Problem with polydatas sharing vtkPoints in vtk8

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Problem with polydatas sharing vtkPoints in vtk8

Tiago Nobrega
Hi,

I'm trying to update from vtk 7.0 and I'm having an issue with a particular setup of polydatas. In my case I have a single vtkPoints that is shared by multiple vtkPolydatas, where each polydata renders a different set of cells. I can't get the rendering to show more than one polydata at a time in vtk 8.0 and up, but it works as expected in vtk 7.1. In all cases I am using the new OpenGL2 backend.

I created a minimal example that reproduces the issue for me: https://gist.github.com/tigarmo/c90ff07a1b63bbcf396fa4aaf1e824a9 . It tries to show 2 quads, where each quad is a cell in a different polydata, but both polydatas share the same vtkPoints. This shows 2 quads as expected (by me) in vtk 7.1 but only 1 quad in vtk 8.0.1, 8.1.0 and 8.1.1. A surprising detail is that which quad is shown varies depending on the run. Sometimes it's the left one, sometimes the right one.

Does anyone have any suggestions? Is this a bug? Could it be related to improvements in VBO caching that I saw in 8.0's changelog?

Thank you for your time,

Tiago Nobrega

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Re: Problem with polydatas sharing vtkPoints in vtk8

Sean McBride
On Thu, 24 Jan 2019 10:28:07 -0200, Tiago Nobrega said:

>I'm trying to update from vtk 7.0 and I'm having an issue with a particular
>setup of polydatas. In my case I have a single vtkPoints that is shared by
>multiple vtkPolydatas, where each polydata renders a different set of
>cells. I can't get the rendering to show more than one polydata at a time
>in vtk 8.0 and up, but it works as expected in vtk 7.1. In all cases I am
>using the new OpenGL2 backend.
>
>I created a minimal example that reproduces the issue for me:
>https://gist.github.com/tigarmo/c90ff07a1b63bbcf396fa4aaf1e824a9 . It tries
>to show 2 quads, where each quad is a cell in a different polydata, but
>both polydatas share the same vtkPoints. This shows 2 quads as expected (by
>me) in vtk 7.1 but only 1 quad in vtk 8.0.1, 8.1.0 and 8.1.1. A surprising
>detail is that which quad is shown varies depending on the run. Sometimes
>it's the left one, sometimes the right one.
>
>Does anyone have any suggestions? Is this a bug? Could it be related to
>improvements in VBO caching that I saw in 8.0's changelog?

Tiago,

Since no one seems to have a better answer for you, what you could do is use 'git bisect' to find exactly which commit between 7.1 and 8.0 caused this change in behaviour.  The commit message will hopefully shed light on the cause and whether it's a bug or not.

Cheers,

--
____________________________________________________________
Sean McBride, B. Eng                 [hidden email]
Rogue Research                        www.rogue-research.com
Mac Software Developer              Montréal, Québec, Canada


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Re: Problem with polydatas sharing vtkPoints in vtk8

Tiago Nobrega
Hi Sean,

Thanks for the reply. I'll try bisecting once I get some free time, for now I suppose I'll just stay with 7.1.
I've also reported this bug on Gitlab: https://gitlab.kitware.com/vtk/vtk/issues/17508 . I'll update the report if I get any progress.

Tiago

On Wed, Jan 30, 2019 at 3:20 PM Sean McBride <[hidden email]> wrote:
On Thu, 24 Jan 2019 10:28:07 -0200, Tiago Nobrega said:

>I'm trying to update from vtk 7.0 and I'm having an issue with a particular
>setup of polydatas. In my case I have a single vtkPoints that is shared by
>multiple vtkPolydatas, where each polydata renders a different set of
>cells. I can't get the rendering to show more than one polydata at a time
>in vtk 8.0 and up, but it works as expected in vtk 7.1. In all cases I am
>using the new OpenGL2 backend.
>
>I created a minimal example that reproduces the issue for me:
>https://gist.github.com/tigarmo/c90ff07a1b63bbcf396fa4aaf1e824a9 . It tries
>to show 2 quads, where each quad is a cell in a different polydata, but
>both polydatas share the same vtkPoints. This shows 2 quads as expected (by
>me) in vtk 7.1 but only 1 quad in vtk 8.0.1, 8.1.0 and 8.1.1. A surprising
>detail is that which quad is shown varies depending on the run. Sometimes
>it's the left one, sometimes the right one.
>
>Does anyone have any suggestions? Is this a bug? Could it be related to
>improvements in VBO caching that I saw in 8.0's changelog?

Tiago,

Since no one seems to have a better answer for you, what you could do is use 'git bisect' to find exactly which commit between 7.1 and 8.0 caused this change in behaviour.  The commit message will hopefully shed light on the cause and whether it's a bug or not.

Cheers,

--
____________________________________________________________
Sean McBride, B. Eng                 [hidden email]
Rogue Research                        www.rogue-research.com
Mac Software Developer              Montréal, Québec, Canada



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