[vtkusers] Bug or Design: Rendering concave polygons with vtkActor2D

[Xiaofeng Z]

Thanks for the suggest.  I'll try vtkTriangleFilter and report the result.

Xiaofeng



> From: david.gobbi at gmail.com
> Date: Thu, 6 May 2010 09:20:40 -0600
> Subject: Re: [vtkusers] Bug or Design: Rendering concave polygons with 	vtkActor2D
> To: xf10036 at hotmail.com
> CC: dave.demarle at kitware.com; vtkusers at vtk.org
> 
> Why not use vtkTriangleFilter?  It can tesselate concave polygons.
> 
>    David
> 
> 
> On Thu, May 6, 2010 at 9:06 AM, Xiaofeng Z <xf10036 at hotmail.com> wrote:
> > David,
> >
> > I am thinking of using GLU to perform Tessellation.  I wonder how involved
> > it would be if I try to do it inside VTK.
> >
> > I would appreciate it if you can provide some insight.
> >
> > Thanks!
> >
> > Xiaofeng
> >
> >
> >
> >
> >> From: dave.demarle at kitware.com
> >> Date: Wed, 5 May 2010 07:51:40 -0400
> >> Subject: Re: [vtkusers] Bug or Design: Rendering concave polygons with
> >> vtkActor2D
> >> To: xf10036 at hotmail.com
> >> CC: vtkusers at vtk.org
> >>
> >> I suspect that is because OpenGL doesn't render concave polygons
> >> properly, thus VTK, which uses GL to render, doesn't either. So
> >> unfortunately you have to tesselate that into a set convex polygons in
> >> order to have it drawn properly.
> >>
> >> David E DeMarle
> >> Kitware, Inc.
> >> R&D Engineer
> >> 28 Corporate Drive
> >> Clifton Park, NY 12065-8662
> >> Phone: 518-371-3971 x109
> >>
> >>
> >>
> >> On Tue, May 4, 2010 at 11:38 AM, Xiaofeng Z <xf10036 at hotmail.com> wrote:
> >> > Concave polygons are not rendered as expected with vtkPolyDataMapper and
> >> > vtkActor2D (see below).  Is it by design or is it a bug?  If it's by
> >> > design,
> >> > is there any flag can be set to alter the rendering behaviour?
> >> >
> >> > Thanks!
> >> >
> >> > Xiaofeng
> >> >
> >> > Hi all,
> >> >
> >> > How do I make uniform transparency in a concave polygon, instead of
> >> > getting
> >> > multiple shades, e.g. in the attached graph?
> >> >
> >> > The polygon are created with:
> >> >
> >> > vtkPoints* points = vtkPoints::New();
> >> > vtkCellArray* cells = vtkCellArray::New();
> >> > points->SetNumberOfPoints(4);
> >> >
> >> > // create a concave polygon (equilateral with a cutout at the bottom)
> >> >
> >> > points->SetPoint(0, 10.0, 10.0, 0.0);
> >> > points->SetPoint(1, 110.0, 183.2, 0.0);
> >> > points->SetPoint(2, 210.0, 10.0, 0.0);
> >> > points->SetPoint(3, 110.0, 110.0, 0.0);
> >> > cells->Allocate(1, 5);
> >> > cells->InsertNextCell(5);
> >> > cells->InsertCellPoint(0);
> >> > cells->InsertCellPoint(1);
> >> > cells->InsertCellPoint(2);
> >> > cells->InsertCellPoint(3);
> >> > cells->InsertCellPoint(0);
> >> > vtkPolyData* poly = vtkPolyData::New();
> >> > poly->Initialize();
> >> > poly->SetGlobalWarningDisplay(1);
> >> > poly->SetPoints(points);
> >> > poly->SetPolys(cells);
> >> >
> >> > A vtkActor2D and a vtkPolyDataMapper2D was used for the rendering.
> >> >
> >> > Many thanks!
> >> > Xiaofeng
> >> >
> >> >
> >> >
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