[vtkusers] transparent 3D over 2D

[David Gobbi]

Then the problem is the order in which the items are rendered.  Perhaps your
geometry is not being rendered in the translucent pass.  If you set the
Opacity in the property to 0.995, that will force the geometry to be
rendered in the translucent pass, i.e. after all opaque geometry has already
rendered.  It is the Opacity of the property, rather than the alpha of the
lookup table, that VTK uses to decide whether to use the translucent pass.

What is probably happening in your case is that the geometry is rendered
first, causing a write to the depth buffer.  Then the image is drawn
afterwards, and the depth buffer check causes it not to be written to any
pixels that the geometry rendered to.

 - David


On Fri, Jul 8, 2011 at 12:29 PM, Chris Volpe ARA/SED <cvolpe at ara.com> wrote:

> If depth peeling is something that's off by default, unless you explicitly
> enable it, then I'm not doing it. (In fact, I've never heard of it.) I just
> have 3D geometry with a color lookup table that varies the hue but keeps
> alpha constant at 0.5.
>
>
> -Chris
>
>
> > -----Original Message-----
> > From: David Gobbi [mailto:david.gobbi at gmail.com]
> > Sent: Friday, July 08, 2011 12:43 PM
> > To: Chris Volpe ARA/SED
> > Cc: vtkusers
> > Subject: Re: [vtkusers] transparent 3D over 2D
> >
> > Are you using depth peeling?  Depth peeling disables alpha, it is an
> > alternate strategy to translucent rendering that doesn't use alpha and
> > as far as I understand, it actually requires alpha-blending to turned
> > off in order to work.
> >
> > So I don't think that depth peeling can be used when an underlay is
> > present (or at least, not in VTK).
> >
> >  - David
> >
> >
> > On Fri, Jul 8, 2011 at 10:32 AM, Chris Volpe ARA/SED <cvolpe at ara.com>
> > wrote:
> > > I'm rendering 3D geometry over a 2D image drawn onto the rendering
> > window
> > > using an Actor2D. The 3D geometry  is semi transparent, as can be
> > seen when
> > > some 3D geometry is drawn on top of other 3D geometry. However, the
> > > transparency does not permit seeing the background image through the
> > 3D
> > > geometry. For purposes of the background image, the 3D geometry is
> > > completely opaque. Is this an inherent limitation, or am I doing
> > something
> > > wrong?
> > >
> > >
> > >
> > > Thanks,
> > >
> > >
> > >
> > > Chris
> > >
> > > --
> > > Christopher R. Volpe,
> > > Ph.D.
> > Email:
> > > cvolpe at ara.com
> > >
> > > Senior Scientist, Information Exploitation Systems             Main
> > Desk:
> > > 919-582-3300
> > >
> > > Applied Research Associates,
> > > Inc                                                     Direct: 919-
> > 582-3380
> > >
> > > 8537 Six Forks Rd., Suite
> > > 6000                                                            Fax :
> > > 919-582-3301
> > >
> > > Raleigh, NC 27615                                         Web:
> > > http://www.ara.com/offices/NC.htm
>
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