[vtkusers] Flat interpolation under OpenGL2 backend

Mon Feb 22 09:51:16 EST 2016

Hello,

If the data is in there, a combination of :
SetScalarModeToUseCellData()
GetCellData()->SetActiveScalars( "TEMP" );
should probably do the trick

The SetActiveScalars( "TEMP" ) should be called on the output of the
geometryFIlter which -I think- is not the case in the code that was posted:

Maybe something like this :

*************************************
geometryFilter->Update();
vtkPolyData* polydata = geometryFilter->GetOutput();
polydata->GetCellData()->SetActiveScalars( "TEMP" );
colorMapper->SetInputData( polydata );
colorMapper->ScalarVisibilityOn();
colorMapper->SetScalarModeToUseCellData();
colorMapper->SetScalarRange(297, 637);
**************************************
?

Simon

2016-02-22 15:21 GMT+01:00 Fernando Nellmeldin <
f.nellmeldin at open-engineering.com>:

> Hi, thank you for your response Simon.
> I tried your suggestions. Adding SetScalarModeToUseCellData didn't solve
> the problem :( (still I'm seeing all the model in white)
> I saved my results to load them in ParaView and indeed I can see a new
> Cell Data named "TEMP" with the values of the Point Data as I wish.
> Thus, I think that the point2celldata is working properly, and I have only
> a problem of configuring something to see it, but where?
>
> Any thoughs?
>
> Thank you.
>
> 2016-02-22 14:28 GMT+01:00 Simon ESNEAULT <simon.esneault at gmail.com>:
>
>> Hello,
>>
>> Not sure, but maybe a call to
>> SetScalarModeToUseCellData()
>> is needed on the mapper ?
>> You should try to save/load the dataset in paraview after it is processed
>> to see what's going on with the cell/point data :)
>>
>> Good luck
>> Simon
>>
>>
>>
>> 2016-02-22 13:23 GMT+01:00 Fernando Nellmeldin <
>> f.nellmeldin at open-engineering.com>:
>>
>>> Hello again.
>>> Yes, you understood the issue perfectly. And I understand the reason as
>>> of why is not working anymore, thank you for the great explanation.
>>>
>>> After your advise, I tried using vtkPointDataToCellData, but without
>>> success.
>>> Here is one small example I wrote. If I activate the line #define
>>> USE_P2C, I can't see any color (everything is light gray). If that line is
>>> commented, everything works as expected.
>>> Do you know what I am missing?
>>>
>>>
>>> #include <vtkSmartPointer.h>
>>> #include <vtkDataSetMapper.h>
>>> #include <vtkActor.h>
>>> #include <vtkPointDataToCellData.h>
>>> #include <vtkUnstructuredGrid.h>
>>> #include <vtkUnstructuredGridGeometryFilter.h>
>>> #include <vtkGeometryFilter.h>
>>> #include <vtkXMLUnstructuredGridReader.h>
>>> #include <vtkRenderer.h>
>>> #include <vtkRenderWindow.h>
>>> #include <vtkPointData.h>
>>> #include <vtkCellData.h>
>>> #include <vtkRenderWindowInteractor.h>
>>> int main()
>>> {
>>> // Read the grid
>>> std::string filename = "D:/model.vtu";
>>> std::string fieldname = "TEMP";
>>> vtkSmartPointer<vtkXMLUnstructuredGridReader> reader =
>>> vtkSmartPointer<vtkXMLUnstructuredGridReader>::New();
>>> reader->SetFileName(filename.c_str());
>>> reader->Update();
>>> vtkSmartPointer<vtkUnstructuredGrid> model = reader->GetOutput();
>>>
>>> vtkSmartPointer<vtkDataSetMapper> colorMapper =
>>> vtkSmartPointer<vtkDataSetMapper>::New();
>>> vtkSmartPointer<vtkActor> colorActor = vtkSmartPointer<vtkActor>::New();
>>> vtkSmartPointer<vtkGeometryFilter> geometryFilter =
>>> vtkSmartPointer<vtkGeometryFilter>::New();
>>>
>>> //============ BEGIN OF SECTION OF INTEREST
>>> // Convert point to cell data
>>> vtkSmartPointer<vtkPointDataToCellData> point2CellData =
>>> vtkSmartPointer<vtkPointDataToCellData>::New();
>>> point2CellData->PassPointDataOn();
>>> point2CellData->SetInputData(model);
>>> point2CellData->Update();
>>>
>>> #define USE_P2C
>>> #ifdef USE_P2C
>>> // Neither of these "setActiveScalars" makes any difference
>>> //model->GetCellData()->SetActiveScalars(fieldname.c_str());
>>> //model->GetPointData()->SetActiveScalars(fieldname.c_str());
>>> geometryFilter->SetInputData(point2CellData->GetOutput());
>>> geometryFilter->SetInputArrayToProcess(0, 0, 0,
>>> vtkDataObject::FIELD_ASSOCIATION_CELLS, fieldname.c_str()); // cells
>>> because I transfered the data
>>> #else
>>> model->GetPointData()->SetActiveScalars(fieldname.c_str());
>>> geometryFilter->SetInputData(model);
>>> geometryFilter->SetInputArrayToProcess(0, 0, 0,
>>> vtkDataObject::FIELD_ASSOCIATION_POINTS, fieldname.c_str());
>>> #endif
>>>
>>> colorMapper->SetInputConnection(geometryFilter->GetOutputPort());
>>>
>>> //============ END OF SECTION OF INTEREST
>>>
>>> colorMapper->SetScalarRange(297, 637); //hardcoded to reduce code length
>>> colorActor->SetMapper(colorMapper);
>>> colorMapper->ScalarVisibilityOn();
>>>
>>> // Usual rendering stuff, nothing of interest from here onwards
>>> //Create a renderer, render window, and interactor
>>> vtkSmartPointer<vtkRenderer> renderer =
>>> vtkSmartPointer<vtkRenderer>::New();
>>> vtkSmartPointer<vtkRenderWindow> renderWindow =
>>> vtkSmartPointer<vtkRenderWindow>::New();
>>> renderWindow->AddRenderer(renderer);
>>> vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
>>> vtkSmartPointer<vtkRenderWindowInteractor>::New();
>>> renderWindowInteractor->SetRenderWindow(renderWindow);
>>> //Add the actor to the scene
>>> renderer->AddActor(colorActor);
>>> renderer->SetBackground(.3, .6, .3); // Background color green
>>> //Render and interact
>>> renderWindow->Render();
>>> renderWindowInteractor->Start();
>>> return EXIT_SUCCESS;
>>> }
>>>
>>>
>>> Thank you!.
>>>
>>> 2016-02-18 17:05 GMT+01:00 Ken Martin <ken.martin at kitware.com>:
>>>
>>>> Hello Fernando,
>>>>
>>>> Making sure that I understand the issue. Essentially you have defined
>>>> scalars/colors on the points of a triangle. With phong shading the colors
>>>> interpolate across the triangle. With flat shading on the old backend, the
>>>> system takes the color of the first point and uses that for the entire
>>>> triangle. On the new backend the colors are still interpolated across the
>>>> triangle.  Is that the issue you see?
>>>>
>>>> If so, then the issue is that on the new backend I am interpreting
>>>> shading to only mean lighting and normal calculations while in the old
>>>> backend it seems to include vertex color properties (but not other
>>>> properties such as tcoords, hmm wonder what happens with flat shading and
>>>> texture based coloring) In modern OpenGL (version 3.2 ) you can specify
>>>> flat versus smooth interpolation by attribute. So normals could be flat
>>>> while colors are smooth. Without requiring OpenGL 3.2 we would need to
>>>> rebuild the VBO each time you switch between flat and smooth, basically
>>>> treating flat shading as if you had cell colors instead of point colors.
>>>>
>>>> If backward compatibility was not an issue :-) I would suggest moving
>>>> to require OpenGL 3.2 and then modifying vtkProperty so that people can
>>>> independently specify if they want normals/colors/etc to be
>>>> flat/smooth/perspective.
>>>>
>>>> One stopgap, you could use vtkPointDataToCellData to essentially
>>>> accomplish what you want in either back end.
>>>>
>>>> Thanks
>>>> Ken
>>>>
>>>>
>>>>
>>>> On Thu, Feb 18, 2016 at 10:14 AM, Fernando Nellmeldin <
>>>> f.nellmeldin at open-engineering.com> wrote:
>>>>
>>>>> Hello friends.
>>>>>
>>>>> In our application, we want to allow the user to alternate between a
>>>>> flat and a smooth shading of the colors in an actor. To do this, we have a
>>>>> option that allows the user to call setInterpolationToFlat() or
>>>>> setInterpolationToPhong() in the property of the vtkactor.
>>>>>
>>>>> The problem is that the call to set flat is not working, there is no
>>>>> change and the actor is always rendered smooth.
>>>>>
>>>>> I've tried with VTK 6.3.0 and VTK 7.0.0 under OpenGL2 backend. In VTK
>>>>> 5.10 (using the old opengl), this works as expected.
>>>>>
>>>>> And please note that in the three cases, the code is exactly the same.
>>>>> Well, except the connection between the ugrid and the geometry filter that
>>>>> I have the usual if:
>>>>> #if VTK_MAJOR_VERSION <= 5
>>>>> geometryFilter->SetInputConnection(m_model->GetProducerPort());
>>>>> #else
>>>>> geometryFilter->SetInputData(m_model);
>>>>> #endif
>>>>>
>>>>> Therefore, is the support of flat interpolation dropped, or I have to
>>>>> add something to make it work under OpenGL2 backend?
>>>>>
>>>>> Thank you!
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Powered by www.kitware.com
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>>>>>
>>>>
>>>>
>>>> --
>>>> Ken Martin PhD
>>>> Chairman & CFO
>>>> Kitware Inc.
>>>> 28 Corporate Drive
>>>> Clifton Park NY 12065
>>>> 518 371 3971
>>>>
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>>>
>>>
>>>
>>> --
>>> *Fernando NELLMELDIN*
>>> Software Engineer
>>> *_______________________________________________________________*
>>>
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>>>
>>> Rue Bois Saint-Jean 15/1
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>>
>>
>> --
>> ------------------------------------------------------------------
>> Simon Esneault
>> Rennes, France
>> ------------------------------------------------------------------
>>
>

-- 
------------------------------------------------------------------
Simon Esneault
Rennes, France
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