Inheriting from cpPivotJoint

[supertommy]

Today I tried to make a joint that inherits from cpPivotJoint, but I ran into a couple of snags. There isn't really any elegant way to supply my own cpJointClass object, and calling the inherited preStep and applyImpulse functions is not possible.

May I propose something like the attached patch? It just exposes a couple of static functions and slightly modifies the interaction between the new and init functions.

It touches only cpPivotJoint, but if you like it, I can make a new patch which does the same to all the joints.

[slembcke]

I was thinking about this too. I think the best way to handle this is to split the "class" definitions out into another header. That way you can copy the struct and replace functions that you want without having to make the joint functions visible. Not quite as elegant as real OO, but it could easily be wrapped by any OO or non OO language.

I'll take a look at your patch after work.

[supertommy]

Yeah, I see what you mean. The joint functions are currently private, my patch makes them public, but we really want them to be protected, to use c++ terms.

One more thing I thought of, by the way. Should we add a destructor function to the cpJointClass? It could be that someone would like to do some cleaning up as their joint dies.

[slembcke]

[supertommy]

This sounds very promising. I'm especially looking forward to the top-down constraints you mentioned. I did actually try to implement top-down friction joints for a racing game some time ago, but it turns out I suck at math and physics .

[supertommy]

[slembcke]

You can declare the struct in the header using an extern and define it in the C code making use of the static functions in scope.

[supertommy]

[slembcke]

[supertommy]