[vtkusers] Flat interpolation under OpenGL2 backend

Mon Feb 22 07:23:11 EST 2016

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
>>
>> Visit other Kitware open-source projects at
>> http://www.kitware.com/opensource/opensource.html
>>
>> Please keep messages on-topic and check the VTK FAQ at:
>> http://www.vtk.org/Wiki/VTK_FAQ
>>
>> Search the list archives at: http://markmail.org/search/?q=vtkusers
>>
>> Follow this link to subscribe/unsubscribe:
>> http://public.kitware.com/mailman/listinfo/vtkusers
>>
>>
>
>
> --
> Ken Martin PhD
> Chairman & CFO
> Kitware Inc.
> 28 Corporate Drive
> Clifton Park NY 12065
> 518 371 3971
>
> This communication, including all attachments, contains confidential and
> legally privileged information, and it is intended only for the use of the
> addressee.  Access to this email by anyone else is unauthorized. If you are
> not the intended recipient, any disclosure, copying, distribution or any
> action taken in reliance on it is prohibited and may be unlawful. If you
> received this communication in error please notify us immediately and
> destroy the original message.  Thank you.
>

-- 
*Fernando NELLMELDIN*
Software Engineer
*_______________________________________________________________*

*Open Engineering s.a.*

Rue Bois Saint-Jean 15/1
B-4102 Seraing (Belgium)
Tel: +32.4.353.30.34

http://www.open-engineering.com
https://www.linkedin.com/company/open-engineering?trk=biz-companies-cym

*_________________________________________________________________________*
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://public.kitware.com/pipermail/vtkusers/attachments/20160222/083a987b/attachment.html>