Cycles: Make Embree compact BVH optional

Make the Embree RTC_SCENE_FLAG_COMPACT flag optional and enabled per default.
Disabling it makes CPU rendering a bit faster in some scenes at the cost of a higher memory usage.

Barbershop renders about 3% faster, victor about 4% on CPU with compact BVH disabled.

Differential Revision: https://developer.blender.org/D13592

intern/cycles/blender/addon/properties.py

@@ -667,6 +667,11 @@ class CyclesRenderSettings(bpy.types.PropertyGroup):
         description="Use special type BVH optimized for hair (uses more ram but renders faster)",
         default=True,
     )
+    debug_use_compact_bvh: BoolProperty(
+        name="Use Compact BVH",
+        description="Use compact BVH structure (uses less ram but renders slower)",
+        default=True,
+    )
     debug_bvh_time_steps: IntProperty(
         name="BVH Time Steps",
         description="Split BVH primitives by this number of time steps to speed up render time in cost of memory",

intern/cycles/blender/addon/ui.py

@@ -689,6 +689,8 @@ class CYCLES_RENDER_PT_performance_acceleration_structure(CyclesButtonsPanel, Pa
         sub.active = not cscene.debug_use_spatial_splits and not use_embree
         sub.prop(cscene, "debug_bvh_time_steps")
 
+        col.prop(cscene, "debug_use_compact_bvh")
+
 
 class CYCLES_RENDER_PT_performance_final_render(CyclesButtonsPanel, Panel):
     bl_label = "Final Render"

intern/cycles/blender/sync.cpp

@@ -787,6 +787,7 @@ SceneParams BlenderSync::get_scene_params(BL::Scene &b_scene, bool background)
     params.bvh_type = BVH_TYPE_DYNAMIC;
 
   params.use_bvh_spatial_split = RNA_boolean_get(&cscene, "debug_use_spatial_splits");
+  params.use_bvh_compact_structure = RNA_boolean_get(&cscene, "debug_use_compact_bvh");
   params.use_bvh_unaligned_nodes = RNA_boolean_get(&cscene, "debug_use_hair_bvh");
   params.num_bvh_time_steps = RNA_int_get(&cscene, "debug_bvh_time_steps");
 

intern/cycles/bvh/embree.cpp

@@ -355,10 +355,12 @@ void BVHEmbree::build(Progress &progress, Stats *stats, RTCDevice rtc_device_)
   }
 
   const bool dynamic = params.bvh_type == BVH_TYPE_DYNAMIC;
+  const bool compact = params.use_compact_structure;
 
   scene = rtcNewScene(rtc_device);
   const RTCSceneFlags scene_flags = (dynamic ? RTC_SCENE_FLAG_DYNAMIC : RTC_SCENE_FLAG_NONE) |
-                                    RTC_SCENE_FLAG_COMPACT | RTC_SCENE_FLAG_ROBUST;
+                                    (compact ? RTC_SCENE_FLAG_COMPACT : RTC_SCENE_FLAG_NONE) |
+                                    RTC_SCENE_FLAG_ROBUST;
   rtcSetSceneFlags(scene, scene_flags);
   build_quality = dynamic ? RTC_BUILD_QUALITY_LOW :
                             (params.use_spatial_split ? RTC_BUILD_QUALITY_HIGH :

intern/cycles/bvh/params.h

@@ -97,6 +97,9 @@ class BVHParams {
    */
   bool use_unaligned_nodes;
 
+  /* Use compact acceleration structure (Embree)*/
+  bool use_compact_structure;
+
   /* Split time range to this number of steps and create leaf node for each
    * of this time steps.
    *

intern/cycles/scene/geometry.cpp

@@ -236,6 +236,7 @@ void Geometry::compute_bvh(
 
       BVHParams bparams;
       bparams.use_spatial_split = params->use_bvh_spatial_split;
+      bparams.use_compact_structure = params->use_bvh_compact_structure;
       bparams.bvh_layout = bvh_layout;
       bparams.use_unaligned_nodes = dscene->data.bvh.have_curves &&
                                     params->use_bvh_unaligned_nodes;

intern/cycles/scene/scene.h

@@ -160,6 +160,7 @@ class SceneParams {
 
   BVHType bvh_type;
   bool use_bvh_spatial_split;
+  bool use_bvh_compact_structure;
   bool use_bvh_unaligned_nodes;
   int num_bvh_time_steps;
   int hair_subdivisions;
@@ -174,6 +175,7 @@ class SceneParams {
     bvh_layout = BVH_LAYOUT_BVH2;
     bvh_type = BVH_TYPE_DYNAMIC;
     use_bvh_spatial_split = false;
+    use_bvh_compact_structure = true;
     use_bvh_unaligned_nodes = true;
     num_bvh_time_steps = 0;
     hair_subdivisions = 3;
@@ -187,6 +189,7 @@ class SceneParams {
     return !(shadingsystem == params.shadingsystem && bvh_layout == params.bvh_layout &&
              bvh_type == params.bvh_type &&
              use_bvh_spatial_split == params.use_bvh_spatial_split &&
+             use_bvh_compact_structure == params.use_bvh_compact_structure &&
              use_bvh_unaligned_nodes == params.use_bvh_unaligned_nodes &&
              num_bvh_time_steps == params.num_bvh_time_steps &&
              hair_subdivisions == params.hair_subdivisions && hair_shape == params.hair_shape &&