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<p class="MsoNormal">I find this feature very useful! In application code, we commonly need to deal with variable-length arrays. We have been using std::vector accessors in C++ and adding vtkStringArray based or GetNumberOf…/GetNth… methods or for Python, which
has made the API complex and has been very inconvenient to use in Python.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">These arrays typically contain up to a few ten elements, therefore, for us, convenience is much more important than efficiency.<o:p></o:p></p>
<p class="MsoNormal"><o:p></o:p></p>
<p class="MsoNormal">Most often we return strings and vtkObject* in std::vector, so it would be great if vtkObject pointers would be supported, too.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Andras<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b>From:</b> vtk-developers <vtk-developers-bounces@public.kitware.com>
<b>On Behalf Of </b>Todd via vtk-developers<br>
<b>Sent:</b> Wednesday, September 5, 2018 8:16 PM<br>
<b>To:</b> David Gobbi <david.gobbi@gmail.com><br>
<b>Cc:</b> VTK Developers <vtk-developers@vtk.org><br>
<b>Subject:</b> Re: [vtk-developers] Added support for std::vector to the wrappers<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Hi David<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Since std::vector types are unlikely to be small, like coordinate and bound arrays, that sounds horribly inefficient; especially when large quantities of strings and objects are being marshalled.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Why not just map the std::vector/std::array to a Python iterator object?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Todd<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On 6 Sep 2018 4:20 a.m., David Gobbi <<a href="mailto:david.gobbi@gmail.com">david.gobbi@gmail.com</a>> wrote:<o:p></o:p></p>
<blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in">
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<p class="MsoNormal">Hi Folks,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Yesterday I merged a patch that allows std::vector<T> to be used from the Python wrappers, where T can be 'std::string' or any numeric type from 'signed char' to 'float' (including typedefs to those types).<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">This means that if you add a C++ method to VTK that takes std::vector<std::string>, then in Python you can pass a list or any other Python sequence and the wrappers will convert it to a vector for you.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Method examples that can accept any Python sequence:<o:p></o:p></p>
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<p class="MsoNormal"> void SetStrings(std::vector<std::string> strings);<o:p></o:p></p>
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<p class="MsoNormal"> void SetStrings(const std::vector<std::string>& strings);<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Method example that takes a Python mutable sequence (the C++ method can write back to the container, since this is pass-by-reference):<o:p></o:p></p>
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<p class="MsoNormal"> void GetStrings(std::vector<std::string>& strings);<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Method examples that return a vector (which is converted to a Python tuple):<o:p></o:p></p>
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<p class="MsoNormal"> const std::vector<std::string>& GetStrings();<o:p></o:p></p>
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<p class="MsoNormal"> std::vector<std::string>& GetStrings();<o:p></o:p></p>
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<p class="MsoNormal"> std::vector<std::string> GetStrings();<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Note that std::vector is not 'wrapped' per se. Instead, what is going on here is that the wrappers are converting to/from Python container types. My primary goal was convenience rather than efficiency, we can always add a wrapped std::vector
type at a later date without sacrificing the convenience of automatic conversion.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Chances are good that I'll be able to add std::vectors of VTK objects (smart or dumb pointers) and vtkVariant before VTK 9, but only if someone adds methods to VTK that take parameters of those types (as far as I know, there aren't any
yet).<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">See the following VTK gitlab issue for additional information:<o:p></o:p></p>
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<p class="MsoNormal"><a href="https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.kitware.com%2Fvtk%2Fvtk%2Fissues%2F17362&data=02%7C01%7Classo%40queensu.ca%7C0e1f3f218b5543a5524608d6138e03b5%7Cd61ecb3b38b142d582c4efb2838b925c%7C1%7C0%7C636717898021517951&sdata=9vohuaiduQLCm6pfGlMxQbXL4hYutf1fKB6SafvQE4c%3D&reserved=0">https://gitlab.kitware.com/vtk/vtk/issues/17362</a><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The following is a list of VTK methods that take std::vector that have been wrapped due to this change (it is a short list, since people have historically avoided using std::vector as part of the VTK public API due to the obvious reason
that they didn't want to exclude their methods from wrapping):<o:p></o:p></p>
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<p class="MsoNormal">vtkActor::ProcessSelectorPixelBuffers<o:p></o:p></p>
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<p class="MsoNormal">vtkAMRInformation::GetNumBlocks<o:p></o:p></p>
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<p class="MsoNormal">vtkCompositePolyDataMapper2::ProcessSelectorPixelBuffers<o:p></o:p></p>
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<p class="MsoNormal">vtkMapper::ProcessSelectorPixelBuffers<o:p></o:p></p>
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<p class="MsoNormal">vtkMultiProcessStream::GetRawData<o:p></o:p></p>
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<p class="MsoNormal">vtkMultiProcessStream::SetRawData<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLGlyph3DHelper::GlyphRender<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLIndexBufferObject::AppendTriangleIndexBuffer<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLIndexBufferObject::AppendLineIndexBuffer<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLIndexBufferObject::AppendTriangleLineIndexBuffer<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLIndexBufferObject::AppendPointIndexBuffer<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLIndexBufferObject::AppendStripIndexBuffer<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLIndexBufferObject::AppendEdgeFlagIndexBuffer<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLMoleculeMapper::ProcessSelectorPixelBuffers<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLPointGaussianMapper::ProcessSelectorPixelBuffers<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLPolyDataMapper::HandleAppleBug<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLPolyDataMapper::ProcessSelectorPixelBuffers<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLVertexBufferObject::SetShift<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLVertexBufferObject::SetScale<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLVertexBufferObject::GetShift<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLVertexBufferObject::GetScale<o:p></o:p></p>
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<p class="MsoNormal">vtkOpenGLVertexBufferObject::GetPackedVBO<o:p></o:p></p>
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<p class="MsoNormal">vtkParallelAMRUtilities::DistributeProcessInformation<o:p></o:p></p>
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<p class="MsoNormal">vtkProp::ProcessSelectorPixelBuffers<o:p></o:p></p>
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<p class="MsoNormal">vtkResourceFileLocator::Locate<o:p></o:p></p>
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<p class="MsoNormal">vtkShadowMapPass::ShadowMapTransforms<o:p></o:p></p>
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<p class="MsoNormal">vtkShadowMapPass::GetShadowMapTextureUnits<o:p></o:p></p>
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<p class="MsoNormal">vtkSparseArray::GetUniqueCoordinates<o:p></o:p></p>
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<p class="MsoNormal">vtkUnicodeString::utf16_str<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Cheers,<o:p></o:p></p>
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<p class="MsoNormal"> - David<o:p></o:p></p>
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</blockquote>
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<p class="MsoNormal"><o:p> </o:p></p>
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