[vtkusers] Displaying a simple non convex polygon

[Ulrich Kemloh]

Dear VTK users,

I am having some troubles displaying a simple non convex polygon.
There are at least two triangles strips out of nowhere which seem to be connected to the first vertex.
Attached is the code and the output. 

It is quite simple, so I guess I might be doing something terribly wrong, 
or I am missing some fundamental knowledge about vtk.
As far as I know vtkPolygon handles non convex polygons as well. 
the Vertex should just be counter-clockwise.

Any hints will be so highly appreciated.

Viele Grüße
Ulrich



Minimal working sample Code:


#include <vtkVersion.h>
#include <vtkSmartPointer.h>
#include <vtkPolygon.h>
#include <vtkCellArray.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkActor.h>
#include <vtkRenderWindow.h>
#include <vtkRenderer.h>
#include <vtkRenderWindowInteractor.h>

int main(int, char *[])
{
    // Setup four points
    vtkSmartPointer<vtkPoints> points =
            vtkSmartPointer<vtkPoints>::New();
    points->InsertNextPoint(-5, 3, 0.0 );
    points->InsertNextPoint( 0, 3, 0.0 );
    points->InsertNextPoint( 0, 1, 0.0 );
    points->InsertNextPoint( -5, 1, 0.0 );
    points->InsertNextPoint( -5, -3, 0.0 );
    points->InsertNextPoint( 0, -3, 0.0 );
    points->InsertNextPoint( 2, -3, 0.0 );
    points->InsertNextPoint( 18, -3, 0.0 );
    points->InsertNextPoint( 20, -3, 0.0 );
    points->InsertNextPoint( 25, -3, 0.0 );
    points->InsertNextPoint( 25, 1, 0.0 );
    points->InsertNextPoint( 20, 1, 0.0 );
    points->InsertNextPoint( 20, 3, 0.0 );
    points->InsertNextPoint( 25, 3, 0.0 );
    points->InsertNextPoint( 25, 7, 0.0 );
    points->InsertNextPoint( -5, 7, 0.0 );
    // Create the polygon
    vtkSmartPointer<vtkPolygon> polygon =
            vtkSmartPointer<vtkPolygon>::New();
    polygon->GetPointIds()->SetNumberOfIds(15);
    polygon->GetPointIds()->SetId(0, 0);
    polygon->GetPointIds()->SetId(1, 1);
    polygon->GetPointIds()->SetId(2, 2);
    polygon->GetPointIds()->SetId(3, 3);
    polygon->GetPointIds()->SetId(4, 4);
    polygon->GetPointIds()->SetId(5, 5);
    polygon->GetPointIds()->SetId(6, 6);
    polygon->GetPointIds()->SetId(7, 7);
    polygon->GetPointIds()->SetId(8, 8);
    polygon->GetPointIds()->SetId(9, 9);
    polygon->GetPointIds()->SetId(10, 10);
    polygon->GetPointIds()->SetId(11, 11);
    polygon->GetPointIds()->SetId(12, 13);
    polygon->GetPointIds()->SetId(13, 13);
    polygon->GetPointIds()->SetId(14, 14);
    polygon->GetPointIds()->SetId(15, 15);
    //polygon->GetPointIds()->SetId(16, 16);
    // Add the polygon to a list of polygons

    vtkSmartPointer<vtkCellArray> polygons =
            vtkSmartPointer<vtkCellArray>::New();
    polygons->InsertNextCell(polygon);
    // Create a PolyData
    vtkSmartPointer<vtkPolyData> polygonPolyData =
            vtkSmartPointer<vtkPolyData>::New();
    polygonPolyData->SetPoints(points);
    polygonPolyData->SetPolys(polygons);
    // Create a mapper and actor
    vtkSmartPointer<vtkPolyDataMapper> mapper =
            vtkSmartPointer<vtkPolyDataMapper>::New();
#if VTK_MAJOR_VERSION <= 5
    mapper->SetInput(polygonPolyData);
#else
    mapper->SetInputData(polygonPolyData);
#endif
    vtkSmartPointer<vtkActor> actor =
            vtkSmartPointer<vtkActor>::New();
    actor->SetMapper(mapper);
    // Visualize
    vtkSmartPointer<vtkRenderer> renderer =
            vtkSmartPointer<vtkRenderer>::New();
    vtkSmartPointer<vtkRenderWindow> renderWindow =
            vtkSmartPointer<vtkRenderWindow>::New();
    renderWindow->AddRenderer(renderer);
    vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
            vtkSmartPointer<vtkRenderWindowInteractor>::New();
    renderWindowInteractor->SetRenderWindow(renderWindow);
    renderer->AddActor(actor);
    renderer->SetBackground(.5,.3,.31); // Background color salmon
    renderWindow->Render();
    renderWindowInteractor->Start();
    return EXIT_SUCCESS;
}

-- 
Ulrich Kemloh
Division Civil Security and Traffic
Jülich Supercomputing Centre
Institute for Advanced Simulation
tel +49 2461 61 4193
fax +49 2461 61 6656
www.fz-juelich.de/ias/jsc/cst 



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