[vtkusers] [vtk-developers] How to use color mapping for vtkPistonMapper?

Wed Dec 4 10:04:27 EST 2013

nice animation JB!

On Wed, Dec 4, 2013 at 7:38 AM, Biddiscombe, John A. <biddisco at cscs.ch>wrote:

> Just noticed a mistake in my text after clicking send ...
>
> Erratum : "Decided on Depth Sorting" - instead of depth peeling.
>
> > -----Original Message-----
> > From: Biddiscombe, John A.
> > Sent: 04 December 2013 13:35
> > To: Biddiscombe, John A.; David E DeMarle; Enya Shen
> > Cc: vtkdev; vtkusers at vtk.org
> > Subject: RE: [vtkusers] [vtk-developers] How to use color mapping for
> > vtkPistonMapper?
> >
> > https://hpcforge.org/scm/browser.php?group_id=117
> > is a project called pv-zoltan
> >
> > I needed to do transparent rendering of neuron circuits which are very
> large
> > and complex, depth peeling is one option, but for some of these circuits
> I had
> > to use a machine with no graphics capabilities, so I wanted a software
> render
> > option and decided on depth peeling. see
> > ftp://ftp.cscs.ch/out/biddisco/bbp/videos/5k-voltage-differentials.aviskip to
> > about 45 seconds in for an example of the data that is interesting -
> it's just
> > under 1 billion triangles, rendered in parallel. Some of the scenes are
> very
> > complex, so for depth peeling, you really need hundreds of layers to be
> sure
> > it's perfect (though nobody would be able to tell the difference).
> >
> > What is pv-zoltan : it's a set of classes to allow parallel mesh
> redistribution
> > using the zoltan library from trilinos. Once the mesh is partitioned, I
> then
> > depth sort the triangles and render in parallel with sort last
> compositing.
> > 1) There is a custom depth sort class in the code which generates a depth
> > sorted ID list and attaches it to the dataset, then a custom
> > vtkPolyDataMapper/Painter which renders using the sorted order (this
> > differs from the vtkDepthSortPolyData in vtk which actually sorts the
> > polygons (and all cell/point arrays)  and effectively doubles the memory
> use,
> > then renders with the normal polydatamapper/painter).  By generating an
> Id
> > ordering and then painting in that order, we only add 1 int per cell.
> > 2) mesh partitioning with zoltan - and some enhancements to the rendering
> > front end to bypass the default compositing in paraview and use the
> KdTree
> > from zoltan to do the ordered compositing.
> > 3) Once that was working, I wanted to try to do the depth sort on the
> GPU,
> > so I looked at piston and found it to be very easy to modify to suit my
> needs.
> > I have changed the vtkDataSetToPiston class and the vtkPistonMapper
> > slightly (and the code will only work with triangle based geometry
> unless you
> > uncomment the triangulation routine somewhere). When the PISTON code
> > is enabled, the CPU depth sort is disabled (point 1 above) and instead
> push
> > the dataset to GPU, do depth sort on the fly (some thrust code thrown in
> > using thrust::sort_by_key<> and a distance functor) and render in one
> pass
> > effectively. (two loops, but only one render pass).
> > 4) There is some code in the colorGPU branch which activates the colour
> > table lookup and generation on the GPU as well, but I didn't get time to
> look
> > at it this morning to remind myself of what happens where and when. I
> seem
> > to recall I have a small bug in there which makes the table get
> regenerated
> > more often than it needs to. And possibly more CPU-GPU traffic than
> strictly
> > necessary, but nothing serious.
> > 5) Because the transparent rendering uses per vertex opacity - instead of
> > using a scalars to colours, we use a new two scalars to colours
> (originally
> > written for the point sprite renderer), this takes one array for scalars
> and one
> > for opacity, so the lookup stuff is a bit more versatile than the
> standard.
> > 6) Everything is handled (rather smoothly I think, even if I do say so
> myself)
> > by the DepthSortRepreseantation which connects everything together. It
> > just needs a couple of small fixes for paraview to get working, but most
> of it
> > should compile ok and work - except for the ordered compositing which
> > requires some extra info passed via the vtkBoundsExtentTranslator in the
> > plugin which holds the region assignments generated by Zoltan and is
> used to
> > send the KdTree to the compositing code in the front end.
> >
> > .... currently my depth sort branch is out of date/order, so I won't
> paste a
> > paraview patch. You'd need to just comment out a couple of lines of the
> > plugin code. I'd suggest looking  at the piston stuff and having a play
> with it. I
> > can't remember if I added an option to disable the depth sort and only
> do the
> > render on the GPU, the interesting part is where the cuda array handles
> are
> > passed from the dataset after sorting etc and given to OpenGL for
> rendering,
> > most of the piston code itself is irrelevant and it's only the push to
> gpu and
> > pass of handles to GL that is interesting. Many thanks to the original
> Piston
> > developers for showing how to do it.
> >
> > NB. running on a single process ought to work, but there may be a gotcha
> I've
> > forgotten about. when I have a few hours spare I'll apply my patches to
> my
> > current paraview tree and see if everything is still working ok and post
> an
> > update.
> >
> > JB
> >
> >
> > > -----Original Message-----
> > > From: vtkusers-bounces at vtk.org [mailto:vtkusers-bounces at vtk.org] On
> > > Behalf Of Biddiscombe, John A.
> > > Sent: 03 December 2013 15:44
> > > To: David E DeMarle; Enya Shen
> > > Cc: vtkdev; vtkusers at vtk.org
> > > Subject: Re: [vtkusers] [vtk-developers] How to use color mapping for
> > > vtkPistonMapper?
> > >
> > > Yes. I've enhanced the piston mapper and done the lookuptable on the
> > GPU.
> > > I'm stuck in a terminally dull meeting right now, but once I escape,
> > > I'll brush off the code and post a link.
> > >
> > > JB
> > >
> > > From: David DeMarle
> > > <dave.demarle at kitware.com<mailto:dave.demarle at kitware.com>>
> > > Date: Tuesday 3 December 2013 14:47
> > > To: Enya Shen
> > > <enya.shen2010 at gmail.com<mailto:enya.shen2010 at gmail.com>>
> > > Cc: VTK Developers <vtk-developers at vtk.org<mailto:vtk-
> > > developers at vtk.org>>, "vtkusers at vtk.org<mailto:vtkusers at vtk.org>"
> > > <vtkusers at vtk.org<mailto:vtkusers at vtk.org>>
> > > Subject: Re: [vtk-developers] How to use color mapping for
> > > vtkPistonMapper?
> > >
> > > Unfortunately I ran out of time and didn't get around to moving VTK's
> > > lookup table over when I originally implemented that class. So, the
> > > randow color map you see now is the only option when doing direct GPU
> > > to GPU rendering. Unless you hack the class yourself to make the
> > > transfer function configurable of course.
> > >
> > > If anyone out there has an updated implementation (ahem John B.)
> > > please direct us to it and we can see about folding your improvements
> in.
> > >
> > > thanks
> > >
> > >
> > > David E DeMarle
> > > Kitware, Inc.
> > > R&D Engineer
> > > 21 Corporate Drive
> > > Clifton Park, NY 12065-8662
> > > Phone: 518-881-4909
> > >
> > >
> > > On Tue, Dec 3, 2013 at 12:24 AM, Enya Shen
> > > <enya.shen2010 at gmail.com<mailto:enya.shen2010 at gmail.com>> wrote:
> > > Dear all,
> > >
> > > I try to use vtkPistonMapper, but when I set the color with
> > > setColor(double[3]), I got nothing changed.
> > >
> > > Thanks for any example or advice!
> > >
> > > Regards,
> > > Enya
> > >
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