Joints

[kyleroche]

Hi, I've been reading through similar posts, but I'm still having issues. I'm trying to pin an arm to a static body. At this point, it's just falling off the screen.

This is where I create the static body (it's been changed a few times due to errors and attempts to fix this issue)

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    body = cpBodyNew(mass, cpMomentForBox(mass, self.contentSize.width, self.contentSize.height));
    
    body->p = location;
    body->data = self;
    //cpSpaceAddBody(space, body);
    
    shape = cpBoxShapeNew(body, self.contentSize.width, self.contentSize.height);
    shape->e = 0; 
    shape->u = 0;
    shape->data = self;
    //shape->group = 1;
    shape->collision_type = 0;
    cpSpaceAddShape(space, shape);
    

I create a non static body, add it to the space and then pin it as such:

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cpConstraint *josephHandPinJoint = cpPinJointNew(joseph.body, josephHand.body, cpv(114, 107), cpv(0, 0));
cpSpaceAddConstraint(_space, joesphHandPivotJoint);

The hand just falls off the screen. Is there a tutorial or example around that I could follow that shows you how to put a static body on the screen that is not affected by touch or gravity then attach some rotating bodies to it (like arms)?

Thanks. Sorry for the very similar question to others you already have posted.

Kyle

[slembcke]

You might want to re-read the section on static and rogue bodies here: http://chipmunk-physics.net/release/Chi ... ougeStatic

What you are creating is a rogue body (because it's not added to the space), and it presumably doesn't have infinite mass. An infinite mass rogue body can effectively function as a static body, but real static bodies as created by cpBodyNewStatic() have a special flag set that allow objects to fall asleep when touching them. If your rogue body doesn't have infinite mass and you aren't manually updating it weird stuff will happen.

[kyleroche]

Hi. Thanks for the quick reply.

Interesting... so, if the body to which i'm pinning the arms will never move, should I just make that a sprite? then ping the arms to the &space->staticBody?

Would that make more sense than what I'm trying to do?

[slembcke]

That would work completely fine yes. It can be convenient to make extra static bodies just for code organizational purposes, but if you can share them that's good too. It would be a little wasteful of memory to make thousands of little shapes, one for each little static shape or joint, but it probably wouldn't affect performance that much.

[kyleroche]

Thanks again! I pinned it to the &space->staticBody. Much smoother now.

Cheers