[vtkusers] How to pass a triangle without its point set?

[David Doria]

On Sat, Oct 24, 2009 at 12:13 PM, Bill Lorensen <bill.lorensen at gmail.com> wrote:
> Try this:
> #include "vtkSmartPointer.h"
> #include "vtkTriangle.h"
> #include "vtkPoints.h"
>
> void TriangleInfo ( vtkTriangle* Triangle );
>
> main (int, char*[])
> {
>
>  vtkSmartPointer<vtkTriangle> triangle = vtkSmartPointer<vtkTriangle>::New();
>  triangle->GetPointIds()->SetId ( 0, 0 );
>  triangle->GetPointIds()->SetId ( 1, 1 );
>  triangle->GetPointIds()->SetId ( 2, 2 );
>
>  triangle->GetPoints()->InsertPoint ( 0, 1.0, 2.0, 3.0 );
>  triangle->GetPoints()->InsertPoint ( 1, 4.0, 5.0, 6.0 );
>  triangle->GetPoints()->InsertPoint ( 2, 7.0, 8.0, 9.0 );
>
>
>  TriangleInfo(triangle);
>  return EXIT_SUCCESS;
> }
>
> void TriangleInfo ( vtkTriangle* Triangle )
> {
>  vtkPoints* Points = Triangle->GetPoints();
>
>  for ( unsigned int i = 0; i < 3; i++ )
>    {
>    double p[3];
>    Points->GetPoint ( i,p );
>    std::cout << "p" << i << ": " << p[0] << " " << p[1] << " " << p[2]
>              << std::endl;
>    }
> }


Yea, that works.  Can you explain a little bit about what is going on?
The way I had done it, I thought SetPoints() was doing the same thing
as what you've done here with InsertPoint(...)? Is this actually
demonstrating two very different functionalities?: 1) the ability to
have a bunch of triangles that simply index into a giant point list
and 2) the ability to have a triangle which actually contains the data
about itself?

Also, I changed Your InsertPoint calls to SetPoint with the same
arguments and it still worked. That seems more intuitive to me, as it
makes it seem like the triangle already has 3 slots for points and you
just have to set them. I thought "Insert*" was always for when you
wanted to add to a list, like an "InsertNext*"? What does it mean to
Insert into an already existing slot, as done here with InsertPoint(0,
...)? How is it different than SetPoint(0,...)?

Thanks for your help,

David