[vtkusers] How to create triangle strips?

[Hugo Valdebenito]

Hi David.

Thanks for you help, I'm trying to undestand, I have some doubts yet,  Which
is the difference between both methods?  Wich is better?.

Hugo.


2010/11/22 David Gobbi <david.gobbi at gmail.com>

> 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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