[vtkusers] VTK 7.1 vtkDataArray changes, current best way to copy vtkPolyData data?

[Allie Vacanti]

I think the best way to handle this would be to use a temporary
vtkDataArray that uses your buffer in-situ and then DeepCopy() it into
the target array. vtkDataArray::DeepCopy is optimized to copy AoS->AoS
and SoA->SoA efficiently, while falling back to a slower path for
other copy types. For example:

double *aosArrayData = ...;
vtkNew<vtkDoubleArray> output;
{ // Limit tmp's scope
  vtkNew<vtkDoubleArray> tmp;
  tmp->SetArray(aosArrayData, ...);
  output->DeepCopy(tmp);
}

is an AoS --> AoS  same-type copy, and is implemented as a simple
std::copy call (which the STL will resolve to a memcpy).

HTH,
Allie

On Thu, Sep 14, 2017 at 10:38 AM, Andy Bauer <andy.bauer at kitware.com> wrote:
> Hi Sean,
>
> You'd have to do the copy yourself in this case. Also, in this case I think
> it's valid to use the GetVoidPointer() after you've set the number of tuples
> and components and do a memcpy yourself as you know that it will be in the
> "legacy" VTK ordering style because you're manually creating it. With the
> alternate memory layouts of vtkDataArray derived classes it's very bad
> practice to use the GetVoidPointer() method for arrays of unknown origin
> since if it is in the SOA layout it will have to do a deep copy to get it
> into the AOS layout.
>
> Cheers,
> Andy
>
> On Thu, Sep 14, 2017 at 10:34 AM, Sean McBride <sean at rogue-research.com>
> wrote:
>>
>> Following-up on an older thread...
>>
>> First, thanks!
>>
>> Now I'm interested in the opposite.  That is, I have an existing raw
>> buffer of say doubles that comes from somewhere else.  I want to create a
>> vtkDoubleArray that *copies* the data.  Is there any API that takes a raw
>> buffer and does a memcpy?  Otherwise is it best to call InsertNextTuple() in
>> a loop?
>>
>> Cheers,
>>
>> Sean
>>
>>
>> On Fri, 9 Jun 2017 09:42:12 -0400, David Lonie said:
>>
>> >If you just want to dump the data from any vtkDataArray into a memory
>> >buffer using AOS ordering (e.g. typical VTK memory layout with
>> >coherent tuples), something like:
>> >
>> >vtkDataArray *array = ...;
>> >int bufSize = array->GetNumberOfValues() * array->GetDataTypeSize();
>> >void *buffer = malloc(bufSize);
>> >array->ExportToVoidPointer(buffer);
>> >
>> >will be the most efficient way to do this.
>> >
>> >HTH,
>> >Dave
>> >
>> >On Thu, Jun 8, 2017 at 12:14 PM, Sean McBride <sean at rogue-research.com>
>> > wrote:
>> >> Hi all,
>> >>
>> >> Since the vtkDataArray changes in VTK 7.1, what is the current best/
>> >fastest way to extract the points, strips, and normals from a
>> >vtkPolyData into another memory buffer?
>> >>
>> >> I'm always working with the same kind of data, so I'm hoping to
>> >preflight the sizes/types and then basically memcpy() the data out.
>>
>>
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