[vtkusers] Opacity adjustment of actors

[John Biddiscombe]

Try adding a vtkDepthSortPolyData in the pipeline and see if it makes things
look better. It'll slow everything down to a crawl, but if it makes it
better, then your problem is that multiple transparent objects have to be
rendered back to front for correct opengl display.

JB

----- Original Message ----- 
From: "Andrew Usher" <A.C.J.Usher at damtp.cam.ac.uk>
To: <vtkusers at vtk.org>
Sent: Thursday, March 11, 2004 11:20 PM
Subject: [vtkusers] Opacity adjustment of actors


> Hi all,
>
> I'm currently having some strange behaviour with a small application I'm
> developing.
>
> I'm wanting to to have three actors (basically spheres) with textures
> mapped on to them, each one marginally smaller than the last, with each
> successively smaller sphere being inside the larger (although only just!).
> The smallest sphere is the unit sphere and next outer shell is slightly
> larger, and the third slightly larger again. The effect I want to create
> is to zoom in, and as you get closer, increase the transparency of the
> outer shell to reveal the inner sphere, and have this happen again on the
> second to third sphere. This is like the nVidia type earth zoom demo...
>
> Anyway, I've created a vtkCommand class to do this, with adjustments made
> when the mouse is dragged. I set the spheres up (using
> vtkTexturedSphereSource) and assign in the usual way to actors. I then do
> a SetOpacity for the actors but the behaviour is erratic. Does anyone know
> if this could be an issue with having the spheres that are very close
> indeed at three levels? I've done checks on the variables updating the
> opacity of the actors and they report to be working fine, but the new
> opacity isn't updated in the rendered actors. I thought it might be a
> depth buffering issue but I'm unsure as to how to remedy this. I'm on
> VTK-4.2.2 on Redhat 9 BTW.
>
> Any ideas/clues would be most welcome.
>
> Thanks,
>
> Andy Usher
>
> ---------------------------------------------------
> Email: a.c.j.usherATdamtp.cam.ac.uk
> _______________________________________________
> This is the private VTK discussion list.
> Please keep messages on-topic. Check the FAQ at:
<http://public.kitware.com/cgi-bin/vtkfaq>
> Follow this link to subscribe/unsubscribe:
> http://www.vtk.org/mailman/listinfo/vtkusers
>
>