_rng_2D(kg, rng, state, PRNG_LIGHT_U, &light_u, &light_v);
 
 			/* sample random light */
-			if(direct_emission(kg, sd, LAMP_NONE, light_t, 0.0f, light_u, light_v, &light_ray, &L_light, &is_lamp, state->bounce)) {
+			if(direct_emission(kg, sd, LAMP_NONE, light_t, 0.0f, light_u, light_v, &light_ray, &L_light, &is_lamp, state->bounce, state->transparent_bounce)) {
 				/* trace shadow ray */
 				float3 shadow;
 
@@ -248,7 +248,7 @@ ccl_device void kernel_path_indirect(KernelGlobals *kg, RNG *rng, Ray ray, ccl_g
 			float light_t = path_state_rng_1D(kg, rng, &state, PRNG_LIGHT);
 			float3 emission;
 
-			if(indirect_lamp_emission(kg, &light_ray, state.flag, state.ray_pdf, light_t, &emission, state.bounce))
+			if(indirect_lamp_emission(kg, &light_ray, state.flag, state.ray_pdf, light_t, &emission, state.bounce, state.transparent_bounce))
 				path_radiance_accum_emission(L, throughput, emission, state.bounce);
 		}
 #endif
@@ -275,7 +275,7 @@ ccl_device void kernel_path_indirect(KernelGlobals *kg, RNG *rng, Ray ray, ccl_g
 		if(!hit) {
 #ifdef __BACKGROUND__
 			/* sample background shader */
-			float3 L_background = indirect_background(kg, &ray, state.flag, state.ray_pdf, state.bounce);
+			float3 L_background = indirect_background(kg, &ray, state.flag, state.ray_pdf, state.bounce, state.transparent_bounce);
 			path_radiance_accum_background(L, throughput, L_background, state.bounce);
 #endif
 
@@ -284,7 +284,7 @@ ccl_device void kernel_path_indirect(KernelGlobals *kg, RNG *rng, Ray ray, ccl_g
 
 		/* setup shading */
 		ShaderData sd;
-		shader_setup_from_ray(kg, &sd, &isect, &ray, state.bounce);
+		shader_setup_from_ray(kg, &sd, &isect, &ray, state.bounce, state.transparent_bounce);
 		float rbsdf = path_state_rng_1D(kg, rng, &state, PRNG_BSDF);
 		shader_eval_surface(kg, &sd, rbsdf, state.flag, SHADER_CONTEXT_INDIRECT);
 #ifdef __BRANCHED_PATH__
@@ -490,7 +490,7 @@ ccl_device_inline bool kernel_path_integrate_lighting(KernelGlobals *kg, RNG *rn
 			light_ray.time = sd->time;
 #endif
 
-			if(direct_emission(kg, sd, LAMP_NONE, light_t, light_o, light_u, light_v, &light_ray, &L_light, &is_lamp, state->bounce)) {
+			if(direct_emission(kg, sd, LAMP_NONE, light_t, light_o, light_u, light_v, &light_ray, &L_light, &is_lamp, state->bounce, state->transparent_bounce)) {
 				/* trace shadow ray */
 				float3 shadow;
 
@@ -637,7 +637,7 @@ ccl_device float4 kernel_path_integrate(KernelGlobals *kg, RNG *rng, int sample,
 			float light_t = path_state_rng_1D(kg, rng, &state, PRNG_LIGHT);
 			float3 emission;
 
-			if(indirect_lamp_emission(kg, &light_ray, state.flag, state.ray_pdf, light_t, &emission, state.bounce))
+			if(indirect_lamp_emission(kg, &light_ray, state.flag, state.ray_pdf, light_t, &emission, state.bounce, state.transparent_bounce))
 				path_radiance_accum_emission(&L, throughput, emission, state.bounce);
 		}
 #endif
@@ -674,7 +674,7 @@ ccl_device float4 kernel_path_integrate(KernelGlobals *kg, RNG *rng, int sample,
 
 #ifdef __BACKGROUND__
 			/* sample background shader */
-			float3 L_background = indirect_background(kg, &ray, state.flag, state.ray_pdf, state.bounce);
+			float3 L_background = indirect_background(kg, &ray, state.flag, state.ray_pdf, state.bounce, state.transparent_bounce);
 			path_radiance_accum_background(&L, throughput, L_background, state.bounce);
 #endif
 
@@ -683,7 +683,7 @@ ccl_device float4 kernel_path_integrate(KernelGlobals *kg, RNG *rng, int sample,
 
 		/* setup shading */
 		ShaderData sd;
-		shader_setup_from_ray(kg, &sd, &isect, &ray, state.bounce);
+		shader_setup_from_ray(kg, &sd, &isect, &ray, state.bounce, state.transparent_bounce);
 		float rbsdf = path_state_rng_1D(kg, rng, &state, PRNG_BSDF);
 		shader_eval_surface(kg, &sd, rbsdf, state.flag, SHADER_CONTEXT_MAIN);
 
@@ -851,7 +851,7 @@ ccl_device float4 kernel_path_integrate(KernelGlobals *kg, RNG *rng, int sample,
 				light_ray.time = sd.time;
 #endif
 
-				if(direct_emission(kg, &sd, LAMP_NONE, light_t, light_o, light_u, light_v, &light_ray, &L_light, &is_lamp, state.bounce)) {
+				if(direct_emission(kg, &sd, LAMP_NONE, light_t, light_o, light_u, light_v, &light_ray, &L_light, &is_lamp, state.bounce, state.transparent_bounce)) {
 					/* trace shadow ray */
 					float3 shadow;
 
@@ -1100,7 +1100,7 @@ ccl_device float4 kernel_branched_path_integrate(KernelGlobals *kg, RNG *rng, in
 			VolumeSegment volume_segment;
 			ShaderData volume_sd;
 
-			shader_setup_from_volume(kg, &volume_sd, &volume_ray, state.bounce);
+			shader_setup_from_volume(kg, &volume_sd, &volume_ray, state.bounce, state.transparent_bounce);
 			kernel_volume_decoupled_record(kg, &state,
 				&volume_ray, &volume_sd, &volume_segment, heterogeneous);
 
@@ -1196,7 +1196,7 @@ ccl_device float4 kernel_branched_path_integrate(KernelGlobals *kg, RNG *rng, in
 
 #ifdef __BACKGROUND__
 			/* sample background shader */
-			float3 L_background = indirect_background(kg, &ray, state.flag, state.ray_pdf, state.bounce);
+			float3 L_background = indirect_background(kg, &ray, state.flag, state.ray_pdf, state.bounce, state.transparent_bounce);
 			path_radiance_accum_background(&L, throughput, L_background, state.bounce);
 #endif
 
@@ -1205,7 +1205,7 @@ ccl_device float4 kernel_branched_path_integrate(KernelGlobals *kg, RNG *rng, in
 
 		/* setup shading */
 		ShaderData sd;
-		shader_setup_from_ray(kg, &sd, &isect, &ray, state.bounce);
+		shader_setup_from_ray(kg, &sd, &isect, &ray, state.bounce, state.transparent_bounce);
 		shader_eval_surface(kg, &sd, 0.0f, state.flag, SHADER_CONTEXT_MAIN);
 		shader_merge_closures(&sd);
 
diff --git a/intern/cycles/kernel/kernel_shader.h b/intern/cycles/kernel/kernel_shader.h
index 7aa9cfbcccc..a731446954a 100644
--- a/intern/cycles/kernel/kernel_shader.h
+++ b/intern/cycles/kernel/kernel_shader.h
@@ -49,7 +49,7 @@ ccl_device void shader_setup_object_transforms(KernelGlobals *kg, ShaderData *sd
 #endif
 
 ccl_device void shader_setup_from_ray(KernelGlobals *kg, ShaderData *sd,
-	const Intersection *isect, const Ray *ray, int bounce)
+	const Intersection *isect, const Ray *ray, int bounce, int transparent_bounce)
 {
 #ifdef __INSTANCING__
 	sd->object = (isect->object == PRIM_NONE)? kernel_tex_fetch(__prim_object, isect->prim): isect->object;
@@ -67,6 +67,7 @@ ccl_device void shader_setup_from_ray(KernelGlobals *kg, ShaderData *sd,
 	sd->prim = kernel_tex_fetch(__prim_index, isect->prim);
 	sd->ray_length = isect->t;
 	sd->ray_depth = bounce;
+	sd->transparent_depth = transparent_bounce;
 
 #ifdef __UV__
 	sd->u = isect->u;
@@ -228,7 +229,7 @@ ccl_device_inline void shader_setup_from_subsurface(KernelGlobals *kg, ShaderDat
 
 ccl_device void shader_setup_from_sample(KernelGlobals *kg, ShaderData *sd,
 	const float3 P, const float3 Ng, const float3 I,
-	int shader, int object, int prim, float u, float v, float t, float time, int bounce)
+	int shader, int object, int prim, float u, float v, float t, float time, int bounce, int transparent_bounce)
 {
 	/* vectors */
 	sd->P = P;
@@ -250,6 +251,7 @@ ccl_device void shader_setup_from_sample(KernelGlobals *kg, ShaderData *sd,
 #endif
 	sd->ray_length = t;
 	sd->ray_depth = bounce;
+	sd->transparent_depth = transparent_bounce;
 
 	/* detect instancing, for non-instanced the object index is -object-1 */
 #ifdef __INSTANCING__
@@ -347,12 +349,12 @@ ccl_device void shader_setup_from_displace(KernelGlobals *kg, ShaderData *sd,
 
 	/* watch out: no instance transform currently */
 
-	shader_setup_from_sample(kg, sd, P, Ng, I, shader, object, prim, u, v, 0.0f, TIME_INVALID, 0);
+	shader_setup_from_sample(kg, sd, P, Ng, I, shader, object, prim, u, v, 0.0f, TIME_INVALID, 0, 0);
 }
 
 /* ShaderData setup from ray into background */
 
-ccl_device_inline void shader_setup_from_background(KernelGlobals *kg, ShaderData *sd, const Ray *ray, int bounce)
+ccl_device_inline void shader_setup_from_background(KernelGlobals *kg, ShaderData *sd, const Ray *ray, int bounce, int transparent_bounce)
 {
 	/* vectors */
 	sd->P = ray->D;
@@ -366,6 +368,7 @@ ccl_device_inline void shader_setup_from_background(KernelGlobals *kg, ShaderDat
 #endif
 	sd->ray_length = 0.0f;
 	sd->ray_depth = bounce;
+	sd->transparent_depth = transparent_bounce;
 
 #ifdef __INSTANCING__
 	sd->object = PRIM_NONE;
@@ -395,7 +398,7 @@ ccl_device_inline void shader_setup_from_background(KernelGlobals *kg, ShaderDat
 
 /* ShaderData setup from point inside volume */
 
-ccl_device_inline void shader_setup_from_volume(KernelGlobals *kg, ShaderData *sd, const Ray *ray, int bounce)
+ccl_device_inline void shader_setup_from_volume(KernelGlobals *kg, ShaderData *sd, const Ray *ray, int bounce, int transparent_bounce)
 {
 	/* vectors */
 	sd->P = ray->P;
@@ -409,6 +412,7 @@ ccl_device_inline void shader_setup_from_volume(KernelGlobals *kg, ShaderData *s
 #endif
 	sd->ray_length = 0.0f; /* todo: can we set this to some useful value? */
 	sd->ray_depth = bounce;
+	sd->transparent_depth = transparent_bounce;
 
 #ifdef __INSTANCING__
 	sd->object = PRIM_NONE; /* todo: fill this for texture coordinates */
diff --git a/intern/cycles/kernel/kernel_shadow.h b/intern/cycles/kernel/kernel_shadow.h
index 971dca38fc5..f53c032ca7b 100644
--- a/intern/cycles/kernel/kernel_shadow.h
+++ b/intern/cycles/kernel/kernel_shadow.h
@@ -95,7 +95,7 @@ ccl_device_inline bool shadow_blocked(KernelGlobals *kg, PathState *state, Ray *
 
 				/* setup shader data at surface */
 				ShaderData sd;
-				shader_setup_from_ray(kg, &sd, &isect, ray, state->bounce+1);
+				shader_setup_from_ray(kg, &sd, &isect, ray, ps.bounce+1, ps.transparent_bounce);
 
 				/* attenuation from transparent surface */
 				if(!(sd.flag & SD_HAS_ONLY_VOLUME)) {
diff --git a/intern/cycles/kernel/kernel_types.h b/intern/cycles/kernel/kernel_types.h
index 6b14b3935e0..5bc4ad5a13d 100644
--- a/intern/cycles/kernel/kernel_types.h
+++ b/intern/cycles/kernel/kernel_types.h
@@ -609,6 +609,9 @@ typedef struct ShaderData {
 	/* ray bounce depth */
 	int ray_depth;
 
+	/* ray transparent depth */
+	int transparent_depth;
+
 #ifdef __RAY_DIFFERENTIALS__
 	/* differential of P. these are orthogonal to Ng, not N */
 	differential3 dP;
diff --git a/intern/cycles/kernel/kernel_volume.h b/intern/cycles/kernel/kernel_volume.h
index 7928bdc4ff1..b3c97cfac7f 100644
--- a/intern/cycles/kernel/kernel_volume.h
+++ b/intern/cycles/kernel/kernel_volume.h
@@ -184,7 +184,7 @@ ccl_device void kernel_volume_shadow_heterogeneous(KernelGlobals *kg, PathState
 ccl_device_noinline void kernel_volume_shadow(KernelGlobals *kg, PathState *state, Ray *ray, float3 *throughput)
 {
 	ShaderData sd;
-	shader_setup_from_volume(kg, &sd, ray, state->bounce);
+	shader_setup_from_volume(kg, &sd, ray, state->bounce, state->transparent_bounce);
 
 	if(volume_stack_is_heterogeneous(kg, state->volume_stack))
 		kernel_volume_shadow_heterogeneous(kg, state, ray, &sd, throughput);
@@ -828,7 +828,7 @@ ccl_device_noinline VolumeIntegrateResult kernel_volume_integrate(KernelGlobals
 	/* debugging code to compare decoupled ray marching */
 	VolumeSegment segment;
 
-	shader_setup_from_volume(kg, sd, ray, state->bounce);
+	shader_setup_from_volume(kg, sd, ray, state->bounce, state->transparent_bounce);
 	kernel_volume_decoupled_record(kg, state, ray, sd, &segment, heterogeneous);
 
 	VolumeIntegrateResult result = kernel_volume_decoupled_scatter(kg, state, ray, sd, throughput, &tmp_rng, &segment);
@@ -837,7 +837,7 @@ ccl_device_noinline VolumeIntegrateResult kernel_volume_integrate(KernelGlobals
 
 	return result;
 #else
-	shader_setup_from_volume(kg, sd, ray, state->bounce);
+	shader_setup_from_volume(kg, sd, ray, state->bounce, state->transparent_bounce);
 
 	if(heterogeneous)
 		return kernel_volume_integrate_heterogeneous(kg, state, ray, sd, L, throughput, &tmp_rng);
diff --git a/intern/cycles/kernel/osl/osl_services.cpp b/intern/cycles/kernel/osl/osl_services.cpp
index d5edd04d8a5..8f437755bb9 100644
--- a/intern/cycles/kernel/osl/osl_services.cpp
+++ b/intern/cycles/kernel/osl/osl_services.cpp
@@ -85,6 +85,7 @@ ustring OSLRenderServices::u_curve_tangent_normal("geom:curve_tangent_normal");
 #endif
 ustring OSLRenderServices::u_path_ray_length("path:ray_length");
 ustring OSLRenderServices::u_path_ray_depth("path:ray_depth");
+ustring OSLRenderServices::u_path_transparent_depth("path:transparent_depth");
 ustring OSLRenderServices::u_trace("trace");
 ustring OSLRenderServices::u_hit("hit");
 ustring OSLRenderServices::u_hitdist("hitdist");
@@ -701,6 +702,11 @@ bool OSLRenderServices::get_background_attribute(KernelGlobals *kg, ShaderData *
 		int f = sd->ray_depth;
 		return set_attribute_int(f, type, derivatives, val);
 	}
+	else if (name == u_path_transparent_depth) {
+		/* Ray Depth */
+		int f = sd->transparent_depth;
+		return set_attribute_int(f, type, derivatives, val);
+	}
 	else if (name == u_ndc) {
 		/* NDC coordinates with special exception for otho */
 		OSLThreadData *tdata = kg->osl_tdata;
@@ -1031,8 +1037,9 @@ bool OSLRenderServices::getmessage(OSL::ShaderGlobals *sg, ustring source, ustri
 					/* lazy shader data setup */
 					ShaderData *original_sd = (ShaderData *)(sg->renderstate);
 					int bounce = original_sd->ray_depth + 1;
+					int transparent_bounce = original_sd->transparent_depth;
 
-					shader_setup_from_ray(kg, sd, &tracedata->isect, &tracedata->ray, bounce);
+					shader_setup_from_ray(kg, sd, &tracedata->isect, &tracedata->ray, bounce, transparent_bounce);
 					tracedata->setup = true;
 				}
 
diff --git a/intern/cycles/kernel/osl/osl_services.h b/intern/cycles/kernel/osl/osl_services.h
index 479b6da1afb..c3ea12253e9 100644
--- a/intern/cycles/kernel/osl/osl_services.h
+++ b/intern/cycles/kernel/osl/osl_services.h
@@ -144,6 +144,7 @@ public:
 	static ustring u_curve_tangent_normal;
 	static ustring u_path_ray_length;
 	static ustring u_path_ray_depth;
+	static ustring u_path_transparent_depth;
 	static ustring u_trace;
 	static ustring u_hit;
 	static ustring u_hitdist;
diff --git a/intern/cycles/kernel/shaders/node_light_path.osl b/intern/cycles/kernel/shaders/node_light_path.osl
index 599c7f5a262..95fbcabf917 100644
--- a/intern/cycles/kernel/shaders/node_light_path.osl
+++ b/intern/cycles/kernel/shaders/node_light_path.osl
@@ -26,7 +26,8 @@ shader node_light_path(
 	output float IsTransmissionRay = 0.0,
 	output float IsVolumeScatterRay = 0.0,
 	output float RayLength = 0.0,
-	output float RayDepth = 0.0)
+	output float RayDepth = 0.0,
+	output float TransparentDepth = 0.0)
 {
 	IsCameraRay = raytype("camera");
 	IsShadowRay = raytype("shadow");
@@ -42,5 +43,9 @@ shader node_light_path(
 	int ray_depth;
 	getattribute("path:ray_depth", ray_depth);
 	RayDepth = (float)ray_depth;
+
+	int transparent_depth;
+	getattribute("path:transparent_depth", transparent_depth);
+	TransparentDepth = (float)transparent_depth;
 }
 
diff --git a/intern/cycles/kernel/svm/svm_light_path.h b/intern/cycles/kernel/svm/svm_light_path.h
index 8968146c5e2..da544c63ae0 100644
--- a/intern/cycles/kernel/svm/svm_light_path.h
+++ b/intern/cycles/kernel/svm/svm_light_path.h
@@ -34,6 +34,7 @@ ccl_device void svm_node_light_path(ShaderData *sd, float *stack, uint type, uin
 		case NODE_LP_backfacing: info = (sd->flag & SD_BACKFACING)? 1.0f: 0.0f; break;
 		case NODE_LP_ray_length: info = sd->ray_length; break;
 		case NODE_LP_ray_depth: info = (float)sd->ray_depth; break;
+		case NODE_LP_ray_transparent: info = sd->transparent_depth; break;
 	}
 
 	stack_store_float(stack, out_offset, info);
diff --git a/intern/cycles/kernel/svm/svm_types.h b/intern/cycles/kernel/svm/svm_types.h
index 866208106dc..86bb3f048dc 100644
--- a/intern/cycles/kernel/svm/svm_types.h
+++ b/intern/cycles/kernel/svm/svm_types.h
@@ -160,7 +160,8 @@ typedef enum NodeLightPath {
 	NODE_LP_volume_scatter,
 	NODE_LP_backfacing,
 	NODE_LP_ray_length,
-	NODE_LP_ray_depth
+	NODE_LP_ray_depth,
+	NODE_LP_ray_transparent
 } NodeLightPath;
 
 typedef enum NodeLightFalloff {
diff --git a/intern/cycles/render/nodes.cpp b/intern/cycles/render/nodes.cpp
index 87affcbb49d..1d59b21d1c5 100644
--- a/intern/cycles/render/nodes.cpp
+++ b/intern/cycles/render/nodes.cpp
@@ -2419,6 +2419,7 @@ LightPathNode::LightPathNode()
 	add_output("Is Volume Scatter Ray", SHADER_SOCKET_FLOAT);
 	add_output("Ray Length", SHADER_SOCKET_FLOAT);
 	add_output("Ray Depth", SHADER_SOCKET_FLOAT);
+	add_output("Transparent Depth", SHADER_SOCKET_FLOAT);
 }
 
 void LightPathNode::compile(SVMCompiler& compiler)
@@ -2486,6 +2487,11 @@ void LightPathNode::compile(SVMCompiler& compiler)
 		compiler.add_node(NODE_LIGHT_PATH, NODE_LP_ray_depth, out->stack_offset);
 	}
 
+	out = output("Transparent Depth");
+	if(!out->links.empty()) {
+		compiler.stack_assign(out);
+		compiler.add_node(NODE_LIGHT_PATH, NODE_LP_ray_transparent, out->stack_offset);
+	}
 }
 
 void LightPathNode::compile(OSLCompiler& compiler)
diff --git a/source/blender/nodes/shader/nodes/node_shader_light_path.c b/source/blender/nodes/shader/nodes/node_shader_light_path.c
index 9d769b284b1..023c6ea02a9 100644
--- a/source/blender/nodes/shader/nodes/node_shader_light_path.c
+++ b/source/blender/nodes/shader/nodes/node_shader_light_path.c
@@ -39,6 +39,7 @@ static bNodeSocketTemplate sh_node_light_path_out[] = {
 	{	SOCK_FLOAT, 0, N_("Is Transmission Ray"),	0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f},
 	{	SOCK_FLOAT, 0, N_("Ray Length"),			0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f},
 	{	SOCK_FLOAT, 0, N_("Ray Depth"),				0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f},
+	{	SOCK_FLOAT, 0, N_("Transparent Depth"),		0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f},
 	{	-1, 0, ""	}
 };