[osg-users] Displaying cables

[Rémy Deslignes]

Just a stupid question : if the bottleneck is the update of the hose, 
what would you think about using VBOs ?

Laurent Di Cesare a écrit :
> Jean-Sébastien Guay wrote :
>   
>> Hello,
>>
>> For now, we are creating some geometry (quad strips, specifically) to 
>> display the cables, and assigning texture coordinates to that geometry, 
>> on the fly. 
>>   
>>     
> (...)
>   
>> I know the cable display needs to be optimized because if I just set the 
>> cables' nodemasks to 0, the draw times go from 6.6ms to 2.2ms (for the 
>> same view). And there are not *that* many cables... There's a lot of 
>> other geometry in the scene which is still drawn in the 2.2ms time...
>>
>> So I would appreciate some pointers. I would have assumed quad strips 
>> are pretty fast, so perhaps something else is the problem?
>>
>> There's the fact that the geometry is dynamic, which could mean that OSG 
>> is trying to recreate display lists each frame, but I tried 
>> setUseDisplayList(false) on the geometry and the cables just did not 
>> display anymore... Is there something else I need to do in that case?
>>   
>>     
> I have a somewhat similar situation myself. I use capsules to display 
> hoses,
> which aren't textured but just have a color, and use display lists.
> Capsules are just cylinders and half spheres, but these are made of a 
> lot of vertices.
> I ran at something like 1-2 fps(!) when I was redrawing the whole hose 
> everytime the hose changed.
> When no geometry changed, I shot back to around 25 fps.
> I got three times faster when I limited myself to changing only the end 
> of the hose, thus keeping the same capsules rather than replacing them 
> with new ones with the same coordinates, color, etc.
> I then got another factor 3 by making sure I drew as few capsules as I 
> needed.
> In my case too, the capsules are not that many, I have tens of animated 
> characters moving around, plus a scene to render, but the dynamic shapes 
> ate way more than anything else.
> I'm not sure if this helps a lot, but I just did this today, and 
> optimizing the geometry was clearly a big win for me.
> If your app doesn't change all the cables at once, only one part of one 
> cable at a time (a given frame), keeping the geometry should give you a 
> decent boost.
>
> If anyone else has other suggestions, I'm interested to hear them too.
>
> Sincerely,
> Laurent Di Cesare.
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-- 
Remy Deslignes

Ingenieur Developement / Software Engineer 

Tel: +33 (0)1.53.90.11.19

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