[vtkusers] VTK pipeline & rendering strategies

[Andrea Gavana]

Hi Ken,

Thank you for your answer. So it seems to me that I should not call
grid.Modified() if I only change the scalars? In my script there is almost
no pipeline, I.e. I have:

Grid --> Mapper --> Actor

No filters, no updating, no nothing.

I will try your loop example tomorrow from my work computer. Also, how can
I know if the rendering engine is using the GPU? I have a fairly powerful
machine at work, able to run commercial 3D visualization software (on a
geological scale) with multi-million cells with no problem...

Thank you again!

Andrea.

On Tue, 29 Nov 2016 at 16:37, Ken Martin <ken.martin at kitware.com> wrote:

>
> The timing are all taken after the first rendering. I have a little GUI
> with a VTK render window and a single button. Every time I press the button
> new data is randomly generated and I time the rendering only process, i.e.:
>
>
> VTK with OpenGL2 can render 500 million cells/second on a laptop GPU. If
> you are seeing performance significantly off from that and think you are
> using a GPU then something is wrong. To do timings do not rely on
> GetLastRenderTimeInSeconds but rather time a render loop like ala
>
> startTimer
> for (i = 0; i < 500; i++)
> {
>  renWin->Render();
> }
> endTimer
> print elapsedTime/500;
>
>
>
> grid.GetCellData().SetScalars(data)
> grid.Modified()
> renwin.Render()
>
>
> The render above is a first render, in that it is the first render after
> you modified your data. The entire
> pipeline has to be run then. You are probably timing how has the pipeline
> can be modified and recalaculated when you change your data.
>
>
>
> And I have a little rendering listener setup like this:
>
>
>         renderer.AddObserver(vtk.vtkCommand.EndEvent, self.OnEndEvent)
>
>
>     def OnEndEvent(self, caller, dummy1=None, dummy2=None, dummy3=None):
>
>         timeInSeconds = caller.GetLastRenderTimeInSeconds()
>         fps = 1.0/timeInSeconds
>         print timeInSeconds, fps
>
>
> However, I realized that the simulator outputs the grid with a lot of
> redundant information - i.e., duplicated points. So I did the following:
>
>         clean = vtk.vtkExtractUnstructuredGrid()
>         clean.SetInputData(grid.GetOutput())
>         clean.MergingOn()
>         clean.CellClippingOn()
>
>         clean.SetCellMinimum(0)
>         clean.SetCellMaximum(nx*ny*nz)
>         clean.Update()
>
>
> the "clean" grid contains far far far less points than the original one
> (as the coincident points have been merged), and the rendering is much
> faster - about 0.24 seconds or 4.2 fps. Now, if there was a way to tell the
> rendering engine to ignore the points (i.e., don't render the points, I
> only care about the cells...) that would be even better :-) .
>
>
> Thank you again for all your hints.
>
> Andrea.
>
>
>
>
>
>
>
>
>
>
>
> On Tue, Nov 29, 2016 at 3:39 AM, Andrea Gavana <andrea.gavana at gmail.com>
> wrote:
>
> Dear All,
>
>
> On 28 November 2016 at 16:12, Andrea Gavana <andrea.gavana at gmail.com>
> wrote:
>
> Hi David,
>
>     thank you for your answer. I will put some more comments inline too.
> Any insight or suggestion is more than welcome.
>
> On 28 November 2016 at 15:40, David E DeMarle wrote:
>
> Responses inline. Mostly though, make sure you are using the "OpenGL2"
> rendering backend, which is the default for 7.0 and 7.1.
>
>
>
> I am using VTK 7.0 through the Python bindings (the official ones from the
> Kitware website here:
>
> http://www.vtk.org/download/
>
>
> So I was assuming that the rendering backend was already OpenGL2... is
> there any way to check if this is really the case?
>
> Also, I have tried to load my dataset in ParaView, and ParaView seems to
> be doing some kind of black magic on my vtkUnstructuredGrid as I get these
> kind of messages when I load the vtk file:
>
> Warning: In
> C:\bbd\df0abce0\source-paraview\VTK\Rendering\VolumeOpenGL2\vtkOpenGLProjectedTetrahedraMapper.cxx,
> line 251
>
> vtkOpenGLProjectedTetrahedraMapper (000000000D3CAA60): Missing FBO
> support. The algorithm may produce visual artifacts.
>
>
>
>
> Which, I believe, is telling me that ParaView is not doing what I am doing
> but maybe using some kind of volume-based rendering - when I rotate the
> grid the (almost cube-shaped) cells becomes subdivided in small triangles,
> when I stop interacting with them they go back to their normal appearance.
> It would be nice to know what ParaView is doing though, and also what "FBO
> support" means :-). I also noticed that ParaView is slightly faster in
> changing the displayed property - maybe 2 or 3 times faster than my
> bare-bone script.
>
>
>
>
> Just to add some more information: it is true that ParaView is faster in
> the re-rendering when I switch to another property, but it also shows heavy
> visual artifacts (i.e., cells with multiple colors in them?!? - see
> attached screenshot). So, if I understood it correctly, ParaView uses some
> kind of volume rendering of my vtkUnstructuredGrid (although I didn't ask
> it to... should it not use the default vtkDataSetMapper?).
>
> Based on my original pipeline:
>
> vtkUnstructuredGrid --> vtkThreshold --> vtkDataSetMapper --> vtkActor
>
> I have tried everything I know to speed up the re-rendering of the grid, I
> actually operate directly on the output of vtkThreshold (that is still a
> vtkUnstructuredGrid), so I simply throw away the original grid. With and
> without ImmediateModeRendering, with and without backface culling. My best
> improvements so far took the rendering time from 1.04 seconds to 0.94
> seconds... so not much of an improvement :-) .
>
> I am of course open to any suggestions anyone may have on the rendering
> part - assuming that my geometry is fixed (it is not, but I'll worry about
> that later...), basically only on the process:
>
> vtkUnstructuredGrid.SetScalars(my_data)
> vtkUnstructuredGrid.Modified()
> vtkRenderWindow.Render()
>
> And of course - if there are other visualization strategies I may use,
> please shout :-)
>
> Thank you.
>
> Andrea.
>
>
>
>
>
>
>
>
>
> On Mon, Nov 28, 2016 at 7:35 AM, Andrea Gavana <andrea.gavana at gmail.com>
> wrote:
>
> Dear All,
>
>      I am working with some stuff coming out of CFD simulations, and in
> the current work the simulator produces a 3D grid (unstructured grid made
> of hexahedrons). The full grid is about 4 million cells, but due to other
> settings in the simulator the number of "active" cells in the simulation
> ends up being "only" 270,000. In order to visualize all this, I create a
> vtkUnstructuredGrid to hold the full grid, use a vtkThreshold to remove the
> "inactive" cells and then use a vtkDataSetMapper to visualize the resulting
> active grid:
>
> vtkUnstructuredGrid --> vtkThreshold --> vtkDataSetMapper --> vtkActor
>
> However, the rendering speed for the 270,000 cells grid is quite low - it
> takes about one second to display a new property by using SetScalars on the
> output of vtkThreshold. So I thought of using a vtkDataSetSurfaceFilter on
> the output of vtkThreshold to try and speed up the rendering. So, the
> current visualization strategy I have implemented is the following:
>
> vtkUnstructuredGrid --> vtkThreshold --> vtkDataSetSurfaceFilter -->
> vtkPolyDataMapper --> vtkActor
>
> This is still as slow as my first approach, and I also have a couple of
> questions - which stems from my ignorance in VTK things:
>
>
> DataSetMapper internally does vtkDataSetSurfaceFilter->vtkPolyDataMapper
> when given something other than PolyData, so not surprising that it isn't
> faster.
>
>
> 1. When I load (from the simulator outputs) a new property (cell-based)
> and I assign its values to the original vtkUnstructuredGrid (by using
> SetScalars on it), do all the filters (vtkThreshold and
> vtkDataSetSurfaceFilter) need to be re-run? If yes, why? I am not changing
> the active/inactive cells nor the geometry of the grid, only assigning
> different scalars. And, if yes, is there any way to tell the pipeline:
> "look, I've only changed the scalars, there's no need to re-run all the
> thresholds and surface filters *again*"?
>
>
> Yes they do, since the Executive classes' Modified time tracking is not
> fine grained enough to know the difference, and few if any of the filters
> would know how to update just the changed portions.
>
>
> 2. Is there any other pipeline style or visualization technique in VTK or
> any settings whatsoever that could bring down the rendering time (memory is
> not that much of a concern)? Basically, what I have a the moment - in terms
> of timing - is as follows:
>
>
> Yes, use OpenGL"2". Modern OpenGL programming techniques make it up to
> hundreds of times faster than the Legacy fixed function "OpenGL" backend.
>
>
> Reading data from simulator: 0.042 seconds
> Create VTK array with data : 0.002 seconds
> Call to SetScalars         : 0.000 seconds
> Create Lookup Table        : 0.001 seconds
> Render on screen           : about 1 second
>
>
> Thank you in advance for any suggestion, my apologies for the long message.
>
> Andrea.
>
> _______________________________________________
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at
> http://www.kitware.com/opensource/opensource.html
>
> Please keep messages on-topic and check the VTK FAQ at:
> http://www.vtk.org/Wiki/VTK_FAQ
>
> Search the list archives at: http://markmail.org/search/?q=vtkusers
>
> Follow this link to subscribe/unsubscribe:
> http://public.kitware.com/mailman/listinfo/vtkusers
>
>
>
>
>
> _______________________________________________
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at
> http://www.kitware.com/opensource/opensource.html
>
> Please keep messages on-topic and check the VTK FAQ at:
> http://www.vtk.org/Wiki/VTK_FAQ
>
> Search the list archives at: http://markmail.org/search/?q=vtkusers
>
> Follow this link to subscribe/unsubscribe:
> http://public.kitware.com/mailman/listinfo/vtkusers
>
>
>
>
> --
> Ken Martin PhD
> Chairman & CFO
> Kitware Inc.
> 28 Corporate Drive
> Clifton Park NY 12065
> 518 371 3971
>
> This communication, including all attachments, contains confidential and
> legally privileged information, and it is intended only for the use of the
> addressee.  Access to this email by anyone else is unauthorized. If you are
> not the intended recipient, any disclosure, copying, distribution or any
> action taken in reliance on it is prohibited and may be unlawful. If you
> received this communication in error please notify us immediately and
> destroy the original message.  Thank you.
>
>
>
>
>
> --
> Ken Martin PhD
> Chairman & CFO
> Kitware Inc.
> 28 Corporate Drive
> Clifton Park NY 12065
> 518 371 3971
>
> This communication, including all attachments, contains confidential and
> legally privileged information, and it is intended only for the use of the
> addressee.  Access to this email by anyone else is unauthorized. If you are
> not the intended recipient, any disclosure, copying, distribution or any
> action taken in reliance on it is prohibited and may be unlawful. If you
> received this communication in error please notify us immediately and
> destroy the original message.  Thank you.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://public.kitware.com/pipermail/vtkusers/attachments/20161129/552f7dc2/attachment.html>