Build grid for NanoVDB volumes

scene/volume/spatial_field/NanoVDBField.cpp

@@ -48,6 +48,10 @@ void NanoVDBField::commit()
 
   vfield.voxelSpaceTransform = mat4x3(mat3::identity(),float3{0.f,0.f,0.f});
 
+  buildGrid();
+
+  vfield.gridAccel = m_gridAccel.visionarayAccel();
+
   dispatch();
 }
 
@@ -68,4 +72,39 @@ aabb NanoVDBField::bounds() const
               {(float)upper[0], (float)upper[1], (float)upper[2]}};
 }
 
+void NanoVDBField::buildGrid()
+{
+#if defined(WITH_CUDA) || defined(WITH_HIP)
+  return;
+#endif
+  int3 gridDims{64, 64, 64};
+  box3f worldBounds = {bounds().min,bounds().max};
+  m_gridAccel.init(gridDims, worldBounds);
+
+  dco::GridAccel &vaccel = m_gridAccel.visionarayAccel();
+  auto acc = vfield.asNanoVDB.grid->getAccessor();
+
+  float3 mcSize = (worldBounds.max-worldBounds.min) / float3(gridDims);
+
+  for (unsigned mcz=0; mcz<gridDims.z; ++mcz) {
+    for (unsigned mcy=0; mcy<gridDims.y; ++mcy) {
+      for (unsigned mcx=0; mcx<gridDims.x; ++mcx) {
+        const vec3i mcID(mcx,mcy,mcz);
+        box3f mcBounds{worldBounds.min+mcSize*float3(mcx,mcy,mcz),
+                       worldBounds.min+mcSize*float3(mcx+1,mcy+1,mcz+1)};
+
+        nanovdb::CoordBBox bbox(
+            {(int)mcBounds.min.x,(int)mcBounds.min.y,(int)mcBounds.min.z},
+            {(int)mcBounds.max.x+1,(int)mcBounds.max.y+1,(int)mcBounds.max.z+1});
+
+        for (nanovdb::CoordBBox::Iterator iter = bbox.begin(); iter; ++iter) {
+          float value = acc.getValue(*iter);
+          updateMC(mcID,gridDims,value,vaccel.valueRanges);
+          updateMCStepSize(mcID,gridDims,0.5f,vaccel.stepSizes); // TODO!?
+        }
+      }
+    }
+  }
+}
+
 } // namespace visionaray

scene/volume/spatial_field/NanoVDBField.h

@@ -23,6 +23,8 @@ struct NanoVDBField : public SpatialField
   bool isValid() const override;
 
   aabb bounds() const override;
+
+  void buildGrid() override;
  private:
 
   helium::IntrusivePtr<Array1D> m_gridData;