Adaptive Sampling for Cycles.

This feature takes some inspiration from
"RenderMan: An Advanced Path Tracing Architecture for Movie Rendering" and
"A Hierarchical Automatic Stopping Condition for Monte Carlo Global Illumination"

The basic principle is as follows:
While samples are being added to a pixel, the adaptive sampler writes half
of the samples to a separate buffer. This gives it two separate estimates
of the same pixel, and by comparing their difference it estimates convergence.
Once convergence drops below a given threshold, the pixel is considered done.

When a pixel has not converged yet and needs more samples than the minimum,
its immediate neighbors are also set to take more samples. This is done in order
to more reliably detect sharp features such as caustics. A 3x3 box filter that
is run periodically over the tile buffer is used for that purpose.

After a tile has finished rendering, the values of all passes are scaled as if
they were rendered with the full number of samples. This way, any code operating
on these buffers, for example the denoiser, does not need to be changed for
per-pixel sample counts.

Reviewed By: brecht, #cycles

Differential Revision: https://developer.blender.org/D4686

1 files changed, 30 insertions, 1 deletions

diff --git a/intern/cycles/blender/blender_sync.cpp b/intern/cycles/blender/blender_sync.cpp
index 50442c6ebdc..8f00f9ccda0 100644
--- a/intern/cycles/blender/blender_sync.cpp
+++ b/intern/cycles/blender/blender_sync.cpp
@@ -296,6 +296,16 @@ void BlenderSync::sync_integrator()
   integrator->sample_all_lights_indirect = get_boolean(cscene, "sample_all_lights_indirect");
   integrator->light_sampling_threshold = get_float(cscene, "light_sampling_threshold");
 
+  if (RNA_boolean_get(&cscene, "use_adaptive_sampling")) {
+    integrator->sampling_pattern = SAMPLING_PATTERN_PMJ;
+    integrator->adaptive_min_samples = get_int(cscene, "adaptive_min_samples");
+    integrator->adaptive_threshold = get_float(cscene, "adaptive_threshold");
+  }
+  else {
+    integrator->adaptive_min_samples = INT_MAX;
+    integrator->adaptive_threshold = 0.0f;
+  }
+
   int diffuse_samples = get_int(cscene, "diffuse_samples");
   int glossy_samples = get_int(cscene, "glossy_samples");
   int transmission_samples = get_int(cscene, "transmission_samples");
@@ -312,6 +322,8 @@ void BlenderSync::sync_integrator()
     integrator->mesh_light_samples = mesh_light_samples * mesh_light_samples;
     integrator->subsurface_samples = subsurface_samples * subsurface_samples;
     integrator->volume_samples = volume_samples * volume_samples;
+    integrator->adaptive_min_samples = min(
+        integrator->adaptive_min_samples * integrator->adaptive_min_samples, INT_MAX);
   }
   else {
     integrator->diffuse_samples = diffuse_samples;
@@ -484,6 +496,8 @@ PassType BlenderSync::get_pass_type(BL::RenderPass &b_pass)
   MAP_PASS("Debug Ray Bounces", PASS_RAY_BOUNCES);
 #endif
   MAP_PASS("Debug Render Time", PASS_RENDER_TIME);
+  MAP_PASS("AdaptiveAuxBuffer", PASS_ADAPTIVE_AUX_BUFFER);
+  MAP_PASS("Debug Sample Count", PASS_SAMPLE_COUNT);
   if (string_startswith(name, cryptomatte_prefix)) {
     return PASS_CRYPTOMATTE;
   }
@@ -519,7 +533,9 @@ int BlenderSync::get_denoising_pass(BL::RenderPass &b_pass)
   return -1;
 }
 
-vector<Pass> BlenderSync::sync_render_passes(BL::RenderLayer &b_rlay, BL::ViewLayer &b_view_layer)
+vector<Pass> BlenderSync::sync_render_passes(BL::RenderLayer &b_rlay,
+                                             BL::ViewLayer &b_view_layer,
+                                             bool adaptive_sampling)
 {
   vector<Pass> passes;
 
@@ -595,6 +611,10 @@ vector<Pass> BlenderSync::sync_render_passes(BL::RenderLayer &b_rlay, BL::ViewLa
     b_engine.add_pass("Debug Render Time", 1, "X", b_view_layer.name().c_str());
     Pass::add(PASS_RENDER_TIME, passes, "Debug Render Time");
   }
+  if (get_boolean(crp, "pass_debug_sample_count")) {
+    b_engine.add_pass("Debug Sample Count", 1, "X", b_view_layer.name().c_str());
+    Pass::add(PASS_SAMPLE_COUNT, passes, "Debug Sample Count");
+  }
   if (get_boolean(crp, "use_pass_volume_direct")) {
     b_engine.add_pass("VolumeDir", 3, "RGB", b_view_layer.name().c_str());
     Pass::add(PASS_VOLUME_DIRECT, passes, "VolumeDir");
@@ -641,6 +661,13 @@ vector<Pass> BlenderSync::sync_render_passes(BL::RenderLayer &b_rlay, BL::ViewLa
                                                         CRYPT_ACCURATE);
   }
 
+  if (adaptive_sampling) {
+    Pass::add(PASS_ADAPTIVE_AUX_BUFFER, passes);
+    if (!get_boolean(crp, "pass_debug_sample_count")) {
+      Pass::add(PASS_SAMPLE_COUNT, passes);
+    }
+  }
+
   RNA_BEGIN (&crp, b_aov, "aovs") {
     bool is_color = (get_enum(b_aov, "type") == 1);
     string name = get_string(b_aov, "name");
@@ -880,6 +907,8 @@ SessionParams BlenderSync::get_session_params(BL::RenderEngine &b_engine,
   params.use_profiling = params.device.has_profiling && !b_engine.is_preview() && background &&
                          BlenderSession::print_render_stats;
 
+  params.adaptive_sampling = RNA_boolean_get(&cscene, "use_adaptive_sampling");
+
   return params;
 }