Accessing strided array without copying

[odarbs]

I have setup a simple uniform mesh of a cube and am trying to associate a strided array with a field using set_external, the data layout is an array of structures of 5 floats and I believe I can pass that information to the conduit node by giving it the offset, stride and size of the element all in bytes:

mesh["fields/V/values"].set_external(cellData.device, numCells, 1 * sizeof(float), 5 * sizeof(float), sizeof(float));

when I pass the host side pointer I get the following error:

Execution failed with vtkm: Could not find appropriate cast for array in CastAndCall.
Array: valueType=float storageType=vtkm::cont::StorageTagStride 16777216 values occupying 67108864 bytes [1 1 1 ... 1 1 1]
TypeList: vtkm::List<float, double>

when I pass the device side pointer I get a seg fault.

If I don't pass any of the offset and stride information everything works and I can generate a plot of the field, it's just stripy! Is this type of AoS data layout supported or do I need to take a different approach?

[cyrush]

We should be able to support this -- but we may need to check the paths where we wrap strided data.

Q: Is this on an NVIDIA system?

[odarbs]

Great. Yes this is on an NVIDIA system, I'm using version 12.6 of the CUDA toolkit to build.

[jfavre]

I am seeing this issue not only with CUDA-enabled Ascent, but also with a non-CUDA compilation.
I have build a reproducer which integrates into the testing infrastructure. File t_ascent_AOS_rendering.cpp creates a simple point cloud of 8 vertices with an AOS structure. Extracting it to a BluePrint file works fine (as verified with VisIt), but rendering fails with the same error "Could not find appropriate cast for array in CastAndCall"

Further, I have verified that vtkm (2.2 and 2.3) properly renders AOS data with another "vtk-m only" test.

Hope this test can help developers debug it.

t_ascent_AOS_rendering.cpp.gz

[nicolemarsaglia]

Thank you @jfavre for the artifacts. I've duplicated the CastAndCall error.

But, oddly, my blueprint extract in visit is coming up blank. I will keep investigating.

[cyrush]

Related viskores issue: Viskores/viskores#106