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b2MouseJoint Issue

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roadkillguy

Post subject: b2MouseJoint Issue

Posted: Tue Jan 17, 2012 2:25 pm

Joined: Wed Sep 07, 2011 12:38 pm
Posts: 8

Hello,

I'm not sure what I'm doing wrong here, but every time I create a mouse joint like so:

Code:

                b2MouseJointDef mouseJointDef;
                mouseJointDef.maxForce = 100;
                mouseJointDef.bodyA = body;
                mouseJointDef.bodyB = m_groundBody;
                mouseJointDef.target = b2Vec2(10, 10);

                m_mouseJoint = (b2MouseJoint *)m_world->CreateJoint(&mouseJointDef);

I get this at the next call to Step()

Code:

/build/src/Box2D_v2.2.1/Box2D/Dynamics/Joints/b2MouseJoint.cpp:125: virtual void b2MouseJoint::InitVelocityConstraints(const b2SolverData&): Assertion `d + h * k > 1.19209289550781250000e-7F' failed.
Aborted

d + h * k is extremely vague, and I was hoping you guys could keep me from pulling my hair out. Can anyone decode this for me? I'm clueless as to what's wrong.

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irresistible force

Post subject: Re: b2MouseJoint Issue

Posted: Tue Jan 17, 2012 9:04 pm

Joined: Tue Jun 24, 2008 8:25 pm
Posts: 1517
Location: Tokyo

Try making body A the ground.

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roadkillguy

Post subject: Re: b2MouseJoint Issue

Posted: Tue Jan 17, 2012 11:09 pm

Joined: Wed Sep 07, 2011 12:38 pm
Posts: 8

Interesting... That seemed to have worked. What is the proper way to initialize a ground body? Now that the mouse joint is applied properly the body flies around the page.

EDIT: My problem was that I wasn't using the target property on the b2MouseJointDef class. Problem solved. Thanks!

Last edited by roadkillguy on Wed Jan 18, 2012 12:19 am, edited 1 time in total.

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irresistible force

Post subject: Re: b2MouseJoint Issue

Posted: Tue Jan 17, 2012 11:53 pm

Joined: Tue Jun 24, 2008 8:25 pm
Posts: 1517
Location: Tokyo

The default values for b2BodyDef are set as a static body positioned at 0,0 so it could be as simple as:

Code:

b2Body* groundBody = world->CreateBody( &b2BodyDef() );

... although some compilers will not like that

Typically you would do:

Code:

b2BodyDef bodyDef;
b2Body* groundBody = world->CreateBody( &bodyDef );

Are you moving the anchor point somehow? If not, it should settle down pretty quickly even when the initial movement is large.

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roadkillguy

Post subject: Re: b2MouseJoint Issue

Posted: Wed Jan 18, 2012 12:21 am

Joined: Wed Sep 07, 2011 12:38 pm
Posts: 8

Whoops, didn't see your post.

I wasn't using the target property of b2MouseJointDef, and for whatever reason that caused the body to fly to the bottom right whenever I called SetTarget().

Thanks for the help

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