[ODE] New Joints format

[Bill Sellers]

Hi All,

Often the best way of achieving a particular effect (best as in  
stable and quick) is to create a new joint. Whilst this isn't  
particularly difficult in the current ODE (although some extra  
documentation would help) once you've written your custom joint it is  
a real pain to keep on top of code revisions because you need to keep  
private copies of 5 different files and repatch the new ones. It  
seems to me that we could probably come up with a format that allows  
just a single custom_joints.cpp and custom_joints.h file - preferably  
that can be defined at ./configure time. Certainly all the changes to  
joint.cpp, joint.h, ode.cpp would be fine. The changes in objects.h  
would also be fine since anyone using a custom joint can probably  
cope with being careful not to use the non-public interface to their  
new joint. The only real problem is common.h since you need to add  
extra joint types and the easiest way I can think of to fix that is  
to include a few dJointTypeUser1, dJointTypeUser2, dJointTypeUser3  
definitions at the end of the enum. There isn't really any overhead  
associated with doing that - I'd add 100 extra definitions to make  
sure there are enough for anyone (and the enum will still fit into a  
char if that is what your compiler wants to do).

Cheers
Bill