Cycles: change volume step size controls, auto adjust based on voxel size

By default it will now set the step size to the voxel size for smoke and
volume objects, and 1/10th the bounding box for procedural volume shaders.

New settings are:
* Scene render/preview step rate: to globally adjust detail and performance
* Material step rate: multiplied with auto detected per-object step size
* World step size: distance to steo for world shader

Differential Revision: https://developer.blender.org/D1777

12 files changed, 106 insertions, 20 deletions

diff --git a/intern/cycles/render/background.cpp b/intern/cycles/render/background.cpp
index 6553ca735e4..5a61ead2c54 100644
--- a/intern/cycles/render/background.cpp
+++ b/intern/cycles/render/background.cpp
@@ -43,6 +43,8 @@ NODE_DEFINE(Background)
   SOCKET_BOOLEAN(transparent_glass, "Transparent Glass", false);
   SOCKET_FLOAT(transparent_roughness_threshold, "Transparent Roughness Threshold", 0.0f);
 
+  SOCKET_FLOAT(volume_step_size, "Volume Step Size", 0.1f);
+
   SOCKET_NODE(shader, "Shader", &Shader::node_type);
 
   return type;
@@ -91,6 +93,8 @@ void Background::device_update(Device *device, DeviceScene *dscene, Scene *scene
   else
     kbackground->volume_shader = SHADER_NONE;
 
+  kbackground->volume_step_size = volume_step_size * scene->integrator->volume_step_rate;
+
   /* No background node, make world shader invisible to all rays, to skip evaluation in kernel. */
   if (bg_shader->graph->nodes.size() <= 1) {
     kbackground->surface_shader |= SHADER_EXCLUDE_ANY;
diff --git a/intern/cycles/render/background.h b/intern/cycles/render/background.h
index fb27430f9a3..c2ca1f75179 100644
--- a/intern/cycles/render/background.h
+++ b/intern/cycles/render/background.h
@@ -45,6 +45,8 @@ class Background : public Node {
   bool transparent_glass;
   float transparent_roughness_threshold;
 
+  float volume_step_size;
+
   bool need_update;
 
   Background();
diff --git a/intern/cycles/render/integrator.cpp b/intern/cycles/render/integrator.cpp
index ee1aa5988bf..d856f7a300f 100644
--- a/intern/cycles/render/integrator.cpp
+++ b/intern/cycles/render/integrator.cpp
@@ -50,7 +50,7 @@ NODE_DEFINE(Integrator)
   SOCKET_INT(ao_bounces, "AO Bounces", 0);
 
   SOCKET_INT(volume_max_steps, "Volume Max Steps", 1024);
-  SOCKET_FLOAT(volume_step_size, "Volume Step Size", 0.1f);
+  SOCKET_FLOAT(volume_step_rate, "Volume Step Rate", 1.0f);
 
   SOCKET_BOOLEAN(caustics_reflective, "Reflective Caustics", true);
   SOCKET_BOOLEAN(caustics_refractive, "Refractive Caustics", true);
@@ -143,7 +143,7 @@ void Integrator::device_update(Device *device, DeviceScene *dscene, Scene *scene
   }
 
   kintegrator->volume_max_steps = volume_max_steps;
-  kintegrator->volume_step_size = volume_step_size;
+  kintegrator->volume_step_rate = volume_step_rate;
 
   kintegrator->caustics_reflective = caustics_reflective;
   kintegrator->caustics_refractive = caustics_refractive;
diff --git a/intern/cycles/render/integrator.h b/intern/cycles/render/integrator.h
index 9930e907aea..9804caebe6e 100644
--- a/intern/cycles/render/integrator.h
+++ b/intern/cycles/render/integrator.h
@@ -45,7 +45,7 @@ class Integrator : public Node {
   int ao_bounces;
 
   int volume_max_steps;
-  float volume_step_size;
+  float volume_step_rate;
 
   bool caustics_reflective;
   bool caustics_refractive;
diff --git a/intern/cycles/render/object.cpp b/intern/cycles/render/object.cpp
index 4987b6089d7..c84007823d2 100644
--- a/intern/cycles/render/object.cpp
+++ b/intern/cycles/render/object.cpp
@@ -17,6 +17,7 @@
 #include "render/camera.h"
 #include "device/device.h"
 #include "render/hair.h"
+#include "render/integrator.h"
 #include "render/light.h"
 #include "render/mesh.h"
 #include "render/curves.h"
@@ -65,6 +66,7 @@ struct UpdateObjectTransformState {
   KernelObject *objects;
   Transform *object_motion_pass;
   DecomposedTransform *object_motion;
+  float *object_volume_step;
 
   /* Flags which will be synchronized to Integrator. */
   bool have_motion;
@@ -266,6 +268,65 @@ uint Object::visibility_for_tracing() const
   return trace_visibility;
 }
 
+float Object::compute_volume_step_size() const
+{
+  if (!geometry->has_volume) {
+    return FLT_MAX;
+  }
+
+  /* Compute step rate from shaders. */
+  float step_rate = FLT_MAX;
+
+  foreach (Shader *shader, geometry->used_shaders) {
+    if (shader->has_volume) {
+      if ((shader->heterogeneous_volume && shader->has_volume_spatial_varying) ||
+          (shader->has_volume_attribute_dependency)) {
+        step_rate = fminf(shader->volume_step_rate, step_rate);
+      }
+    }
+  }
+
+  if (step_rate == FLT_MAX) {
+    return FLT_MAX;
+  }
+
+  /* Compute step size from voxel grids. */
+  float step_size = FLT_MAX;
+
+  foreach (Attribute &attr, geometry->attributes.attributes) {
+    if (attr.element == ATTR_ELEMENT_VOXEL) {
+      ImageHandle &handle = attr.data_voxel();
+      const ImageMetaData &metadata = handle.metadata();
+      if (metadata.width == 0 || metadata.height == 0 || metadata.depth == 0) {
+        continue;
+      }
+
+      /* Step size is transformed from voxel to world space. */
+      Transform voxel_tfm = tfm;
+      if (metadata.use_transform_3d) {
+        voxel_tfm = tfm * transform_inverse(metadata.transform_3d);
+      }
+
+      float3 size = make_float3(
+          1.0f / metadata.width, 1.0f / metadata.height, 1.0f / metadata.depth);
+      float voxel_step_size = min3(fabs(transform_direction(&voxel_tfm, size)));
+
+      if (voxel_step_size > 0.0f) {
+        step_size = fminf(voxel_step_size, step_size);
+      }
+    }
+  }
+
+  if (step_size == FLT_MAX) {
+    /* Fall back to 1/10th of bounds for procedural volumes. */
+    step_size = 0.1f * average(bounds.size());
+  }
+
+  step_size *= step_rate;
+
+  return step_size;
+}
+
 int Object::get_device_index() const
 {
   return index;
@@ -451,6 +512,7 @@ void ObjectManager::device_update_object_transform(UpdateObjectTransformState *s
     flag |= SD_OBJECT_HOLDOUT_MASK;
   }
   state->object_flag[ob->index] = flag;
+  state->object_volume_step[ob->index] = FLT_MAX;
 
   /* Have curves. */
   if (geom->type == Geometry::HAIR) {
@@ -504,6 +566,7 @@ void ObjectManager::device_update_transforms(DeviceScene *dscene, Scene *scene,
 
   state.objects = dscene->objects.alloc(scene->objects.size());
   state.object_flag = dscene->object_flag.alloc(scene->objects.size());
+  state.object_volume_step = dscene->object_volume_step.alloc(scene->objects.size());
   state.object_motion = NULL;
   state.object_motion_pass = NULL;
 
@@ -624,6 +687,7 @@ void ObjectManager::device_update_flags(
 
   /* Object info flag. */
   uint *object_flag = dscene->object_flag.data();
+  float *object_volume_step = dscene->object_volume_step.data();
 
   /* Object volume intersection. */
   vector<Object *> volume_objects;
@@ -634,6 +698,10 @@ void ObjectManager::device_update_flags(
         volume_objects.push_back(object);
       }
       has_volume_objects = true;
+      object_volume_step[object->index] = object->compute_volume_step_size();
+    }
+    else {
+      object_volume_step[object->index] = FLT_MAX;
     }
   }
 
@@ -651,6 +719,7 @@ void ObjectManager::device_update_flags(
     else {
       object_flag[object->index] &= ~(SD_OBJECT_HAS_VOLUME | SD_OBJECT_HAS_VOLUME_ATTRIBUTES);
     }
+
     if (object->is_shadow_catcher) {
       object_flag[object->index] |= SD_OBJECT_SHADOW_CATCHER;
     }
@@ -679,6 +748,7 @@ void ObjectManager::device_update_flags(
 
   /* Copy object flag. */
   dscene->object_flag.copy_to_device();
+  dscene->object_volume_step.copy_to_device();
 }
 
 void ObjectManager::device_update_mesh_offsets(Device *, DeviceScene *dscene, Scene *scene)
@@ -725,6 +795,7 @@ void ObjectManager::device_free(Device *, DeviceScene *dscene)
   dscene->object_motion_pass.free();
   dscene->object_motion.free();
   dscene->object_flag.free();
+  dscene->object_volume_step.free();
 }
 
 void ObjectManager::apply_static_transforms(DeviceScene *dscene, Scene *scene, Progress &progress)
diff --git a/intern/cycles/render/object.h b/intern/cycles/render/object.h
index 7bd3edf769b..2c2870cd0f2 100644
--- a/intern/cycles/render/object.h
+++ b/intern/cycles/render/object.h
@@ -97,6 +97,9 @@ class Object : public Node {
   /* Returns the index that is used in the kernel for this object. */
   int get_device_index() const;
 
+  /* Compute step size from attributes, shaders, transforms. */
+  float compute_volume_step_size() const;
+
  protected:
   /* Specifies the position of the object in scene->objects and
    * in the device vectors. Gets set in device_update. */
diff --git a/intern/cycles/render/osl.cpp b/intern/cycles/render/osl.cpp
index d17d7270cd5..74eb61e2dff 100644
--- a/intern/cycles/render/osl.cpp
+++ b/intern/cycles/render/osl.cpp
@@ -760,16 +760,14 @@ void OSLCompiler::add(ShaderNode *node, const char *name, bool isfilepath)
   else if (current_type == SHADER_TYPE_VOLUME) {
     if (node->has_spatial_varying())
       current_shader->has_volume_spatial_varying = true;
+    if (node->has_attribute_dependency())
+      current_shader->has_volume_attribute_dependency = true;
   }
 
   if (node->has_object_dependency()) {
     current_shader->has_object_dependency = true;
   }
 
-  if (node->has_attribute_dependency()) {
-    current_shader->has_attribute_dependency = true;
-  }
-
   if (node->has_integrator_dependency()) {
     current_shader->has_integrator_dependency = true;
   }
@@ -1143,8 +1141,8 @@ void OSLCompiler::compile(OSLGlobals *og, Shader *shader)
     shader->has_displacement = false;
     shader->has_surface_spatial_varying = false;
     shader->has_volume_spatial_varying = false;
+    shader->has_volume_attribute_dependency = false;
     shader->has_object_dependency = false;
-    shader->has_attribute_dependency = false;
     shader->has_integrator_dependency = false;
 
     /* generate surface shader */
diff --git a/intern/cycles/render/scene.cpp b/intern/cycles/render/scene.cpp
index 76f62fd6690..77c66779c20 100644
--- a/intern/cycles/render/scene.cpp
+++ b/intern/cycles/render/scene.cpp
@@ -63,6 +63,7 @@ DeviceScene::DeviceScene(Device *device)
       object_motion_pass(device, "__object_motion_pass", MEM_GLOBAL),
       object_motion(device, "__object_motion", MEM_GLOBAL),
       object_flag(device, "__object_flag", MEM_GLOBAL),
+      object_volume_step(device, "__object_volume_step", MEM_GLOBAL),
       camera_motion(device, "__camera_motion", MEM_GLOBAL),
       attributes_map(device, "__attributes_map", MEM_GLOBAL),
       attributes_float(device, "__attributes_float", MEM_GLOBAL),
diff --git a/intern/cycles/render/scene.h b/intern/cycles/render/scene.h
index d2570138b53..6b10a901d7b 100644
--- a/intern/cycles/render/scene.h
+++ b/intern/cycles/render/scene.h
@@ -91,6 +91,7 @@ class DeviceScene {
   device_vector<Transform> object_motion_pass;
   device_vector<DecomposedTransform> object_motion;
   device_vector<uint> object_flag;
+  device_vector<float> object_volume_step;
 
   /* cameras */
   device_vector<DecomposedTransform> camera_motion;
diff --git a/intern/cycles/render/shader.cpp b/intern/cycles/render/shader.cpp
index cc6eb2e5e7f..747fc58f81a 100644
--- a/intern/cycles/render/shader.cpp
+++ b/intern/cycles/render/shader.cpp
@@ -178,6 +178,8 @@ NODE_DEFINE(Shader)
               volume_interpolation_method_enum,
               VOLUME_INTERPOLATION_LINEAR);
 
+  SOCKET_FLOAT(volume_step_rate, "Volume Step Rate", 1.0f);
+
   static NodeEnum displacement_method_enum;
   displacement_method_enum.insert("bump", DISPLACE_BUMP);
   displacement_method_enum.insert("true", DISPLACE_TRUE);
@@ -203,10 +205,11 @@ Shader::Shader() : Node(node_type)
   has_bssrdf_bump = false;
   has_surface_spatial_varying = false;
   has_volume_spatial_varying = false;
+  has_volume_attribute_dependency = false;
   has_object_dependency = false;
-  has_attribute_dependency = false;
   has_integrator_dependency = false;
   has_volume_connected = false;
+  prev_volume_step_rate = 0.0f;
 
   displacement_method = DISPLACE_BUMP;
 
@@ -353,9 +356,10 @@ void Shader::tag_update(Scene *scene)
     scene->geometry_manager->need_update = true;
   }
 
-  if (has_volume != prev_has_volume) {
+  if (has_volume != prev_has_volume || volume_step_rate != prev_volume_step_rate) {
     scene->geometry_manager->need_flags_update = true;
     scene->object_manager->need_flags_update = true;
+    prev_volume_step_rate = volume_step_rate;
   }
 }
 
@@ -533,10 +537,12 @@ void ShaderManager::device_update_common(Device *device,
     /* in this case we can assume transparent surface */
     if (shader->has_volume_connected && !shader->has_surface)
       flag |= SD_HAS_ONLY_VOLUME;
-    if (shader->heterogeneous_volume && shader->has_volume_spatial_varying)
-      flag |= SD_HETEROGENEOUS_VOLUME;
-    if (shader->has_attribute_dependency)
-      flag |= SD_NEED_ATTRIBUTES;
+    if (shader->has_volume) {
+      if (shader->heterogeneous_volume && shader->has_volume_spatial_varying)
+        flag |= SD_HETEROGENEOUS_VOLUME;
+    }
+    if (shader->has_volume_attribute_dependency)
+      flag |= SD_NEED_VOLUME_ATTRIBUTES;
     if (shader->has_bssrdf_bump)
       flag |= SD_HAS_BSSRDF_BUMP;
     if (device->info.has_volume_decoupled) {
diff --git a/intern/cycles/render/shader.h b/intern/cycles/render/shader.h
index 5a5b42de994..1509150228f 100644
--- a/intern/cycles/render/shader.h
+++ b/intern/cycles/render/shader.h
@@ -92,6 +92,8 @@ class Shader : public Node {
   bool heterogeneous_volume;
   VolumeSampling volume_sampling_method;
   int volume_interpolation_method;
+  float volume_step_rate;
+  float prev_volume_step_rate;
 
   /* synchronization */
   bool need_update;
@@ -118,8 +120,8 @@ class Shader : public Node {
   bool has_bssrdf_bump;
   bool has_surface_spatial_varying;
   bool has_volume_spatial_varying;
+  bool has_volume_attribute_dependency;
   bool has_object_dependency;
-  bool has_attribute_dependency;
   bool has_integrator_dependency;
 
   /* displacement */
diff --git a/intern/cycles/render/svm.cpp b/intern/cycles/render/svm.cpp
index 2946614a3b7..c4218f7df1e 100644
--- a/intern/cycles/render/svm.cpp
+++ b/intern/cycles/render/svm.cpp
@@ -444,16 +444,14 @@ void SVMCompiler::generate_node(ShaderNode *node, ShaderNodeSet &done)
   else if (current_type == SHADER_TYPE_VOLUME) {
     if (node->has_spatial_varying())
       current_shader->has_volume_spatial_varying = true;
+    if (node->has_attribute_dependency())
+      current_shader->has_volume_attribute_dependency = true;
   }
 
   if (node->has_object_dependency()) {
     current_shader->has_object_dependency = true;
   }
 
-  if (node->has_attribute_dependency()) {
-    current_shader->has_attribute_dependency = true;
-  }
-
   if (node->has_integrator_dependency()) {
     current_shader->has_integrator_dependency = true;
   }
@@ -864,8 +862,8 @@ void SVMCompiler::compile(Shader *shader, array<int4> &svm_nodes, int index, Sum
   shader->has_displacement = false;
   shader->has_surface_spatial_varying = false;
   shader->has_volume_spatial_varying = false;
+  shader->has_volume_attribute_dependency = false;
   shader->has_object_dependency = false;
-  shader->has_attribute_dependency = false;
   shader->has_integrator_dependency = false;
 
   /* generate bump shader */