[osg-users] Visualization of billboards depending on pre-conditions

[Robert Osfield]

Hi Hartwig,

You can use the occlussion query extension to do the test but the
round trip to the GPU and back be prohibitive for real-time
performance. This is even before you start having to do a second pass
to decide whether to render or not the signs.

Do you really need to do this?  It would be far more complicated and
slower than just rendering the whole sign all the time.

The only way it would be possible to implement this efficiently would
be if you were able to use an OpenGL extension where you could
conditionally render some geometry based on an occlusion query test
all down on the GPU with non CPU intervention.

However, I'm not sure such a GL extension exists, I think I've seen
discussion about such an approach quite a while back but don't recall
if it was just hypothetical or there was some practice implementation
was possible.

Robert.

On 7 January 2017 at 18:39, Hartwig Wiesmann
<hartwig.wiesmann at skywind.eu> wrote:
> Hi,
>
> I would like to show a complete billboard when a certain part of the billboard is visible. Although other parts may be (partially) hidden by other items.
>
> Example: assume that the billboard is a sign consisting out of a foot, pole and the sign itself. Whenever the foot is visible (depth test passes for the whole foot) I would like to show the complete sign. Even if the depth test for the sign fails for certain parts of the sign (but not for the foot).
>
> Does anybody have any ideas how to set up such a test and following visualisation efficiently?
>
> Thank you!
>
> Cheers,
> Hartwig
>
> ------------------
> Read this topic online here:
> http://forum.openscenegraph.org/viewtopic.php?p=69920#69920
>
>
>
>
>
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