[osg-users] Scaling down a subgraph including frustum clipping: ClipNodes?

Robert Osfield robert.osfield at gmail.com
Tue Sep 2 04:02:46 PDT 2008


Hi Alex,

It sounds like osg::Scissor (wraps glScissor) would be what you need.

Robert.

On Tue, Sep 2, 2008 at 11:25 AM, Alexander Löffler <alexloeffler at gmx.net> wrote:
> Hi all,
>
> I want to scale down a subgraph of my scene (everything below the Transform
> that scales it) to a smaller size inside the view frustum. The tricky part
> is that only those parts that are currently visible in the original
> full-size scene should also be visible in the scaled-down version. This
> means, the clipping that is applied at the clipping planes of the view
> frustum should also be applied to the smaller version. The whole process
> should be done multiple times on a different subgraph each, i.e. the result
> would be my regular view containing several scaled-down scenes, each clipped
> to its own clip planes.
>
> I looked at the osgclip example, which already looks quite promising, so the
> ClipNode is probably what I want. (I didn't really understand why culling is
> disabled in the example, though. Switching it on again didn't change
> anything visibly.)
>
> Are there some kind of limitations to the ClipNode, imposed by the
> underlying glClipPlane? Like a maximum number of clip planes in the entire
> scene, or does the performance drop hugely for each additional clipping
> defined like that?
>
> Thanks a lot for your help,
> Alex.
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