Cycles: experimental correlated multi-jittered sampling pattern that can be used

instead of sobol. So far one doesn't seem to be consistently better or worse than
the other for the same number of samples but more testing is needed.

The random number generator itself is slower than sobol for most number of samples,
except 16, 64, 256, .. because they can be computed faster. This can probably be
optimized, but we can do that when/if this actually turns out to be useful.

Paper this implementation is based on:
http://graphics.pixar.com/library/MultiJitteredSampling/

Also includes some refactoring of RNG code, fixing a Sobol correlation issue with
the first BSDF and < 16 samples, skipping some unneeded RNG calls and using a
simpler unit square to unit disk function.

3 files changed, 25 insertions, 0 deletions

diff --git a/intern/cycles/render/integrator.cpp b/intern/cycles/render/integrator.cpp
index 731ffd9e271..cc369e7abc9 100644
--- a/intern/cycles/render/integrator.cpp
+++ b/intern/cycles/render/integrator.cpp
@@ -49,6 +49,7 @@ Integrator::Integrator()
 	sample_clamp = 0.0f;
 	motion_blur = false;
 
+	aa_samples = 0;
 	diffuse_samples = 1;
 	glossy_samples = 1;
 	transmission_samples = 1;
@@ -57,6 +58,8 @@ Integrator::Integrator()
 	subsurface_samples = 1;
 	progressive = true;
 
+	sampling_pattern = SAMPLING_PATTERN_SOBOL;
+
 	need_update = true;
 }
 
@@ -104,6 +107,7 @@ void Integrator::device_update(Device *device, DeviceScene *dscene, Scene *scene
 	kintegrator->sample_clamp = (sample_clamp == 0.0f)? FLT_MAX: sample_clamp*3.0f;
 
 	kintegrator->progressive = progressive;
+	kintegrator->aa_samples = aa_samples;
 	kintegrator->diffuse_samples = diffuse_samples;
 	kintegrator->glossy_samples = glossy_samples;
 	kintegrator->transmission_samples = transmission_samples;
@@ -111,6 +115,8 @@ void Integrator::device_update(Device *device, DeviceScene *dscene, Scene *scene
 	kintegrator->mesh_light_samples = mesh_light_samples;
 	kintegrator->subsurface_samples = subsurface_samples;
 
+	kintegrator->sampling_pattern = sampling_pattern;
+
 	/* sobol directions table */
 	int max_samples = 1;
 
@@ -160,6 +166,7 @@ bool Integrator::modified(const Integrator& integrator)
 		seed == integrator.seed &&
 		sample_clamp == integrator.sample_clamp &&
 		progressive == integrator.progressive &&
+		aa_samples == integrator.aa_samples &&
 		diffuse_samples == integrator.diffuse_samples &&
 		glossy_samples == integrator.glossy_samples &&
 		transmission_samples == integrator.transmission_samples &&
diff --git a/intern/cycles/render/integrator.h b/intern/cycles/render/integrator.h
index 9867e310d4d..fff24b506fb 100644
--- a/intern/cycles/render/integrator.h
+++ b/intern/cycles/render/integrator.h
@@ -19,6 +19,8 @@
 #ifndef __INTEGRATOR_H__
 #define __INTEGRATOR_H__
 
+#include "kernel_types.h"
+
 CCL_NAMESPACE_BEGIN
 
 class Device;
@@ -49,6 +51,7 @@ public:
 	float sample_clamp;
 	bool motion_blur;
 
+	int aa_samples;
 	int diffuse_samples;
 	int glossy_samples;
 	int transmission_samples;
@@ -58,6 +61,8 @@ public:
 
 	bool progressive;
 
+	SamplingPattern sampling_pattern;
+
 	bool need_update;
 
 	Integrator();
diff --git a/intern/cycles/render/session.cpp b/intern/cycles/render/session.cpp
index bc847d5719c..44364418dcf 100644
--- a/intern/cycles/render/session.cpp
+++ b/intern/cycles/render/session.cpp
@@ -22,6 +22,7 @@
 #include "buffers.h"
 #include "camera.h"
 #include "device.h"
+#include "integrator.h"
 #include "scene.h"
 #include "session.h"
 
@@ -728,6 +729,18 @@ void Session::update_scene()
 		cam->tag_update();
 	}
 
+	/* number of samples is needed by multi jittered sampling pattern */
+	Integrator *integrator = scene->integrator;
+
+	if(integrator->sampling_pattern == SAMPLING_PATTERN_CMJ) {
+		int aa_samples = tile_manager.num_samples;
+
+		if(aa_samples != integrator->aa_samples) {
+			integrator->aa_samples = aa_samples;
+			integrator->tag_update(scene);
+		}
+	}
+
 	/* update scene */
 	if(scene->need_update()) {
 		progress.set_status("Updating Scene");