[vtkusers] Bug in depth ordering whilst rendering

[Jeff Lee]

What os?  What drivers are you using - nvidia, or the ones shipped with the
os.  If linux, you can type glxinfo to get that information.
-J

On 11/28/07, Peter Clifton <pcjc2 at cam.ac.uk> wrote:
>
>
> On Wed, 2007-11-28 at 00:49 -0800, David Thompson wrote:
> > > Do any developers hang out here?
> > Yes.
> >
> > > I appreciate that having no reply to a question (in what is arguably a
> > > short time so far), can indicate many things..
> > >
> > > * Question asked in wrong place
> > > * Question missing information
> > > * Question containing too much information
> > >
> > > If anyone is familiar with the rendering code, perhaps they will be
> > > able
> > > to point me in the right direction.
> > Depth peeling does not appear to be in VTK 5.0.x. It is present in the
> > CVS trunk. See http://www.vtk.org/Wiki/VTK/Depth_Peeling for some
> > information on how to use it (note the list of GL extensions you need
> > in order for it to work). Shy of depth peeling,
> >
> > > I doubt this is a VTK bug in the strictest sense (as MESA software
> > > rendering seemed to "fix" it), but without knowing what underlying
> > > cause
> > > is, or having a simple gl / glut test case, reporting a MESA bug isn't
> > > yet going to get much attention either.
> > It is not a bug. Without depth peeling, geometry primitives must be
> > depth-sorted each time the camera changes. This is not a trivial
> > amount of work for large datasets and many people don't have
> > transparent geometry to render, so depth sorting is something you must
> > set up in your pipeline if you want it to be done (see
> > vtkDepthSortPolyData). Without depth sorting, you will see some
> > triangles blended into the color buffer in the wrong order. Without a
> > screen capture or more details, I would guess that is what you are
> > reporting.
>
> It does sound like it, however I "think" I'm seeing this with
> non-translucent objects too (although not in the TextureThreshold.py
> example). I can post some screen-shots, and simple Python + VTK example
> code when I'm at the lab later.
>
> I'll do some tests based on your suggestions, and get back to you. What
> is strange, is MESA software rendering clears up the bug for me in the
> case I tested (not TextureThreshold.py).
>
> This also manifests with viewer, if I toggle on the coordinate mark
> (x,y,z lines with cones pointing in their directions). The coordinate
> arrows end up drawn in the wrong Z order. (Would I need to sort the poly
> data for these to draw correctly too?)
>
> I'm also trying to build the CVS head of VTK, as if depth peeling solves
> the issue, I'll be sorted.
>
> As its a complex piece of software, I'm trying to build it as a debian
> package so I can just dpkg --install it to replace the current version
> I've got installed without fear of breaking my system. The package
> building process makes any build failures much more time-consuming to
> fix though!
>
> Many thanks,
>
> --
> Peter Clifton
>
> Electrical Engineering Division,
> Engineering Department,
> University of Cambridge,
> 9, JJ Thomson Avenue,
> Cambridge
> CB3 0FA
>
> Tel: +44 (0)7729 980173 - (No signal in the lab!)
>
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