[osg-users] unrendered objects creating performance problems?

Robert Osfield robert.osfield at gmail.com
Wed Sep 10 00:56:50 PDT 2008


Hi Joseanibal,

By default the OSG does not cull on the near/far planes, and near/far
clipping is done down on the GPU only affect the fill rate performance
of your application.   You can enable culling on the near/far planes,
but you have to be careful about setting your near/far planes so that
encompass your scene - as the OSG by default computes the near/far
planes it'll hide the inappropriately set near/far planes so by
toggling these features on you might suddenly find parts of foreground
or distance disappearing.

To switch off the compute of near far use the Camera methods
(inherited from osg::CullSettings) :

  viewer.getCamera()->setComputeNearFarMode(osg::CullSettings::DO_NOT_COMPUTE_NEAR_FAR)

To enable the culling against the far plane use methods inherited from
osg::CullSettings again:

  int cullingMode = viewer.getCamera()->getCullingMode() |
osg::CullSettings::FAR_PLANE_CULLING;
  viewer.getCamera()->setCullingMode(cullingMode);

All of this doesn't really address the performance issue too much.
You don't mention the nature of your database at all i.e. how you
built it, what scene graph components it uses, or what hardware, or
OS, or OSG version you are using, all this info is essential for
others to know enough to really guide you in the right direction.

Robert.


On Wed, Sep 10, 2008 at 1:08 AM, Joseanibal Colon Ramos
<jcolon at email.arc.nasa.gov> wrote:
> Hi all,
>
> I was hoping someone has an idea about why I am encountering the following
> problem: I have a big terrain and on certain viewing angles it contains a
> huge amount of triangles to draw and puts a big strain on OSG's
> performance. I tried playing around with near/far clipping planes to
> improve performance, by cutting out a lot of the rendering, to the point
> only a very small fraction (and even none at all) of the terrain is seen
> through my camera. OSG's framerate, however, behaves just as if I was
> looking at the whole thing and drawing all the triangles.
>
> At certain angles, the framerate increases (where small number of
> triangles would normally be - even thought I don't see anything),
>
> and at other angles, it decreases (the same angles at which the viewer
> normally tries to draw a large number of triangles - even though I can't
> see anything). What is going on here?!? help!
>
> -J
>
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