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David,<BR>
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I am thinking of using GLU to perform Tessellation. I wonder how involved it would be if I try to do it inside VTK.<BR>
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I would appreciate it if you can provide some insight.<BR>
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Thanks! <BR><BR>Xiaofeng<BR><BR><BR><BR> <BR>> From: dave.demarle@kitware.com<BR>> Date: Wed, 5 May 2010 07:51:40 -0400<BR>> Subject: Re: [vtkusers] Bug or Design: Rendering concave polygons with vtkActor2D<BR>> To: xf10036@hotmail.com<BR>> CC: vtkusers@vtk.org<BR>> <BR>> I suspect that is because OpenGL doesn't render concave polygons<BR>> properly, thus VTK, which uses GL to render, doesn't either. So<BR>> unfortunately you have to tesselate that into a set convex polygons in<BR>> order to have it drawn properly.<BR>> <BR>> David E DeMarle<BR>> Kitware, Inc.<BR>> R&D Engineer<BR>> 28 Corporate Drive<BR>> Clifton Park, NY 12065-8662<BR>> Phone: 518-371-3971 x109<BR>> <BR>> <BR>> <BR>> On Tue, May 4, 2010 at 11:38 AM, Xiaofeng Z <xf10036@hotmail.com> wrote:<BR>> > Concave polygons are not rendered as expected with vtkPolyDataMapper and<BR>> > vtkActor2D (see below). Is it by design or is it a bug? If it's by design,<BR>> > is there any flag can be set to alter the rendering behaviour?<BR>> ><BR>> > Thanks!<BR>> ><BR>> > Xiaofeng<BR>> ><BR>> > Hi all,<BR>> ><BR>> > How do I make uniform transparency in a concave polygon, instead of getting<BR>> > multiple shades, e.g. in the attached graph?<BR>> ><BR>> > The polygon are created with:<BR>> ><BR>> > vtkPoints* points = vtkPoints::New();<BR>> > vtkCellArray* cells = vtkCellArray::New();<BR>> > points->SetNumberOfPoints(4);<BR>> ><BR>> > // create a concave polygon (equilateral with a cutout at the bottom)<BR>> ><BR>> > points->SetPoint(0, 10.0, 10.0, 0.0);<BR>> > points->SetPoint(1, 110.0, 183.2, 0.0);<BR>> > points->SetPoint(2, 210.0, 10.0, 0.0);<BR>> > points->SetPoint(3, 110.0, 110.0, 0.0);<BR>> > cells->Allocate(1, 5);<BR>> > cells->InsertNextCell(5);<BR>> > cells->InsertCellPoint(0);<BR>> > cells->InsertCellPoint(1);<BR>> > cells->InsertCellPoint(2);<BR>> > cells->InsertCellPoint(3);<BR>> > cells->InsertCellPoint(0);<BR>> > vtkPolyData* poly = vtkPolyData::New();<BR>> > poly->Initialize();<BR>> > poly->SetGlobalWarningDisplay(1);<BR>> > poly->SetPoints(points);<BR>> > poly->SetPolys(cells);<BR>> ><BR>> > A vtkActor2D and a vtkPolyDataMapper2D was used for the rendering.<BR>> ><BR>> > Many thanks!<BR>> > Xiaofeng<BR>> ><BR>> ><BR>> ><BR>> > ________________________________<BR>> > The New Busy think 9 to 5 is a cute idea. Combine multiple calendars with<BR>> > Hotmail. Get busy.<BR>> > ________________________________<BR>> > Hotmail has tools for the New Busy. Search, chat and e-mail from your inbox.<BR>> > Learn more.<BR>> > _______________________________________________<BR>> > Powered by www.kitware.com<BR>> ><BR>> > Visit other Kitware open-source projects at<BR>> > http://www.kitware.com/opensource/opensource.html<BR>> ><BR>> > Please keep messages on-topic and check the VTK FAQ at:<BR>> > http://www.vtk.org/Wiki/VTK_FAQ<BR>> ><BR>> > Follow this link to subscribe/unsubscribe:<BR>> > http://www.vtk.org/mailman/listinfo/vtkusers<BR>> ><BR>> ><BR>                                            <br /><hr />The New Busy think 9 to 5 is a cute idea. Combine multiple calendars with Hotmail. <a href='http://www.windowslive.com/campaign/thenewbusy?tile=multicalendar&ocid=PID28326::T:WLMTAGL:ON:WL:en-US:WM_HMP:042010_5' target='_new'>Get busy.</a></body>
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