Possible GPL issue with PhysX

D'raekmus · **Joined:** Sat Nov 29, 2008 2:47 am **Posts:** 35

Well, I'm not sure how feasible it is... but, when replaying my Myst V game, I noticed one of the credits referenced the ODE, the open Dynamics Engine, a physics engine, which is under the LGPL.

Now, the way I see it, we can kill two birds with one stone: if we ask Cyan to consider working on releasing their information regarding the ODE implementation in Plasma (NOT, mind you, releasing Myst V or even more of their engine. Just the libraries and calls to ODE), we might have more feasibility, legally speaking.

In addition, by getting off of PhysX, we would be able to take a far more open approach (If we get some REALLY good devs to work on the ODE library, we might be able to rival the Havok engine in performance!) and modify a greater portion of the code... without having to use a different physics engine.

But, I'm no programmer, so I'm not sure to what extent the ODE is released. Surely more than PhysX, though.

Perhaps this would also increase our own ability to implement cross-platform support, as well as add in a 64-bit client for those running the advanced OSes.

Then again... I saw the latest PhysX have a Linux client... hmm... who knows. Just a rambling thought.

PaladinOfKaos · **Joined:** Thu Aug 03, 2006 10:55 pm **Posts:** 625

ODE from Myst 5 won't cut it for Uru physics, not by a long shot.

I've had good luck with Bullet in PlasmaClient, and I do have plans to port CWE to use Bullet... it's one of many things on my list.

MustardJeep · **Posted:** Wed May 04, 2011 6:09 am

Wow put my foot in it a little bit the early version of GPLv3 I saw a while back wasn't nearly as nasty as the finished product.

Wonder why in creation Cyan picked it.

Deledrius · **Posted:** Wed May 04, 2011 3:12 pm

MustardJeep wrote:

Wonder why in creation Cyan picked it.

I was going to assume it's due to the server provisions of the Affero clause, but it seems they chose not to use that particular version.

PaladinOfKaos · **Joined:** Thu Aug 03, 2006 10:55 pm **Posts:** 625

MustardJeep wrote:

Wow put my foot in it a little bit the early version of GPLv3 I saw a while back wasn't nearly as nasty as the finished product.

Wonder why in creation Cyan picked it.

I assume they picked it becasue it means they'll be the only company that can offer closed-source licenses - a more distributor-friendly OSI license would allow someone else to create a closed product from the code.

The GPL is fine for this, but they need to add the correct linking exceptions.

Keikoku · **Posted:** Fri May 06, 2011 7:22 pm

PaladinOfKaos wrote:

The GPL is fine for this, but they need to add the correct linking exceptions.

A linking exception is enough to allow distribution of binaries made from the existing code, but still leaves a couple of problems:

1. It needs to be made clear that any contributions are made under GPLv3-with-exceptions, not just GPLv3 (or compatible, e.g. GPLv2-or-later). Ideally, before someone is granted commit access, they should provide an explicit licence statement regarding their contributions.

2. We can't use any GPL libraries without first getting exceptions from their authors. And unless the library is developed by a relatively small team of people (or it requires GNU-style copyright assignment), getting such an exception is unlikely.

In the longer term, replacing PhysX with Bullet would eliminate a significant issue. The OpenSSL issue could potentially be worked around by delegating connection management to a plug-in (e.g. invoking ssh or s_client to create the connection).

PaladinOfKaos · **Joined:** Thu Aug 03, 2006 10:55 pm **Posts:** 625

While those are overall ecosystem issues and they do (somewhat) limit the directions the code can go by limiting which libraries we can use, I'm mostly just concerned with making sure distributing client builds is 100% legal.

I am in favor of replacing non-GPL components when possible... but it's not a particularly high priority, as long as they don't interfere with distributing client builds.

ChloeRhodes · **Joined:** Wed Apr 11, 2007 3:29 am **Posts:** 520

PaladinOfKaos wrote:

While those are overall ecosystem issues and they do (somewhat) limit the directions the code can go by limiting which libraries we can use, I'm mostly just concerned with making sure distributing client builds is 100% legal.

I am in favor of replacing non-GPL components when possible... but it's not a particularly high priority, as long as they don't interfere with distributing client builds.

Couldn't we simply, create an install package for the client itself that would copy the required libraries from the physx directory into the Uru directory. So in short, when installing you install the PhysX SDK. Then the you open the install package that we distribute and it simply installs the Uru components onto your system in the appropriate places, and copies the PhysX and any other GPL issue libraries from the previous SDK download into the new Uru directory?

Keikoku · **Posted:** Mon May 16, 2011 2:06 am

ChloeRhodes wrote:

Couldn't we simply, create an install package for the client itself that would copy the required libraries from the physx directory into the Uru directory. So in short, when installing you install the PhysX SDK. Then the you open the install package that we distribute and it simply installs the Uru components onto your system in the appropriate places, and copies the PhysX and any other GPL issue libraries from the previous SDK download into the new Uru directory?

I don't think that this is sufficient. Even if we don't include the PhysX or OpenSSL DLLs in any binary distribution, the executable itself still has to be built using those libraries' header files.

Stucuk · **Joined:** Sun Jun 27, 2010 1:41 am **Posts:** 216

Newton Game Dynamics is under the ZLib License which is compatible with the GPL license.

Newton went Open Source earlier this year. Newton unlike some Physics Engines has been designed to be as accurate/stable as possible(So you don't have ragdolls flying away magically like you do in Half-Life 2 when you put a ragdoll in a doorway and close the door) but at the same time fast(It has 2 solvers, one thats very accurate but slower and one designed for real-time usage such as games).

PaladinOfKaos · **Joined:** Thu Aug 03, 2006 10:55 pm **Posts:** 625

if Newton is GPL-compatible now, I may make the effort to look into it. I'd basically decided to use Bullet already, since I had good luck with it in PlasmaClient. I made the initial decision to use bullet for PC before Newton was open-source, though.

Stucuk · **Joined:** Sun Jun 27, 2010 1:41 am **Posts:** 216

PaladinOfKaos wrote:

if Newton is GPL-compatible now

According to the GNU website the ZLib License (Which Newton uses) is compatible with the GPL License. There is nothing which states its incompatible with GPLv3 (According to the GNU website if they don't state that a particular license is incompatible with a version of GPL then all versions should be compatible).

Mac_Fife · **Posted:** Tue May 17, 2011 5:51 pm

The illustration in the GPL Quick Guide expresslly shows zlib as compatible with both GPLv2 and GPLv3: http://www.gnu.org/licenses/quick-guide-gplv3.html

Possible GPL issue with PhysX

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