[osg-users] Temporarily overriding alpha channel

[Chris Hanson]

Normally I'd do this with some kind of shader and a Uniform to control the
transparency.

If you haven't seen it already, I'd take a look at this set of code we did
for a client a few years ago:

http://alphapixel.com/project/osg-transparency-toolkit/

It was made for large complex CAD scenes where z-sorting is not always an
option. It has a couple of non-sorted transparency approximations with
various side-effects, plus an Order Independent Transparency implementation
you can easily slap into a scene.


I'm not totally sure what you mean by transparency "channel". Channel
usually refers to an image-based transparency/alpha channel, which isn't
usually necessary in order to make a whole subgraph transparent. You'd just
need to set some blend state and such on a parent node and then remove it
when you didn't want it.

Maybe explain more clearly what you think you need and what difficulty you
are imagining it will have?


On Fri, Feb 15, 2019 at 5:41 PM Claudio Benghi <claudio.benghi at gmail.com>
wrote:

> Hi,
>
> Is there a way to override the transparency channel of a sub tree in the
> scene?
>
> My application shows buildings and their components and I want to give the
> user a sort of x-ray vision in some circumstances to help locate items
> behind walls.
>
> I know that ideally this would require to z-sort all the elements in the
> view, but I'm not much concerned with the correct sorting at the moment.
>
> These models are sometimes *very* large, so something that uses an
> override value that I can then cheaply remove would be ideal.
>
> Any ideas?
>
> Thanks,
> Claudio
>
> ------------------
> Read this topic online here:
> http://forum.openscenegraph.org/viewtopic.php?p=75632#75632
>
>
>
>
>
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>


-- 
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