There’s an Arnold error that recommends setting the load_at_init parameter, but people don’t always know where to find that in their favorite Arnold plugin.
ERROR| [proc] c4d|Arnold_Procedural: bounds supplied to procedural node are not large enough to contain the actual underlying geometry.
Replace given bounds: (-1, -1, -1) X (1, 1, 1), with: (-9.4028616, -9.43616867, -9.21633244) X (9.3304739, 9.43616867, 9.21633244).
Setting the procedural's load_at_init parameter to true would also fix this.
The load_at_init parameter controls whether the procedural (standin) is loaded during scene intialization (before rendering starts), or during rendering (when a ray hits the procedural bounding box).
By default, load_at_init is false, which means that procedural loading is deferred until render time.
And so, in MtoA, C4DtoA, and SItoA, the load_at_init parameter is exposed as Defer Standin Load, which is enabled by default. In HtoA, you have a Load At Init parameter on for the Arnold Procedural node.
In MtoA, Defer Standin Load is a parameter of the aiStandin node.
Merging your velocity vel.x, vel.y, and vel.z grids into a single vector grid using a Vdb Vector Merge node can speed up your renders.
You can safely ignore the “component grids have different transforms” warning on the VDB Vector Merge. The x, y, and z components of the velocity have slightly different transforms because they located on the center of the cell faces in each direction; that’s coming from the marker-and-cell (MAC) grid used in the simulation.
If you really want to be precise with the velocities, you need to resample them on the same grid, say the density grid:
A few quick notes about instancing support in HtoA:
For instancing, use the Instance object with fast point instancing. HtoA doesn’t support full point instancing.
You can assign material to instances with the shop_materialpath string attribute on the instance points.
Fast point instancing supports per-instance user data and instance OBJ property overrides.
Light instancing is not supported [yet]. Actually, Arnold itself doesn’t support light instances, but what plugins like MtoA and SItoA do is translate the light instances into duplicates of the light for Arnold.