Cycles: Add support for debug passes

Currently only summed number of traversal steps and intersections used by the
camera ray intersection pass is implemented, but in the future we will support
more debug passes which would help checking what things makes the scene slow.
Example of such extra passes could be number of bounces, time spent on the
shader tree evaluation and so.

Implementation from the Cycles side is pretty much straightforward, could only
mention here that it's a build-time option disabled by default.

From the blender side it's implemented as a PASS_DEBUG with several subtypes
possible. This way we don't need to create an extra DNA pass type for each of
the debug passes, saving us a bits.

Reviewers: campbellbarton

Reviewed By: campbellbarton

Differential Revision: https://developer.blender.org/D813

21 files changed, 223 insertions, 2 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b3918214f8c..3222feb4093 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -282,6 +282,9 @@ set(CYCLES_CUDA_BINARIES_ARCH sm_20 sm_21 sm_30 sm_35 sm_50 CACHE STRING "CUDA a
 mark_as_advanced(CYCLES_CUDA_BINARIES_ARCH)
 unset(PLATFORM_DEFAULT)
 option(WITH_CYCLES_LOGGING	"Build cycles with logging support" OFF)
+option(WITH_CYCLES_DEBUG	"Build cycles with with extra debug capabilties" OFF)
+mark_as_advanced(WITH_CYCLES_LOGGING)
+mark_as_advanced(WITH_CYCLES_DEBUG)
 
 # LLVM
 option(WITH_LLVM					"Use LLVM" OFF)
diff --git a/build_files/scons/tools/btools.py b/build_files/scons/tools/btools.py
index 35607e3acd0..4106c037ecd 100644
--- a/build_files/scons/tools/btools.py
+++ b/build_files/scons/tools/btools.py
@@ -192,7 +192,8 @@ def validate_arguments(args, bc):
             'BF_DEBUG_CFLAGS', 'BF_DEBUG_CCFLAGS', 'BF_DEBUG_CXXFLAGS',
             'C_WARN', 'CC_WARN', 'CXX_WARN',
             'LLIBS', 'PLATFORM_LINKFLAGS', 'MACOSX_ARCHITECTURE', 'MACOSX_SDK', 'XCODE_CUR_VER', 'C_COMPILER_ID',
-            'BF_CYCLES_CUDA_BINARIES_ARCH', 'BF_PROGRAM_LINKFLAGS', 'MACOSX_DEPLOYMENT_TARGET'
+            'BF_CYCLES_CUDA_BINARIES_ARCH', 'BF_PROGRAM_LINKFLAGS', 'MACOSX_DEPLOYMENT_TARGET',
+            'WITH_BF_CYCLES_DEBUG'
     ]
 
 
@@ -586,6 +587,7 @@ def read_opts(env, cfg, args):
         ('BF_CYCLES_CUDA_NVCC', 'CUDA nvcc compiler path', ''),
         ('BF_CYCLES_CUDA_ENV', 'preset environement nvcc will execute in', ''),
         ('BF_CYCLES_CUDA_BINARIES_ARCH', 'CUDA architectures to compile binaries for', []),
+        (BoolVariable('WITH_BF_CYCLES_DEBUG', 'Build Cycles engine with extra debugging capabilities', False)),
 
         (BoolVariable('WITH_BF_OIIO', 'Build with OpenImageIO', False)),
         (BoolVariable('WITH_BF_STATICOIIO', 'Statically link to OpenImageIO', False)),
diff --git a/intern/cycles/CMakeLists.txt b/intern/cycles/CMakeLists.txt
index bfd29dcf606..981499b3a91 100644
--- a/intern/cycles/CMakeLists.txt
+++ b/intern/cycles/CMakeLists.txt
@@ -128,6 +128,7 @@ add_definitions(
 	-DWITH_MULTI
 )
 
+# Logging capabilities using GLog library.
 if(WITH_CYCLES_LOGGING)
 	add_definitions(-DWITH_CYCLES_LOGGING)
 	add_definitions(-DGOOGLE_GLOG_DLL_DECL=)
@@ -146,6 +147,11 @@ if(WITH_CYCLES_LOGGING)
 	endif()
 endif()
 
+# Debugging capabilities (debug passes etc).
+if(WITH_CYCLES_DEBUG)
+	add_definitions(-DWITH_CYCLES_DEBUG)
+endif()
+
 include_directories(
 	SYSTEM
 	${BOOST_INCLUDE_DIR}
diff --git a/intern/cycles/SConscript b/intern/cycles/SConscript
index a6c947bfca8..594b43c88b2 100644
--- a/intern/cycles/SConscript
+++ b/intern/cycles/SConscript
@@ -59,6 +59,9 @@ if env['WITH_BF_CYCLES_OSL']:
     defs.append('OSL_STATIC_LIBRARY')
     incs.append(cycles['BF_OSL_INC'])
 
+if env['WITH_BF_CYCLES_DEBUG']:
+    defs.append('WITH_CYCLES_DEBUG')
+
 incs.extend('. bvh render device kernel kernel/osl kernel/svm util subd'.split())
 incs.extend('#intern/guardedalloc #source/blender/makesrna #source/blender/makesdna #source/blender/blenlib'.split())
 incs.extend('#source/blender/blenloader ../../source/blender/makesrna/intern'.split())
diff --git a/intern/cycles/blender/blender_session.cpp b/intern/cycles/blender/blender_session.cpp
index 4ff3d89f9f1..0610c3f6579 100644
--- a/intern/cycles/blender/blender_session.cpp
+++ b/intern/cycles/blender/blender_session.cpp
@@ -261,6 +261,14 @@ static PassType get_pass_type(BL::RenderPass b_pass)
 		case BL::RenderPass::type_SPECULAR:
 		case BL::RenderPass::type_REFLECTION:
 			return PASS_NONE;
+#ifdef WITH_CYCLES_DEBUG
+		case BL::RenderPass::type_DEBUG:
+		{
+			if(b_pass.debug_type() == BL::RenderPass::debug_type_BVH_TRAVERSAL_STEPS)
+				return PASS_BVH_TRAVERSAL_STEPS;
+			break;
+		}
+#endif
 	}
 	
 	return PASS_NONE;
@@ -423,6 +431,9 @@ void BlenderSession::render()
 		/* add passes */
 		vector<Pass> passes;
 		Pass::add(PASS_COMBINED, passes);
+#ifdef WITH_CYCLES_DEBUG
+		Pass::add(PASS_BVH_TRAVERSAL_STEPS, passes);
+#endif
 
 		if(session_params.device.advanced_shading) {
 
diff --git a/intern/cycles/kernel/CMakeLists.txt b/intern/cycles/kernel/CMakeLists.txt
index 2d2eaa81211..c5ea3abc567 100644
--- a/intern/cycles/kernel/CMakeLists.txt
+++ b/intern/cycles/kernel/CMakeLists.txt
@@ -24,6 +24,7 @@ set(SRC_HEADERS
 	kernel_compat_cpu.h
 	kernel_compat_cuda.h
 	kernel_compat_opencl.h
+	kernel_debug.h
 	kernel_differential.h
 	kernel_emission.h
 	kernel_film.h
diff --git a/intern/cycles/kernel/geom/geom_bvh_traversal.h b/intern/cycles/kernel/geom/geom_bvh_traversal.h
index e39228c33de..eed54a4d00d 100644
--- a/intern/cycles/kernel/geom/geom_bvh_traversal.h
+++ b/intern/cycles/kernel/geom/geom_bvh_traversal.h
@@ -68,6 +68,10 @@ ccl_device bool BVH_FUNCTION_NAME
 	isect->u = 0.0f;
 	isect->v = 0.0f;
 
+#if defined(__KERNEL_DEBUG__)
+	isect->num_traversal_steps = 0;
+#endif
+
 #if defined(__KERNEL_SSE2__)
 	const shuffle_swap_t shuf_identity = shuffle_swap_identity();
 	const shuffle_swap_t shuf_swap = shuffle_swap_swap();
@@ -226,6 +230,10 @@ ccl_device bool BVH_FUNCTION_NAME
 						--stackPtr;
 					}
 				}
+
+#if defined(__KERNEL_DEBUG__)
+				isect->num_traversal_steps++;
+#endif
 			}
 
 			/* if node is leaf, fetch triangle list */
@@ -274,6 +282,10 @@ ccl_device bool BVH_FUNCTION_NAME
 							}
 						}
 
+#if defined(__KERNEL_DEBUG__)
+						isect->num_traversal_steps++;
+#endif
+
 						/* shadow ray early termination */
 #if defined(__KERNEL_SSE2__)
 						if(hit) {
diff --git a/intern/cycles/kernel/kernel_debug.h b/intern/cycles/kernel/kernel_debug.h
new file mode 100644
index 00000000000..81ce1e76420
--- /dev/null
+++ b/intern/cycles/kernel/kernel_debug.h
@@ -0,0 +1,35 @@
+/*
+ * Copyright 2011-2014 Blender Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License
+ */
+
+CCL_NAMESPACE_BEGIN
+
+ccl_device_inline void debug_data_init(DebugData *debug_data)
+{
+	debug_data->num_bvh_traversal_steps = 0;
+}
+
+ccl_device_inline void kernel_write_debug_passes(KernelGlobals *kg,
+                                                 ccl_global float *buffer,
+                                                 PathState *state,
+                                                 DebugData *debug_data,
+                                                 int sample)
+{
+	kernel_write_pass_float(buffer + kernel_data.film.pass_bvh_traversal_steps,
+	                        sample,
+	                        debug_data->num_bvh_traversal_steps);
+}
+
+CCL_NAMESPACE_END
diff --git a/intern/cycles/kernel/kernel_path.h b/intern/cycles/kernel/kernel_path.h
index e68a8370012..0e07d8a95f8 100644
--- a/intern/cycles/kernel/kernel_path.h
+++ b/intern/cycles/kernel/kernel_path.h
@@ -45,6 +45,10 @@
 #include "kernel_path_surface.h"
 #include "kernel_path_volume.h"
 
+#ifdef __KERNEL_DEBUG__
+#  include "kernel_debug.h"
+#endif
+
 CCL_NAMESPACE_BEGIN
 
 ccl_device void kernel_path_indirect(KernelGlobals *kg, RNG *rng, Ray ray,
@@ -473,6 +477,11 @@ ccl_device float4 kernel_path_integrate(KernelGlobals *kg, RNG *rng, int sample,
 	PathState state;
 	path_state_init(kg, &state, rng, sample, &ray);
 
+#ifdef __KERNEL_DEBUG__
+	DebugData debug_data;
+	debug_data_init(&debug_data);
+#endif
+
 	/* path iteration */
 	for(;;) {
 		/* intersect scene */
@@ -499,6 +508,12 @@ ccl_device float4 kernel_path_integrate(KernelGlobals *kg, RNG *rng, int sample,
 		bool hit = scene_intersect(kg, &ray, visibility, &isect, NULL, 0.0f, 0.0f);
 #endif
 
+#ifdef __KERNEL_DEBUG__
+		if(state.flag & PATH_RAY_CAMERA) {
+			debug_data.num_bvh_traversal_steps += isect.num_traversal_steps;
+		}
+#endif
+
 #ifdef __LAMP_MIS__
 		if(kernel_data.integrator.use_lamp_mis && !(state.flag & PATH_RAY_CAMERA)) {
 			/* ray starting from previous non-transparent bounce */
@@ -719,6 +734,10 @@ ccl_device float4 kernel_path_integrate(KernelGlobals *kg, RNG *rng, int sample,
 
 	kernel_write_light_passes(kg, buffer, &L, sample);
 
+#ifdef __KERNEL_DEBUG__
+	kernel_write_debug_passes(kg, buffer, &state, &debug_data, sample);
+#endif
+
 	return make_float4(L_sum.x, L_sum.y, L_sum.z, 1.0f - L_transparent);
 }
 
@@ -864,6 +883,11 @@ ccl_device float4 kernel_branched_path_integrate(KernelGlobals *kg, RNG *rng, in
 	PathState state;
 	path_state_init(kg, &state, rng, sample, &ray);
 
+#ifdef __KERNEL_DEBUG__
+	DebugData debug_data;
+	debug_data_init(&debug_data);
+#endif
+
 	for(;;) {
 		/* intersect scene */
 		Intersection isect;
@@ -889,6 +913,12 @@ ccl_device float4 kernel_branched_path_integrate(KernelGlobals *kg, RNG *rng, in
 		bool hit = scene_intersect(kg, &ray, visibility, &isect, NULL, 0.0f, 0.0f);
 #endif
 
+#ifdef __KERNEL_DEBUG__
+		if(state.flag & PATH_RAY_CAMERA) {
+			debug_data.num_bvh_traversal_steps += isect.num_traversal_steps;
+		}
+#endif
+
 #ifdef __VOLUME__
 		/* volume attenuation, emission, scatter */
 		if(state.volume_stack[0].shader != SHADER_NONE) {
@@ -1144,6 +1174,10 @@ ccl_device float4 kernel_branched_path_integrate(KernelGlobals *kg, RNG *rng, in
 
 	kernel_write_light_passes(kg, buffer, &L, sample);
 
+#ifdef __KERNEL_DEBUG__
+	kernel_write_debug_passes(kg, buffer, &state, &debug_data, sample);
+#endif
+
 	return make_float4(L_sum.x, L_sum.y, L_sum.z, 1.0f - L_transparent);
 }
 
diff --git a/intern/cycles/kernel/kernel_types.h b/intern/cycles/kernel/kernel_types.h
index 2fe1cd87072..43becf14825 100644
--- a/intern/cycles/kernel/kernel_types.h
+++ b/intern/cycles/kernel/kernel_types.h
@@ -157,6 +157,10 @@ CCL_NAMESPACE_BEGIN
 #define __HAIR__
 #endif
 
+#ifdef WITH_CYCLES_DEBUG
+#  define __KERNEL_DEBUG__
+#endif
+
 /* Random Numbers */
 
 typedef uint RNG;
@@ -313,6 +317,9 @@ typedef enum PassType {
 	PASS_SUBSURFACE_INDIRECT = 8388608,
 	PASS_SUBSURFACE_COLOR = 16777216,
 	PASS_LIGHT = 33554432, /* no real pass, used to force use_light_pass */
+#ifdef __KERNEL_DEBUG__
+	PASS_BVH_TRAVERSAL_STEPS = 67108864,
+#endif
 } PassType;
 
 #define PASS_ALL (~0)
@@ -453,6 +460,10 @@ typedef struct Intersection {
 	int prim;
 	int object;
 	int type;
+
+#ifdef __KERNEL_DEBUG__
+	int num_traversal_steps;
+#endif
 } Intersection;
 
 /* Primitives */
@@ -850,6 +861,11 @@ typedef struct KernelFilm {
 	float mist_start;
 	float mist_inv_depth;
 	float mist_falloff;
+
+#ifdef __KERNEL_DEBUG__
+	int pass_bvh_traversal_steps;
+	int pad[3];
+#endif
 } KernelFilm;
 
 typedef struct KernelBackground {
@@ -976,6 +992,14 @@ typedef struct KernelData {
 	KernelTables tables;
 } KernelData;
 
+#ifdef __KERNEL_DEBUG__
+typedef struct DebugData {
+	// Total number of BVH node travesal steps and primitives intersections
+	// for the camera rays.
+	int num_bvh_traversal_steps;
+} DebugData;
+#endif
+
 CCL_NAMESPACE_END
 
 #endif /*  __KERNEL_TYPES_H__ */
diff --git a/intern/cycles/render/buffers.cpp b/intern/cycles/render/buffers.cpp
index fc65922fc87..756e16b38b5 100644
--- a/intern/cycles/render/buffers.cpp
+++ b/intern/cycles/render/buffers.cpp
@@ -190,6 +190,14 @@ bool RenderBuffers::get_pass_rect(PassType type, float exposure, int sample, int
 					pixels[0] = clamp(f*scale_exposure, 0.0f, 1.0f);
 				}
 			}
+#ifdef WITH_CYCLES_DEBUG
+			else if(type == PASS_BVH_TRAVERSAL_STEPS) {
+				for(int i = 0; i < size; i++, in += pass_stride, pixels++) {
+					float f = *in;
+					pixels[0] = f;
+				}
+			}
+#endif
 			else {
 				for(int i = 0; i < size; i++, in += pass_stride, pixels++) {
 					float f = *in;
diff --git a/intern/cycles/render/film.cpp b/intern/cycles/render/film.cpp
index 09973e8bc86..19f959d4ea1 100644
--- a/intern/cycles/render/film.cpp
+++ b/intern/cycles/render/film.cpp
@@ -146,6 +146,12 @@ void Pass::add(PassType type, vector<Pass>& passes)
 		case PASS_LIGHT:
 			/* ignores */
 			break;
+#ifdef WITH_CYCLES_DEBUG
+		case PASS_BVH_TRAVERSAL_STEPS:
+			pass.components = 1;
+			pass.exposure = false;
+			break;
+#endif
 	}
 
 	passes.push_back(pass);
@@ -388,6 +394,13 @@ void Film::device_update(Device *device, DeviceScene *dscene, Scene *scene)
 			case PASS_LIGHT:
 				kfilm->use_light_pass = 1;
 				break;
+
+#ifdef WITH_CYCLES_DEBUG
+			case PASS_BVH_TRAVERSAL_STEPS:
+				kfilm->pass_bvh_traversal_steps = kfilm->pass_stride;
+				break;
+#endif
+
 			case PASS_NONE:
 				break;
 		}
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index c8b8e4d52a4..ab13c704df4 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -242,6 +242,7 @@ typedef enum ScenePassType {
 	SCE_PASS_SUBSURFACE_DIRECT        = (1 << 28),
 	SCE_PASS_SUBSURFACE_INDIRECT      = (1 << 29),
 	SCE_PASS_SUBSURFACE_COLOR         = (1 << 30),
+	SCE_PASS_DEBUG                    = (1 << 31),  /* This is a virtual pass. */
 } ScenePassType;
 
 /* note, srl->passflag is treestore element 'nr' in outliner, short still... */
diff --git a/source/blender/makesrna/SConscript b/source/blender/makesrna/SConscript
index 898881076c4..c59e17f76df 100644
--- a/source/blender/makesrna/SConscript
+++ b/source/blender/makesrna/SConscript
@@ -117,6 +117,9 @@ if env['WITH_BF_OCEANSIM']:
 if env['WITH_BF_CYCLES']:
     defs.append('WITH_CYCLES')
 
+  if env['WITH_BF_CYCLES_DEBUG']:
+      defs.append('WITH_CYCLES_DEBUG')
+
 if env['WITH_BF_SDL']:
     defs.append('WITH_SDL')
 
diff --git a/source/blender/makesrna/intern/CMakeLists.txt b/source/blender/makesrna/intern/CMakeLists.txt
index d62a2e2c76e..c5f62439b9e 100644
--- a/source/blender/makesrna/intern/CMakeLists.txt
+++ b/source/blender/makesrna/intern/CMakeLists.txt
@@ -155,6 +155,9 @@ set(INC_SYS
 
 if(WITH_CYCLES)
 	add_definitions(-DWITH_CYCLES)
+	if(WITH_CYCLES_DEBUG)
+		add_definitions(-DWITH_CYCLES_DEBUG)
+	endif()
 endif()
 
 if(WITH_PYTHON)
diff --git a/source/blender/makesrna/intern/SConscript b/source/blender/makesrna/intern/SConscript
index 179a332336e..9fda79feb74 100644
--- a/source/blender/makesrna/intern/SConscript
+++ b/source/blender/makesrna/intern/SConscript
@@ -140,6 +140,8 @@ if env['WITH_BF_COLLADA']:
 
 if env['WITH_BF_CYCLES']:
     defs.append('WITH_CYCLES')
+    if env['WITH_BF_CYCLES_DEBUG']:
+        defs.append('WITH_CYCLES_DEBUG')
 
 if env['WITH_BF_FREESTYLE']:
     defs.append('WITH_FREESTYLE')
diff --git a/source/blender/makesrna/intern/rna_render.c b/source/blender/makesrna/intern/rna_render.c
index 284377d34f9..c5750f56d28 100644
--- a/source/blender/makesrna/intern/rna_render.c
+++ b/source/blender/makesrna/intern/rna_render.c
@@ -71,6 +71,9 @@ EnumPropertyItem render_pass_type_items[] = {
 	{SCE_PASS_SUBSURFACE_DIRECT, "SUBSURFACE_DIRECT", 0, "Subsurface Direct", ""},
 	{SCE_PASS_SUBSURFACE_INDIRECT, "SUBSURFACE_INDIRECT", 0, "Subsurface Indirect", ""},
 	{SCE_PASS_SUBSURFACE_COLOR, "SUBSURFACE_COLOR", 0, "Subsurface Color", ""},
+#ifdef WITH_CYCLES_DEBUG
+	{SCE_PASS_DEBUG, "DEBUG", 0, "Pass used for render engine debugging", ""},
+#endif
 	{0, NULL, 0, NULL, NULL}
 };
 
@@ -683,6 +686,10 @@ static void rna_def_render_pass(BlenderRNA *brna)
 	StructRNA *srna;
 	PropertyRNA *prop;
 
+	static EnumPropertyItem render_pass_debug_type_items[] = {
+		{RENDER_PASS_DEBUG_BVH_TRAVERSAL_STEPS, "BVH_TRAVERSAL_STEPS", 0, "BVH Traversal Steps", ""},
+	};
+
 	srna = RNA_def_struct(brna, "RenderPass", NULL);
 	RNA_def_struct_ui_text(srna, "Render Pass", "");
 
@@ -712,6 +719,11 @@ static void rna_def_render_pass(BlenderRNA *brna)
 	RNA_def_property_dynamic_array_funcs(prop, "rna_RenderPass_rect_get_length");
 	RNA_def_property_float_funcs(prop, "rna_RenderPass_rect_get", "rna_RenderPass_rect_set", NULL);
 
+	prop = RNA_def_property(srna, "debug_type", PROP_ENUM, PROP_NONE);
+	RNA_def_property_enum_sdna(prop, NULL, "debug_type");
+	RNA_def_property_enum_items(prop, render_pass_debug_type_items);
+	RNA_def_property_clear_flag(prop, PROP_EDITABLE);
+
 	RNA_define_verify_sdna(1);
 }
 
diff --git a/source/blender/render/CMakeLists.txt b/source/blender/render/CMakeLists.txt
index 8e326e770fc..e516c954737 100644
--- a/source/blender/render/CMakeLists.txt
+++ b/source/blender/render/CMakeLists.txt
@@ -162,6 +162,10 @@ if(WITH_INTERNATIONAL)
 	add_definitions(-DWITH_INTERNATIONAL)
 endif()
 
+if(WITH_CYCLES AND WITH_CYCLES_DEBUG)
+	add_definitions(-DWITH_CYCLES_DEBUG)
+endif()
+
 if(APPLE)
 	# SSE math is enabled by default on x86_64
 	if(CMAKE_OSX_ARCHITECTURES MATCHES "i386")
diff --git a/source/blender/render/SConscript b/source/blender/render/SConscript
index 297e4fcecd4..297debabcb4 100644
--- a/source/blender/render/SConscript
+++ b/source/blender/render/SConscript
@@ -103,6 +103,9 @@ if env['WITH_BF_GAMEENGINE']:
 if env['WITH_BF_INTERNATIONAL']:
     defs.append('WITH_INTERNATIONAL')
 
+if env['WITH_BF_CYCLES'] and env['WITH_VF_CYCLES_DEBUG']:
+    defs.append('WITH_CYCLES_DEBUG')
+
 if env['OURPLATFORM'] in ('win32-vc', 'win32-mingw', 'linuxcross', 'win64-vc', 'win64-mingw'):
     incs += ' ' + env['BF_PTHREADS_INC']
 
diff --git a/source/blender/render/extern/include/RE_pipeline.h b/source/blender/render/extern/include/RE_pipeline.h
index 3b54de4c943..61795c2c173 100644
--- a/source/blender/render/extern/include/RE_pipeline.h
+++ b/source/blender/render/extern/include/RE_pipeline.h
@@ -72,8 +72,13 @@ typedef struct RenderPass {
 	char chan_id[8];	/* amount defined in openexr_multi.h */
 	float *rect;
 	int rectx, recty;
+	int debug_type;
 } RenderPass;
 
+enum {
+	RENDER_PASS_DEBUG_BVH_TRAVERSAL_STEPS = 0,
+};
+
 /* a renderlayer is a full image, but with all passes and samples */
 /* size of the rects is defined in RenderResult */
 /* after render, the Combined pass is in rectf, for renderlayers read from files it is a real pass */
diff --git a/source/blender/render/intern/source/render_result.c b/source/blender/render/intern/source/render_result.c
index d8410fbe257..24797521435 100644
--- a/source/blender/render/intern/source/render_result.c
+++ b/source/blender/render/intern/source/render_result.c
@@ -48,6 +48,9 @@
 #include "BKE_global.h"
 #include "BKE_main.h"
 #include "BKE_report.h"
+#ifdef WITH_CYCLES_DEBUG
+#  include "BKE_scene.h"
+#endif
 
 #include "IMB_imbuf.h"
 #include "IMB_imbuf_types.h"
@@ -402,7 +405,7 @@ static int passtype_from_name(const char *str)
 
 /********************************** New **************************************/
 
-static void render_layer_add_pass(RenderResult *rr, RenderLayer *rl, int channels, int passtype)
+static RenderPass *render_layer_add_pass(RenderResult *rr, RenderLayer *rl, int channels, int passtype)
 {
 	const char *typestr = get_pass_name(passtype, 0);
 	RenderPass *rpass = MEM_callocN(sizeof(RenderPass), typestr);
@@ -438,8 +441,34 @@ static void render_layer_add_pass(RenderResult *rr, RenderLayer *rl, int channel
 				rect[x] = 10e10;
 		}
 	}
+	return rpass;
 }
 
+#ifdef WITH_CYCLES_DEBUG
+static const char *debug_pass_type_name_get(int debug_type)
+{
+	switch (debug_type) {
+		case RENDER_PASS_DEBUG_BVH_TRAVERSAL_STEPS:
+			return "BVH Traversal Steps";
+	}
+	return "Unknown";
+}
+
+static RenderPass *render_layer_add_debug_pass(RenderResult *rr,
+                                               RenderLayer *rl,
+                                               int channels,
+                                               int pass_type,
+                                               int debug_type)
+{
+	RenderPass *rpass = render_layer_add_pass(rr, rl, channels, pass_type);
+	rpass->debug_type = debug_type;
+	BLI_strncpy(rpass->name,
+	            debug_pass_type_name_get(debug_type),
+	            sizeof(rpass->name));
+	return rpass;
+}
+#endif
+
 /* called by main render as well for parts */
 /* will read info from Render *re to define layers */
 /* called in threads */
@@ -578,6 +607,13 @@ RenderResult *render_result_new(Render *re, rcti *partrct, int crop, int savebuf
 			render_layer_add_pass(rr, rl, 3, SCE_PASS_SUBSURFACE_INDIRECT);
 		if (srl->passflag  & SCE_PASS_SUBSURFACE_COLOR)
 			render_layer_add_pass(rr, rl, 3, SCE_PASS_SUBSURFACE_COLOR);
+
+#ifdef WITH_CYCLES_DEBUG
+		if(BKE_scene_use_new_shading_nodes(re->scene)) {
+			render_layer_add_debug_pass(rr, rl, 1, SCE_PASS_DEBUG,
+			        RENDER_PASS_DEBUG_BVH_TRAVERSAL_STEPS);
+		}
+#endif
 	}
 	/* sss, previewrender and envmap don't do layers, so we make a default one */
 	if (BLI_listbase_is_empty(&rr->layers) && !(layername && layername[0])) {