dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Sun, Aug 27, 2006 at 11:00:00PM +0200, Ola Skavhaug wrote:
> Anders Logg skrev den 27/08-2006 følgende:
> > On Sun, Aug 27, 2006 at 09:39:34PM +0200, Ola Skavhaug wrote:
> > > Ola Skavhaug skrev den 25/08-2006 følgende:
> > > > Anders Logg skrev den 25/08-2006 følgende:
> > > > > On Fri, Aug 25, 2006 at 12:10:39PM +0200, Garth N. Wells wrote:
> > > > > > Does PyCC visualise without writing data to a file? This is what I would
> > > > > > like to be able to do. Does PyCC use the DOLFIN mesh library?
> > > > > 
> > > > > I think it writes VTK files.
> > > > 
> > > > PyCC can visualize without writing to file, if the user wishes. We utilize the
> > > > vtkVoidArray class for sending the contents of Numeric arrays directly to the
> > > > graphics card.  Additionally, plotter can write the frames to file as either
> > > > vtk files or png graphics.
> > > >  
> > > > > Yes, PyCC uses the DOLFIN mesh library, but I think the plotter.py script
> > > > > assumes a PyCC wrapper of the DOLFIN mesh. Probably, the extra wrapper layer
> > > > > can be removed when the new DOLFIN mesh is in place with proper Python
> > > > > bindinds.
> > > > 
> > > > Actually, the plotter does not depend on the DOLFIN mesh at all. We have a
> > > > seperate class MeshLister, that can be built from a DOLFIN mesh, that provides
> > > > the data needed in plotter to do runtime visualization in VTK.
> > > > 
> > > > Please, go ahead and use the code in DOLFIN if you want to. We can give you a
> > > > GPLed version of the file.
> > > 
> > > We can change the PyCC plotter license to open source. Can you live with LGPL?
> > 
> > Yes, in particular since I can change the license to GPL. :-)
>  
> I really didn't know that. That basically makes LGPL useless, as I see it.

I agree. I hadn't realized until I looked more closely at the license.

This is of course intentional, to make it easy to change from LGPL to
GPL but not the opposite.

> > Anyone is free to distribute an LGPL-licensed library under the
> > GPL. See section 3 of the LGPL:
> > 
> >     http://www.gnu.org/licenses/lgpl.html
> > 
> > Using GPL or LGPL is an interesting discussion, but I see four main
> > reasons for going with the GPL instead of the LGPL:
> > 
> > 1. All the rest of the DOLFIN code is GPL and it's practical to have
> > the same license for all the code.
> 
> That's a point.
>  
> > 2. Using the LGPL is not safe; anyone can modify and relicense
> > LGPL-covered code under the GPL (like we may do with plotter.py) which
> > would prevent the modifications from being propagated back to the
> > original code. If I make changes under the GPL to plotter.py, you
> > wouldn't be able to benefit from these changes and so a main purpose
> > of open-sourcing plotter.py (getting benefit from user's
> > modifications) would be lost.
> 
>  
> > 3. GPL better promotes free software than the LGPL.
> 
> Let's discuss this issue (again) some time :)

Yes, I'm sure the discussion will continue. :-)

Also, take a look at http://www.gnu.org/licenses/why-not-lgpl.html

> > 4. I can't think of any example (for DOLFIN) where use of the GPL
> > would prevent something desirable that the LGPL would allow, which
> > would outweigh 1-3. But I may be missing something?
> 
> I don't know. I'm not attacking the GPL licence of DOLFIN. Personally, I like
> software that is both free and tolerant (to other licences). Anyway, I'll go
> through the vtkplotter and resolve any dependencies to other PyCC stuff, and
> then fork off a GPL version. 
> 
> Ola

Very nice, thanks!

/Anders