Quick question on CustomJoints

[Pyritie]

Hi, I'm using MogreNewt (C# wrapper for ogrenewt) and I've been working on a custom joint that allows rotation on all three axes but only allows movement on the X and Z axes.

Here's what I've got so far:

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        public override void SubmitConstraint(float timeStep, int threadIndex) {
            Vector3 globalPos;
            Quaternion globalOrient;
            // get the global position and orientation
            // Not sure if we need the orientation but we need the position at least
            this.m_body0.GetPositionOrientation(out globalPos, out globalOrient);
            // Set the Y of the new position to 0
            // TODO: since we're only constraining it to Y, couldn't this just be 0?
            newGlobalPos = globalPos;
            newGlobalPos.y = 0f;
            // I wonder if there's a way to do this without needing the two rows. Oh well.
            // The first argument is the position we'd like to move, the second argument is where we'd like
            // to move it to, and the third argument says which vector we want to move it along
            addLinearRow(globalPos, newGlobalPos, Vector3.UNIT_Y);
            addLinearRow(globalPos, newGlobalPos, Vector3.NEGATIVE_UNIT_Y);
        }

(I'm pretty sure ogrenewt doesn't have the min/maxLinearLimit stuff so I have to use the rows)

It seems to work right but I'm not sure if what I'm doing is the best way.

[Julio Jerez]

you almost have it, just one listle mistake that can make it unstable, here is the correction

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public override void SubmitConstraint(float timeStep, int threadIndex)
{
   Vector3 globalPos;
   Quaternion globalOrient;
   // get the global position and orientation
   // Not sure if we need the orientation but we need the position at least
   this.m_body0.GetPositionOrientation(out globalPos, out globalOrient);
   // Set the Y of the new position to 0
   // TODO: since we're only constraining it to Y, couldn't this just be 0?

   /   newGlobalPos = globalPos;
   newGlobalPos.y = 0f;
   // I wonder if there's a way to do this without needing the two rows. Oh well.
   // The first argument is the position we'd like to move, the second argument is where we'd like
   // to move it to, and the third argument says which vector we want to move it along
   addLinearRow(globalPos, newGlobalPos, Vector3.UNIT_Y);
               
      // remove this line and it should be fine.
      //addLinearRow(globalPos, newGlobalPos, Vector3.NEGATIVE_UNIT_Y);
}

[Pyritie]

I tried doing that before but then it'd only stop it from moving along negative Y. It could still move along positive Y though.

(By the way, Vector3.UNIT_Y is (0, 1, 0) and Vector3.NEGATIVE_UNIT_Y is (0, -1, 0))

[Julio Jerez]

the direction cancel the accelration not the moment
try the way I tell you, it should work

[Pyritie]

hm, that seems to be working now

It didn't before, weird :0

By the way is there an easy way to add a "maximum velocity" to a body (maybe using this joint since everything in my game will be using it)?

[Julio Jerez]

Lot of things are possible with joints, I am guessing you mean some kind of a velocity depended constraint.

what do you mean maximum velocity? can you explain?

[Pyritie]

Well for example I don't want the player to move faster than a certain velocity.

At the moment I am doing this:

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        private Vector3 velocityVec = new Vector3();
        /// <summary>
        /// Makes a body move! :D
        /// </summary>
        /// <param name="body">The body you want to move</param>
        /// <param name="vec">The vector you want to move it in</param>
        public void ApplyForce(Body body, Vector3 vec) {
            body.AddImpulse(vec, body.Position);

            // Temporary until I find a proper way to do this
            velocityVec = body.Velocity;
            if (velocityVec.x > Kernel.Get<Main>().Player.MaxMoveSpeed)
                velocityVec.x = Kernel.Get<Main>().Player.MaxMoveSpeed;
            if (velocityVec.x < -Kernel.Get<Main>().Player.MaxMoveSpeed)
                velocityVec.x = -Kernel.Get<Main>().Player.MaxMoveSpeed;
            if (velocityVec.z > Kernel.Get<Main>().Player.MaxMoveSpeed)
                velocityVec.z = Kernel.Get<Main>().Player.MaxMoveSpeed;
            if (velocityVec.z < -Kernel.Get<Main>().Player.MaxMoveSpeed)
                velocityVec.z = -Kernel.Get<Main>().Player.MaxMoveSpeed;
            body.Velocity = velocityVec;
        }

But that is kinda crude and only works for the player. If I wanted to do that for every body then I'd have to do this for each body every time its velocity increased somehow (through a collision or whatever).

[JernejL]

Well for example I don't want the player to move faster than a certain velocity.

At the moment I am doing this:

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        private Vector3 velocityVec = new Vector3();
        /// <summary>
        /// Makes a body move! :D
        /// </summary>
        /// <param name="body">The body you want to move</param>
        /// <param name="vec">The vector you want to move it in</param>
        public void ApplyForce(Body body, Vector3 vec) {
            body.AddImpulse(vec, body.Position);

            // Temporary until I find a proper way to do this
            velocityVec = body.Velocity;
            if (velocityVec.x > Kernel.Get<Main>().Player.MaxMoveSpeed)
                velocityVec.x = Kernel.Get<Main>().Player.MaxMoveSpeed;
            if (velocityVec.x < -Kernel.Get<Main>().Player.MaxMoveSpeed)
                velocityVec.x = -Kernel.Get<Main>().Player.MaxMoveSpeed;
            if (velocityVec.z > Kernel.Get<Main>().Player.MaxMoveSpeed)
                velocityVec.z = Kernel.Get<Main>().Player.MaxMoveSpeed;
            if (velocityVec.z < -Kernel.Get<Main>().Player.MaxMoveSpeed)
                velocityVec.z = -Kernel.Get<Main>().Player.MaxMoveSpeed;
            body.Velocity = velocityVec;
        }

But that is kinda crude and only works for the player. If I wanted to do that for every body then I'd have to do this for each body every time its velocity increased somehow (through a collision or whatever).

You could consider a object entity hiearichal call chain in ApplyForce which would do that properly and you'd only have to do it in the main class.

[Julio Jerez]

You can do that in a much simpler and faster way, than using a joint.
In your force call back you can just add a velocity clip fintion like this

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ForceCallback (body)
{
    // apply you gravity and oteh force here
     ...
    ...


  // clip the velocity
  Vector  veloc
  NetwonGetVeloc (body, veloc)
  Float mags =    DotProduct (veloc, veloc)
  If (mags > (MaxVeloc * MaxVeloc)) {
    Vector dir = Normalize (v)
    Veloc = dir .Scale (MaxVeloc)
    NetwonSetVelocity (body, veloc);
  }
}

[Pyritie]

Delfi, I have no idea what you just said D:

You can do that in a much simpler and faster way, than using a joint.
In your force call back you can just add a velocity clip fintion like this

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ForceCallback (body)
{
    // apply you gravity and oteh force here
     ...
    ...


  // clip the velocity
  Vector  veloc
  NetwonGetVeloc (body, veloc)
  Float mags =    DotProduct (veloc, veloc)
  If (mags > (MaxVeloc * MaxVeloc)) {
    Vector dir = Normalize (v)
    Veloc = dir .Scale (MaxVeloc)
    NetwonSetVelocity (body, veloc);
  }
}

Thanks, that seems to work. :D

Here's my code if anyone wants it:

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// This goes wherever
body.ForceCallback += new ForceCallbackHandler(LimitMaximumVelocity);

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static void LimitMaximumVelocity(Body body, float timeStep, int threadIndex) {
            Vector3 veloc = body.Velocity;
            float mags = veloc.DotProduct(veloc);
            if (mags > (Kernel.Get<Main>().Player.MaxMoveSpeed * Kernel.Get<Main>().Player.MaxMoveSpeed)) {
                veloc.Normalise();
                veloc *= Kernel.Get<Main>().Player.MaxMoveSpeed;
                body.Velocity = veloc;
            }
        }

[JernejL]

i have no idea how to express it in C++ sorry, but basically every child class of another would call parent object's submit forces aswell, that way the base gravity capable object would be shared amongst all your entities..

[Pyritie]

Would that be any better than using the force callback?