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

[tianzjyh]

Hi, 
    Occlusion query is a better idea, especially for rendering many billboards.


    About the performance, here is a discussion, 
    http://gamedev.stackexchange.com/questions/118651/opengl-occlusion-culling-huge-performance-drop
    which points out that calling all the queries together and waiting for query results asynchronously should minimize the performance loss.
    If you want to implement like that, you should pay more attention to depth test when some billboards overlap each other.





--





Cheers, 
---
TianZJ



At 2017-01-08 18:32:35, "Robert Osfield" <robert.osfield at gmail.com> wrote:
>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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