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Project osgPhysics started!

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Sukender
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PostPosted: Wed Jan 14, 2009 2:30 pm    Post subject:
Project osgPhysics started!
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Hi all,

Integration of physics simulation into OSG has been done many times, but OSG still don't have a common layer to plug physics engines in. The project osgPhysics is born from this idea and will be that layer, as discussed before on osg-users mailing list.

OsgPhysics started a few weeks ago, and is still in a planning/pre-alpha state. However, we clearly have the intention to integrate osgPhysics into core OSG, by providing an extensible layer that would accept any physics engine, by the way of plugins. This is why efforts should be concentrated on it, rather than on specific solutions.

We will mainly support the PAL engine ( http://www.adrianboeing.com/pal/ ), since PAL is only an abstraction layer for some popular engines (PhysX, Bullet, ODE, Newton, Tokamak, TrueAxis and more). This way, you may use your favorite engine without having much to do... We also may contribute to the PAL project so that PAL fits our goals.
Native support of engines would still be possible as osgPhysics is "engine agnostic".

Project is (for now) located on SourceForge.net ( http://sourceforge.net/projects/osgphysics ), and already includes and example. Be aware that only PAL engine is supported for now. So if you want to use ODE (for instance), you'll have to build ODE, PAL, and osgPhysics.

Current authors are Wang Rui and Sukender.
Feel free to join and/or discuss the project (please use "[osgPhysics]" tag)! We're waiting for your ideas and comments.

Cheers!

Wang Rui and Sukender, osgPhysics admins


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Sukender
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PostPosted: Wed Jan 14, 2009 2:43 pm    Post subject:
Project osgPhysics started!
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Hi Robert, hi all,

I got a question! Robert and I discussed the fact that the future "osgAudio" may have a specific update traversal.
1. Do you think it could be wise to do a similar "physics update traversal" for osgPhysics?
2. If so, is there a way to code things in OSG so that osgPhysics could benefit from it WITHOUT disturbing existing OSG apps?
3. And finally, is there be someone to code it, or could you send your thought/ideas?

Thank you!

Sukender
PVLE - Lightweight cross-platform game engine - http://pvle.sourceforge.net/


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art (Art Tevs)
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Joined: 20 Dec 2008
Posts: 414
Location: Saarbrücken, Germany

PostPosted: Wed Jan 14, 2009 2:59 pm    Post subject:
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Hi Sukender,

Gratulations to the newly started project!

I had created a subforum (osgPhysics) on our forum. I've also connected the [osgPhysics] tag with this forum. Hence we have a direct place where to post or where to read the related questions Wink

Best regards,
art
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Sukender
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PostPosted: Wed Jan 14, 2009 3:23 pm    Post subject:
Project osgPhysics started!
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Hi Art,

I forgot to ask you about the tag on the forum, and you did it! Marvelous! :)

Sukender
PVLE - Lightweight cross-platform game engine - http://pvle.sourceforge.net/


Le Wed, 14 Jan 2009 15:59:08 +0100, Art Tevs <> a écrit:

Quote:
Hi Sukender,

Gratulations to the newly started project!

I had created a subforum (osgPhysics) on our forum. I've also connected the [osgPhysics] tag with this forum. Hence we have a direct place where to post or where to read the related questions ;)

Best regards,
art

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Robert Osfield
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PostPosted: Wed Jan 14, 2009 3:40 pm    Post subject:
Project osgPhysics started!
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Hi Sukender,

On Wed, Jan 14, 2009 at 2:42 PM, Sukender <> wrote:
Quote:
I got a question! Robert and I discussed the fact that the future "osgAudio" may have a specific update traversal.
1. Do you think it could be wise to do a similar "physics update traversal" for osgPhysics?

It might, or might not be. I really can't provide any guidance
without sitting down with code in front of me that is implementing a
particular feature.

Quote:
2. If so, is there a way to code things in OSG so that osgPhysics could benefit from it WITHOUT disturbing existing OSG apps?

You can always fire off custom traversals from the existing traversals.

Quote:
3. And finally, is there be someone to code it, or could you send your thought/ideas?

Not sure what you mean here.

Robert.


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Sukender
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PostPosted: Wed Jan 14, 2009 3:46 pm    Post subject:
Project osgPhysics started!
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Hi Robert,

Quote:
On Wed, Jan 14, 2009 at 2:42 PM, Sukender <> wrote:
Quote:
I got a question! Robert and I discussed the fact that the future "osgAudio" may have a specific update traversal.
1. Do you think it could be wise to do a similar "physics update traversal" for osgPhysics?

It might, or might not be. I really can't provide any guidance
without sitting down with code in front of me that is implementing a
particular feature.

Well, the problem is that physics don't run at the same rate as display. For instance, we should run a "physics update traversal" at 100Hz, and the "normal" update traversal the fastest possible (well, limited by the VSYNC).


Quote:
Quote:
2. If so, is there a way to code things in OSG so that osgPhysics could benefit from it WITHOUT disturbing existing OSG apps?

You can always fire off custom traversals from the existing traversals.

Hum... do we need to modify the viewer source? I guess so...


Quote:
Quote:
3. And finally, is there be someone to code it, or could you send your thought/ideas?

Not sure what you mean here.

Well you answered at the previous question :)


Sukender
PVLE - Lightweight cross-platform game engine - http://pvle.sourceforge.net/


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Paul Martz
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PostPosted: Wed Jan 14, 2009 5:01 pm    Post subject:
Project osgPhysics started!
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Quote:
Well, the problem is that physics don't run at the same rate as
display. For instance, we should run a "physics update traversal"
at 100Hz, and the "normal" update traversal the fastest possible
(well, limited by the VSYNC).

Then the physics update would run in a separate thread, and you'd need some
mechanism to "pull" the physics state into OSG during the update traversal.
I guess I don't understand why this "pull" couldn't be done in the existing
update traversal.

Quote:
Quote:
You can always fire off custom traversals from the existing traversals.

Hum... do we need to modify the viewer source? I guess so...

I think what Robert is talking about is something like launching a physics
simulation step from a root node update callback (for example). This doesn't
require modifying osgViewer. But I don't think this would satisfies your
requirement to run the physics simulation at a different rate from the
display.

Paul Martz
Skew Matrix Software LLC
http://www.skew-matrix.com
+1 303 859 9466



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LEgregius (David Guthrie)
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Joined: 06 Jan 2009
Posts: 26

PostPosted: Wed Jan 14, 2009 8:10 pm    Post subject:
Project osgPhysics started!
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I'm using PAL for a physics integration with delta3d. I'm still confused
about why people want to integrate things like physics and audio into a
scene graph, but that aside, I am adding features and such to PAL since
I have commit access.

We should all work together implementing features in PAL so we don't
duplicate effort.

I'm going to be working on adding support for collision masks, then
I'm going to look at doing a character model interface.



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Robert Osfield
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PostPosted: Wed Jan 14, 2009 8:44 pm    Post subject:
Project osgPhysics started!
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Hi Paul, Sukender et al,

On Wed, Jan 14, 2009 at 5:01 PM, Paul Martz <> wrote:
Quote:
Then the physics update would run in a separate thread, and you'd need some
mechanism to "pull" the physics state into OSG during the update traversal.
I guess I don't understand why this "pull" couldn't be done in the existing
update traversal.

This is an important point - how to handle the concurrency,
effectively we'd need to have parts of the scene graph cloned by the
rendering scene graph and the physics scene graph, the rendering scene
graph pulling values from the physics scene graph. The physics scene
graph may well be identical, but have a thread just working on
different elements that the rendering thread doesn't modify - such as
a cached matrices or meshes.

Robert.


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Sukender
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PostPosted: Wed Jan 14, 2009 9:00 pm    Post subject:
Project osgPhysics started!
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Hi Paul,

Thanks for the answer... and thanks for improving osgPhysics by the way of discussion.

Quote:
Quote:
Well, the problem is that physics don't run at the same rate as
display.

Then the physics update would run in a separate thread, and you'd need some
mechanism to "pull" the physics state into OSG during the update traversal.
I guess I don't understand why this "pull" couldn't be done in the existing
update traversal.

Well, multithreading *is* an issue, but we need to address the problem.
I guess the order of steps would be:
- When it is time to update the physics, run the "physics update traversal" (say "PUT") in a physics thread
- PUT
- PUT
- ...
- When the times come to update the display, lock the physics thread so that no PUT runs
- Run the "display update traversal" ("DUT") in a display thread. During this, copy physics positions/orientations to transforms.
- Unlock the physics.
- PUT (physics thread), cull and draw (display thread)
- and so on.

Am I right? I'm not sure about threads because here the PUT cant run when DUT runs, so the interest is limited, even if cull and draw steps would be in parallel of a PUT. Maybe there could be improvements. Any idea?


Quote:
Quote:
Quote:
You can always fire off custom traversals from the existing traversals.

Hum... do we need to modify the viewer source? I guess so...

I think what Robert is talking about is something like launching a physics
simulation step from a root node update callback (for example). This doesn't
require modifying osgViewer. But I don't think this would satisfies your
requirement to run the physics simulation at a different rate from the
display.

Well, is it possible to run "n times PUT", and then one time the standard frame (update/cull/draw)? If so, there should be no problem.
For now, physcs objects are updated "manually", by calling something like "for each object { object->update(); }" because all objects are known by a single class (the "World"). The PUT could simply be that kind of loop (instead of a full traversal)... what is the best design, according to you?

Sukender
PVLE - Lightweight cross-platform game engine - http://pvle.sourceforge.net/


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Sukender
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PostPosted: Wed Jan 14, 2009 9:07 pm    Post subject:
Project osgPhysics started!
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Hi David,

Thanks for the info. And yes, you're right about implementing features in PAL.

About the integration of audio and physics, we aim at giving users an easier access to features often coupled with scene graphs. Doesn't it make sense for you? Or maybe we're not talking about the same thing!? I belive that providing a layer that facilitates the use of a physics engine would give users an additional reason to use OSG for any simulation.

Sukender
PVLE - Lightweight cross-platform game engine - http://pvle.sourceforge.net/


Quote:
I'm using PAL for a physics integration with delta3d. I'm still confused
about why people want to integrate things like physics and audio into a
scene graph, but that aside, I am adding features and such to PAL since
I have commit access.

We should all work together implementing features in PAL so we don't
duplicate effort.

I'm going to be working on adding support for collision masks, then
I'm going to look at doing a character model interface.





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LEgregius (David Guthrie)
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Joined: 06 Jan 2009
Posts: 26

PostPosted: Wed Jan 14, 2009 9:27 pm    Post subject:
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I guess I understand why people do it, but I would rather that OSG kept the limited scope of being a scene graph, that is with the features just of doing 3d rendering. I think a more limited scope makes it more useful as a drop in component of a game engine.

physics and audio, while they are necessary in a game or simulation engine, they are not rendered, and I don't think they belong in a scene graph. In delta3d, we have, and are more and more trying to separate things such as drawing, physics, and audio from simulated objects (actors) so that actors can be composed of these features via componentization and messaging. We would eventually even like delta3d to have the ability to use different renderers.

As technologies like raytracing become more prevalent, the scene graph may have change a fair bit, but that shouldn't affect the audio and physics systems.

Originally we had wanted to work with Robert more closely to make delta3d have game engine features, and osg have the rendering features, but things didn't evolve that way.

Either way, this is not a discussion for the osgPhysics list. I'm making dtPhysics, which appears to have nearly exactly the same goals as you have except that we intend to integrate with delta3d its component system.

I email back and forth with Adrian Boeing a fair bit, and I have commit access to PAL, as I said before, so we would discuss the features and direction of PAL, as we see it. Perhaps PAL needs a mailing list, or maybe we need to do something more like a telecon to discuss things. I don't know where in the world you are. I'm on the east coast of the US. Adrian is, I think, in Australia. So, I'm not sure how practical that is.
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hannes_b@gmx.at
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PostPosted: Wed Jan 14, 2009 9:52 pm    Post subject:
Project osgPhysics started!
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Sukender wrote:
Quote:
Hi David,

Thanks for the info. And yes, you're right about implementing
features in PAL.

About the integration of audio and physics, we aim at giving users an
easier access to features often coupled with scene graphs. Doesn't it
make sense for you? Or maybe we're not talking about the same thing!?
I belive that providing a layer that facilitates the use of a physics
engine would give users an additional reason to use OSG for any
simulation.

when you talk about simulation, you do not mean http://caelinux.com and such with finite elements, non-linear thermo-mechanics, coupled fluid-structure dynamics, seismic / non-linear explicit dynamics, contacts, visco-plasticity, fluid dynamics, heat exchange, convection heat transfer and radiation, electro-magnetcis and such. if i understand pal right than it is a game physics layer and not a simulation physics layer.

nothing bad about it, but i think it needs to be mentioned.

would be great if osg would be used more also in the simulation field.

best regards


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Sukender
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PostPosted: Wed Jan 14, 2009 10:00 pm    Post subject:
Project osgPhysics started!
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Hi David,

Well, what we intend to do is simply provide a "plug" so that you can do what you want. Morover, the osgPhysics' aim is to drive nodes in the graph by the way of physics. We don't plan to make physic objects to be "cullable", or things like that. Changeing the renderer (like raytracing) would not affect things handled by osgPhysics.
I hope this is a bit clearer! :)

About Adrian, I also discussed a few points with him, and I may contribute to PAL too. And yes, he's in Australia... Wang Rui (osgPhysics, osgNV) is in China, and I'm in France... well it may be difficult to be all online for a chat, but we still can work :)

Sukender
PVLE - Lightweight cross-platform game engine - http://pvle.sourceforge.net/


Quote:
I guess I understand why people do it, but I would rather that OSG kept the limited scope of being a scene graph, that is with the features just of doing 3d rendering. I think a more limited scope makes it more useful as a drop in component of a game engine.

physics and audio, while they are necessary in a game or simulation engine, they are not rendered, and I don't think they belong in a scene graph. In delta3d, we have, and are more and more trying to separate things such as drawing, physics, and audio from simulated objects (actors) so that actors can be composed of these features via componentization and messaging. We would eventually even like delta3d to have the ability to use different renderers.

As technologies like raytracing become more prevalent, the scene graph may have change a fair bit, but that shouldn't affect the audio and physics systems.

Originally we had wanted to work with Robert more closely to make delta3d have game engine features, and osg have the rendering features, but things didn't evolve that way.

Either way, this is not a discussion for the osgPhysics list. I'm making dtPhysics, which appears to have nearly exactly the same goals as you have except that we intend to integrate with delta3d its component system.

I email back and forth with Adrian Boeing a fair bit, and I have commit access to PAL, as I said before, so we would discuss the features and direction of PAL, as we see it. Perhaps PAL needs a mailing list, or maybe we need to do something more like a telecon to discuss things. I don't know where in the world you are. I'm on the east coast of the US. Adrian is, I think, in Australia. So, I'm not sure how practical that is.



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Sukender
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PostPosted: Wed Jan 14, 2009 10:05 pm    Post subject:
Project osgPhysics started!
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Hi Hannes(?)

PAL is an abstraction layer for real-time simulation, such as games. However, there is nothing against adding support for complex physics to PAL or osgPhysics. This is true that it is not our first intention for osgPhysics but the project is a layer to "whatever you need". So maybe you'll see (ona day) an OpenFOAM or Code_Saturne support... this is possible.

Sukender
PVLE - Lightweight cross-platform game engine - http://pvle.sourceforge.net/


Le Wed, 14 Jan 2009 22:52:28 +0100, <> a écrit:

Quote:
Sukender wrote:
Quote:
Hi David,

Thanks for the info. And yes, you're right about implementing
features in PAL.

About the integration of audio and physics, we aim at giving users an
easier access to features often coupled with scene graphs. Doesn't it
make sense for you? Or maybe we're not talking about the same thing!?
I belive that providing a layer that facilitates the use of a physics
engine would give users an additional reason to use OSG for any
simulation.

when you talk about simulation, you do not mean http://caelinux.com and such with finite elements, non-linear thermo-mechanics, coupled fluid-structure dynamics, seismic / non-linear explicit dynamics, contacts, visco-plasticity, fluid dynamics, heat exchange, convection heat transfer and radiation, electro-magnetcis and such. if i understand pal right than it is a game physics layer and not a simulation physics layer.

nothing bad about it, but i think it needs to be mentioned.

would be great if osg would be used more also in the simulation field.

best regards




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