[ODE] how to stopbody enabling by joint

Mark Williams mark at image-engine.com
Fri Oct 26 09:24:11 MST 2007

Krystian Ligenza wrote:
> Mark Williams pisze:
>>> Krystian Ligenza wrote:
>>>> I have look more in mailing list archive, and see that this topic was 
>>>> many times discussed. Main problem is how to set that joint should only 
>>>> affect  one body and other  left  unforced.  Maybe we should think about 
>>>> adding flag for this, by adding dJointSetXXXParam with dParamAffectBoth, 
>>>> dParamAffectFirst, dParamAffectSecond? If joint can link with world, 
>>>> this should not be impossible to do - correct me if I'm wrong?    
>>> Why wouldn't you just create the joint attached to the affected body and 
>>> the world (NULL), then? I do that for collisions in certain cases, for 
>>> example.
>> If you attach a joint to a null-body, then the joint considers that body 
>> to have zero velocity. This is a potential source of error when 
>> colliding against non-simulated yet animated geoms. I think Krystian's 
>> patch has a great deal of value.
> Hope that you are talking about "void dJointSetFixedBodies (dJointID 
> j,const dVector3 p1,const
> dQuaternion q1,const dVector3 p2,const dQuaternion q2)" function that 
> I proposed for adding, becouse I haven't add what I was talking about 
> in this mail (about dJointSetXXXParam ). I have thought, that only 
> thing that is need to be change for all joints is XXXGetInfo2(...), 
> but It seems that all step functions also check if joint is attached 
> to Body and World, so this become too time consume for me to make it 
> good. Also joint can be attached to World - Body, or Body - World, but 
> internally it is always Body-World, so making a param that hide one of 
> Bodies as World would be a tricky part.

Apologies, I realised after I wrote this that you'd not submitted a 
patch for the dJointSetXXXParam stuff. I think it's a good idea, though.


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