Cycles: Implement denoising option for reducing noise in the rendered image

This commit contains the first part of the new Cycles denoising option,
which filters the resulting image using information gathered during rendering
to get rid of noise while preserving visual features as well as possible.

To use the option, enable it in the render layer options. The default settings
fit a wide range of scenes, but the user can tweak individual settings to
control the tradeoff between a noise-free image, image details, and calculation
time.

Note that the denoiser may still change in the future and that some features
are not implemented yet. The most important missing feature is animation
denoising, which uses information from multiple frames at once to produce a
flicker-free and smoother result. These features will be added in the future.

Finally, thanks to all the people who supported this project:

- Google (through the GSoC) and Theory Studios for sponsoring the development
- The authors of the papers I used for implementing the denoiser (more details
  on them will be included in the technical docs)
- The other Cycles devs for feedback on the code, especially Sergey for
  mentoring the GSoC project and Brecht for the code review!
- And of course the users who helped with testing, reported bugs and things
  that could and/or should work better!

1 files changed, 80 insertions, 18 deletions

diff --git a/intern/cycles/kernel/kernel_accumulate.h b/intern/cycles/kernel/kernel_accumulate.h
index 823d30dde78..06728415c15 100644
--- a/intern/cycles/kernel/kernel_accumulate.h
+++ b/intern/cycles/kernel/kernel_accumulate.h
@@ -222,6 +222,12 @@ ccl_device_inline void path_radiance_init(PathRadiance *L, int use_light_pass)
 	L->path_total_shaded = make_float3(0.0f, 0.0f, 0.0f);
 	L->shadow_color = make_float3(0.0f, 0.0f, 0.0f);
 #endif
+
+#ifdef __DENOISING_FEATURES__
+	L->denoising_normal = make_float3(0.0f, 0.0f, 0.0f);
+	L->denoising_albedo = make_float3(0.0f, 0.0f, 0.0f);
+	L->denoising_depth = 0.0f;
+#endif  /* __DENOISING_FEATURES__ */
 }
 
 ccl_device_inline void path_radiance_bsdf_bounce(PathRadiance *L, ccl_addr_space float3 *throughput,
@@ -277,15 +283,15 @@ ccl_device_inline void path_radiance_accum_emission(PathRadiance *L, float3 thro
 }
 
 ccl_device_inline void path_radiance_accum_ao(PathRadiance *L,
+                                              ccl_addr_space PathState *state,
                                               float3 throughput,
                                               float3 alpha,
                                               float3 bsdf,
-                                              float3 ao,
-                                              int bounce)
+                                              float3 ao)
 {
 #ifdef __PASSES__
 	if(L->use_light_pass) {
-		if(bounce == 0) {
+		if(state->bounce == 0) {
 			/* directly visible lighting */
 			L->direct_diffuse += throughput*bsdf*ao;
 			L->ao += alpha*throughput*ao;
@@ -302,31 +308,43 @@ ccl_device_inline void path_radiance_accum_ao(PathRadiance *L,
 	}
 
 #ifdef __SHADOW_TRICKS__
-	float3 light = throughput * bsdf;
-	L->path_total += light;
-	L->path_total_shaded += ao * light;
+	if(state->flag & PATH_RAY_STORE_SHADOW_INFO) {
+		float3 light = throughput * bsdf;
+		L->path_total += light;
+		L->path_total_shaded += ao * light;
+	}
 #endif
 }
 
 ccl_device_inline void path_radiance_accum_total_ao(
         PathRadiance *L,
+        ccl_addr_space PathState *state,
         float3 throughput,
         float3 bsdf)
 {
 #ifdef __SHADOW_TRICKS__
-	L->path_total += throughput * bsdf;
+	if(state->flag & PATH_RAY_STORE_SHADOW_INFO) {
+		L->path_total += throughput * bsdf;
+	}
 #else
 	(void) L;
+	(void) state;
 	(void) throughput;
 	(void) bsdf;
 #endif
 }
 
-ccl_device_inline void path_radiance_accum_light(PathRadiance *L, float3 throughput, BsdfEval *bsdf_eval, float3 shadow, float shadow_fac, int bounce, bool is_lamp)
+ccl_device_inline void path_radiance_accum_light(PathRadiance *L,
+                                                 ccl_addr_space PathState *state,
+                                                 float3 throughput,
+                                                 BsdfEval *bsdf_eval,
+                                                 float3 shadow,
+                                                 float shadow_fac,
+                                                 bool is_lamp)
 {
 #ifdef __PASSES__
 	if(L->use_light_pass) {
-		if(bounce == 0) {
+		if(state->bounce == 0) {
 			/* directly visible lighting */
 			L->direct_diffuse += throughput*bsdf_eval->diffuse*shadow;
 			L->direct_glossy += throughput*bsdf_eval->glossy*shadow;
@@ -352,21 +370,27 @@ ccl_device_inline void path_radiance_accum_light(PathRadiance *L, float3 through
 	}
 
 #ifdef __SHADOW_TRICKS__
-	float3 light = throughput * bsdf_eval->sum_no_mis;
-	L->path_total += light;
-	L->path_total_shaded += shadow * light;
+	if(state->flag & PATH_RAY_STORE_SHADOW_INFO) {
+		float3 light = throughput * bsdf_eval->sum_no_mis;
+		L->path_total += light;
+		L->path_total_shaded += shadow * light;
+	}
 #endif
 }
 
 ccl_device_inline void path_radiance_accum_total_light(
         PathRadiance *L,
+        ccl_addr_space PathState *state,
         float3 throughput,
         const BsdfEval *bsdf_eval)
 {
 #ifdef __SHADOW_TRICKS__
-	L->path_total += throughput * bsdf_eval->sum_no_mis;
+	if(state->flag & PATH_RAY_STORE_SHADOW_INFO) {
+		L->path_total += throughput * bsdf_eval->sum_no_mis;
+	}
 #else
 	(void) L;
+	(void) state;
 	(void) throughput;
 	(void) bsdf_eval;
 #endif
@@ -393,11 +417,17 @@ ccl_device_inline void path_radiance_accum_background(PathRadiance *L,
 	}
 
 #ifdef __SHADOW_TRICKS__
-	L->path_total += throughput * value;
-	if(state->flag & PATH_RAY_SHADOW_CATCHER_ONLY) {
-		L->path_total_shaded += throughput * value;
+	if(state->flag & PATH_RAY_STORE_SHADOW_INFO) {
+		L->path_total += throughput * value;
+		if(state->flag & PATH_RAY_SHADOW_CATCHER_ONLY) {
+			L->path_total_shaded += throughput * value;
+		}
 	}
 #endif
+
+#ifdef __DENOISING_FEATURES__
+	L->denoising_albedo += state->denoising_feature_weight * value;
+#endif  /* __DENOISING_FEATURES__ */
 }
 
 ccl_device_inline void path_radiance_sum_indirect(PathRadiance *L)
@@ -555,6 +585,38 @@ ccl_device_inline float3 path_radiance_clamp_and_sum(KernelGlobals *kg, PathRadi
 	return L_sum;
 }
 
+ccl_device_inline void path_radiance_split_denoising(KernelGlobals *kg, PathRadiance *L, float3 *noisy, float3 *clean)
+{
+#ifdef __PASSES__
+	kernel_assert(L->use_light_pass);
+
+	*clean = L->emission + L->background;
+	*noisy = L->direct_scatter + L->indirect_scatter;
+
+#  define ADD_COMPONENT(flag, component)     \
+	if(kernel_data.film.denoising_flags & flag) \
+		*clean += component;                 \
+	else                                     \
+		*noisy += component;
+
+	ADD_COMPONENT(DENOISING_CLEAN_DIFFUSE_DIR,      L->direct_diffuse);
+	ADD_COMPONENT(DENOISING_CLEAN_DIFFUSE_IND,      L->indirect_diffuse);
+	ADD_COMPONENT(DENOISING_CLEAN_GLOSSY_DIR,       L->direct_glossy);
+	ADD_COMPONENT(DENOISING_CLEAN_GLOSSY_IND,       L->indirect_glossy);
+	ADD_COMPONENT(DENOISING_CLEAN_TRANSMISSION_DIR, L->direct_transmission);
+	ADD_COMPONENT(DENOISING_CLEAN_TRANSMISSION_IND, L->indirect_transmission);
+	ADD_COMPONENT(DENOISING_CLEAN_SUBSURFACE_DIR,   L->direct_subsurface);
+	ADD_COMPONENT(DENOISING_CLEAN_SUBSURFACE_IND,   L->indirect_subsurface);
+#  undef ADD_COMPONENT
+#else
+	*noisy = L->emission;
+	*clean = make_float3(0.0f, 0.0f, 0.0f);
+#endif
+
+	*noisy = ensure_finite3(*noisy);
+	*clean = ensure_finite3(*clean);
+}
+
 ccl_device_inline void path_radiance_accum_sample(PathRadiance *L, PathRadiance *L_sample, int num_samples)
 {
 	float fac = 1.0f/num_samples;
@@ -595,12 +657,12 @@ ccl_device_inline float path_radiance_sum_shadow(const PathRadiance *L)
 /* Calculate final light sum and transparency for shadow catcher object. */
 ccl_device_inline float3 path_radiance_sum_shadowcatcher(KernelGlobals *kg,
                                                          const PathRadiance *L,
-                                                         ccl_addr_space float* L_transparent)
+                                                         float* alpha)
 {
 	const float shadow = path_radiance_sum_shadow(L);
 	float3 L_sum;
 	if(kernel_data.background.transparent) {
-		*L_transparent = shadow;
+		*alpha = 1.0f-shadow;
 		L_sum = make_float3(0.0f, 0.0f, 0.0f);
 	}
 	else {