Hello Alexander,
On 05/22/2012 07:52 AM, Alexander Lang wrote:
> what is the policy regarding vertex and geometry shaders in a cluster
> environment?
> With vertex and geometry shaders, OpenSG loses some control over the
> geometry as the user is able to transform the geometry arbitrarily beyond
> the standard model-view-projection transformation.
>
> Obviously, frustum culling and ray-cast picking via IntersectAction will
> not work as expected since OpenSG works on the untransformed bounding
> volume.
yes, the automatically calculated bounding volumes can not accommodate
for transformations that only happen in shaders. I've used manually set
bounding boxes for animated characters in the past and made them large
enough to contain all motions of the character.
> A solution for picking would be to use Color Picking with an ID-Buffer as
> demonstrated by the idbuffer.cpp example.
>
> Are there any other areas within OpenSG that exhibit problems with
> geometry that is heavily transformed by vertex/geometry shaders?
> Especially in a cluster environment like a CAVE, will you have to expect
> display artefacts?
Without doing anything: yes, because as you've mentioned frustum culling
will operate on incorrect bounding volume information and that is going
to cause problems at the edges between screens in a CAVE. On the plus
side, if you can provide (conservatively) correct bounding volumes even
the load balancing algorithms (i.e. sort first, sort last) should work
since IIRC they only use bounding volume information to decide which
cluster node renders which geometry.
So if the amount of geometry that is transformed by shaders is small you
may even be able to simply set its bounding volume to infinite.
Cheers,
Carsten
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