1 files changed, 65 insertions, 44 deletions

diff --git a/intern/cycles/kernel/closure/volume.h b/intern/cycles/kernel/closure/volume.h
index 1430f712701..69959a3f21b 100644
--- a/intern/cycles/kernel/closure/volume.h
+++ b/intern/cycles/kernel/closure/volume.h
@@ -14,8 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef __VOLUME_H__
-#define __VOLUME_H__
+#pragma once
 
 CCL_NAMESPACE_BEGIN
 
@@ -62,21 +61,12 @@ ccl_device int volume_henyey_greenstein_setup(HenyeyGreensteinVolume *volume)
   return SD_SCATTER;
 }
 
-ccl_device bool volume_henyey_greenstein_merge(const ShaderClosure *a, const ShaderClosure *b)
-{
-  const HenyeyGreensteinVolume *volume_a = (const HenyeyGreensteinVolume *)a;
-  const HenyeyGreensteinVolume *volume_b = (const HenyeyGreensteinVolume *)b;
-
-  return (volume_a->g == volume_b->g);
-}
-
-ccl_device float3 volume_henyey_greenstein_eval_phase(const ShaderClosure *sc,
+ccl_device float3 volume_henyey_greenstein_eval_phase(const ShaderVolumeClosure *svc,
                                                       const float3 I,
                                                       float3 omega_in,
                                                       float *pdf)
 {
-  const HenyeyGreensteinVolume *volume = (const HenyeyGreensteinVolume *)sc;
-  float g = volume->g;
+  float g = svc->g;
 
   /* note that I points towards the viewer */
   if (fabsf(g) < 1e-3f) {
@@ -122,7 +112,7 @@ henyey_greenstrein_sample(float3 D, float g, float randu, float randv, float *pd
   return dir;
 }
 
-ccl_device int volume_henyey_greenstein_sample(const ShaderClosure *sc,
+ccl_device int volume_henyey_greenstein_sample(const ShaderVolumeClosure *svc,
                                                float3 I,
                                                float3 dIdx,
                                                float3 dIdy,
@@ -134,8 +124,7 @@ ccl_device int volume_henyey_greenstein_sample(const ShaderClosure *sc,
                                                float3 *domega_in_dy,
                                                float *pdf)
 {
-  const HenyeyGreensteinVolume *volume = (const HenyeyGreensteinVolume *)sc;
-  float g = volume->g;
+  float g = svc->g;
 
   /* note that I points towards the viewer and so is used negated */
   *omega_in = henyey_greenstrein_sample(-I, g, randu, randv, pdf);
@@ -153,17 +142,15 @@ ccl_device int volume_henyey_greenstein_sample(const ShaderClosure *sc,
 /* VOLUME CLOSURE */
 
 ccl_device float3 volume_phase_eval(const ShaderData *sd,
-                                    const ShaderClosure *sc,
+                                    const ShaderVolumeClosure *svc,
                                     float3 omega_in,
                                     float *pdf)
 {
-  kernel_assert(sc->type == CLOSURE_VOLUME_HENYEY_GREENSTEIN_ID);
-
-  return volume_henyey_greenstein_eval_phase(sc, sd->I, omega_in, pdf);
+  return volume_henyey_greenstein_eval_phase(svc, sd->I, omega_in, pdf);
 }
 
 ccl_device int volume_phase_sample(const ShaderData *sd,
-                                   const ShaderClosure *sc,
+                                   const ShaderVolumeClosure *svc,
                                    float randu,
                                    float randv,
                                    float3 *eval,
@@ -171,31 +158,65 @@ ccl_device int volume_phase_sample(const ShaderData *sd,
                                    differential3 *domega_in,
                                    float *pdf)
 {
-  int label;
-
-  switch (sc->type) {
-    case CLOSURE_VOLUME_HENYEY_GREENSTEIN_ID:
-      label = volume_henyey_greenstein_sample(sc,
-                                              sd->I,
-                                              sd->dI.dx,
-                                              sd->dI.dy,
-                                              randu,
-                                              randv,
-                                              eval,
-                                              omega_in,
-                                              &domega_in->dx,
-                                              &domega_in->dy,
-                                              pdf);
-      break;
-    default:
-      *eval = make_float3(0.0f, 0.0f, 0.0f);
-      label = LABEL_NONE;
-      break;
+  return volume_henyey_greenstein_sample(svc,
+                                         sd->I,
+                                         sd->dI.dx,
+                                         sd->dI.dy,
+                                         randu,
+                                         randv,
+                                         eval,
+                                         omega_in,
+                                         &domega_in->dx,
+                                         &domega_in->dy,
+                                         pdf);
+}
+
+/* Volume sampling utilities. */
+
+/* todo: this value could be tweaked or turned into a probability to avoid
+ * unnecessary work in volumes and subsurface scattering. */
+#define VOLUME_THROUGHPUT_EPSILON 1e-6f
+
+ccl_device float3 volume_color_transmittance(float3 sigma, float t)
+{
+  return exp3(-sigma * t);
+}
+
+ccl_device float volume_channel_get(float3 value, int channel)
+{
+  return (channel == 0) ? value.x : ((channel == 1) ? value.y : value.z);
+}
+
+ccl_device int volume_sample_channel(float3 albedo, float3 throughput, float rand, float3 *pdf)
+{
+  /* Sample color channel proportional to throughput and single scattering
+   * albedo, to significantly reduce noise with many bounce, following:
+   *
+   * "Practical and Controllable Subsurface Scattering for Production Path
+   *  Tracing". Matt Jen-Yuan Chiang, Peter Kutz, Brent Burley. SIGGRAPH 2016. */
+  float3 weights = fabs(throughput * albedo);
+  float sum_weights = weights.x + weights.y + weights.z;
+  float3 weights_pdf;
+
+  if (sum_weights > 0.0f) {
+    weights_pdf = weights / sum_weights;
   }
+  else {
+    weights_pdf = make_float3(1.0f / 3.0f, 1.0f / 3.0f, 1.0f / 3.0f);
+  }
+
+  *pdf = weights_pdf;
 
-  return label;
+  /* OpenCL does not support -> on float3, so don't use pdf->x. */
+  if (rand < weights_pdf.x) {
+    return 0;
+  }
+  else if (rand < weights_pdf.x + weights_pdf.y) {
+    return 1;
+  }
+  else {
+    return 2;
+  }
 }
 
 CCL_NAMESPACE_END
-
-#endif