[vtkusers] How to create triangle strips?

[David Gobbi]

Hi Hugo,

Your code is a mix of the method that I suggested and the method that David
Doria suggested.  The SetStrips() method is a low-level method for building
a vtkPolyData (as per my suggestion).  The InsertNextCell() method is a
high-level method for building a vtkDataSet (as per David Doria's
suggestion).  You have to use one method or the other, not both.  I
apologize for the confusion.

  David

On Mon, Nov 22, 2010 at 11:10 AM, Hugo Valdebenito <hugo at maptek.cl> wrote:

> Hi David.
>
> It works with one strip, but that doesn't work with 2 o more strips. that
> is my implementation (sorry,  is C#, I translated the c++ example)
>
>        public void GenerateSurface(int nx, int ny)
>        {
>
>           vtkPoints points = vtkPoints.New();
>           vtkCellArray cells = new vtkCellArray();
>           vtkTriangleStrip triangleStrip;
>
>
>           double z,zmax = 50.0;
>           points.SetNumberOfPoints(nx * ny);
>          //se points
>           int index = 0;
>           for (int j = 0; j < ny; j++)
>           {
>              for (int i = 0; i < nx; i++)
>              {
>                 z = zmax * Math.Sin(4 * 3.1 * i / (float)nx) + 4 * j /
> (float)(ny);
>                 //insert point and increment index
>                 *points.SetPoint(index++,(double)i, (double)j, (double)z);
> *
>
>
>              }
>           }
>           //set ids
>           for (int i = 0; i < nx - 1; i++)
>           {
>              index = 0;
>              triangleStrip = new vtkTriangleStrip();
>              triangleStrip.GetPointIds().SetNumberOfIds(ny*2);
>
>               for (int j = 0; j < ny; j++)
>              {
>                 triangleStrip.GetPointIds().SetId(index++, i + j * nx);
>                 triangleStrip.GetPointIds().SetId(index++, i + j * nx + 1);
>              }
>              *cells.InsertNextCell(triangleStrip);*
>           }
>           vtkPolyData polydata = new vtkPolyData();
>           polydata.SetPoints(points);
>           *polydata.SetStrips(cells);*
>
>           // Create an actor and mapper
>           vtkDataSetMapper mapper = new vtkDataSetMapper();
>           mapper.SetInput(polydata);
>           vtkActor Actor = new vtkActor();
>
>           Actor.SetMapper(mapper);
>           Actor.GetProperty().SetRepresentationToWireframe();
>           //Add the actors to the scene
>           _renderer.AddActor(Actor);
>      }
>
>
> Hugo
>
>
>
> 2010/11/22 David Gobbi <david.gobbi at gmail.com>
>
>  Hi Hugo,
>>
>> The vtkPolyData stores the strips in an array called "Strips", that is
>> how it knows what cells are strips.  And all vtkDataSet objects have a
>> GetCellType(i) method that VTK can use to check the type of cell "i".
>> I have some code here that generates several shapes with triangle
>> strips:
>>
>> https://github.com/dgobbi/ToolCursor/blob/master/vtkGeometricCursorShapes.cxx
>>
>>  David
>>
>>
>> On Mon, Nov 22, 2010 at 5:55 AM, Hugo Valdebenito <hugo at maptek.cl> wrote:
>> >
>> > You should to see the triangles, maybe it's wrong. with 4 ids you define
>> 2
>> > triagles, with 5 --> 3 and so on (that structure saves memory). How does
>> you
>> > said to vtk that you are using Strips?  I don't know how to define that
>> on
>> > VTK.
>> >
>> >
>> > Thanks!
>> >
>> >
>> >
>> > 2010/11/19 David Doria <daviddoria at gmail.com>
>> >>
>> >> On Fri, Nov 19, 2010 at 3:22 PM, Hugo Valdebenito <hugo at maptek.cl>
>> wrote:
>> >> > Thanks david!!
>> >> >
>> >> > vtkCellArray object is defined, but never used....
>> >> >
>> >> > Anyone can suggest a fix?, I'm beginner on VTK
>> >> > Hugo
>> >>
>> >> Try it now. It doesn't show the line through the middle of the square
>> >> (the center edge of the triangles), but maybe that is expected with a
>> >> triangle strip?
>> >>
>> >>
>> >>
>> http://www.vtk.org/Wiki/VTK/Examples/Cxx/Broken/GeometricObjects/TriangleStrip
>> >>
>> >> David
>>
>
>
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