rotating composite bodies

Game Mechanics
#1

Hi - How do you rotate composite bodies? I have one that is made up of a number of GeomTransforms, and I’m trying to rotate it around its Z-axis at a particular angular velocity, but I’m having no luck.

I’ve tried using the setAngularVel() method on the body and I’ve also tried using AMotors, but the body just doesn’t rotate.

#2

How about applying a torque about the z-axis?

#3

That doesn’t seem to have any effect either.

Here is the code that I’m using. Does it look right?


    this.sideWalls = new Body(world);
    this.sideWalls.setGravityMode(0);

    this.groundGeomB = new GeomBox((float)this.bounds.getWidth(), 10f, 50f);
    this.groundGeomT = new GeomBox((float)this.bounds.getWidth(), 10f, 50f);
    this.groundGeomL = new GeomBox(10f, (float)this.bounds.getHeight(), 50f);
    this.groundGeomR = new GeomBox(10f, (float)this.bounds.getHeight(), 50f);

    this.groundGeomBE = new GeomTransform("t1");
    this.groundGeomTE = new GeomTransform("t2");
    this.groundGeomLE = new GeomTransform("t3");
    this.groundGeomRE = new GeomTransform("t4");

    this.groundGeomBE.setEncapsulatedGeom(this.groundGeomB);
    this.groundGeomTE.setEncapsulatedGeom(this.groundGeomT);
    this.groundGeomLE.setEncapsulatedGeom(this.groundGeomL);
    this.groundGeomRE.setEncapsulatedGeom(this.groundGeomR);

    this.sideWalls.addGeom(this.groundGeomBE);
    this.sideWalls.addGeom(this.groundGeomTE);
    this.sideWalls.addGeom(this.groundGeomLE);
    this.sideWalls.addGeom(this.groundGeomRE);

    this.groundGeomB.setPosition(0f, (float)(-1 * this.bounds.getHeight()/2 - 5), 0f);
    this.groundGeomT.setPosition(0f, (float)(this.bounds.getHeight() + 5), 0f);
    this.groundGeomL.setPosition((float)(-1 * this.bounds.getWidth()/2 - 5), 0f, 0f);
    this.groundGeomR.setPosition((float)(this.bounds.getWidth()/2 + 5), 0f, 0f);

    this.geomIDs.add(this.groundGeomBE.getNativeAddr());
    this.geomIDs.add(this.groundGeomLE.getNativeAddr());
    this.geomIDs.add(this.groundGeomRE.getNativeAddr());
    this.geomIDs.add(this.groundGeomTE.getNativeAddr());

    this.sideWalls.adjustMass(10f);
    this.sideWalls.setPosition((float)(this.bounds.getWidth()/2 + this.bounds.getX()),
                         (float)(this.bounds.getHeight()/2 + this.bounds.getY()),
                         0f);


    space.addBodyGeoms(this.sideWalls);
    this.sideWalls.setAngularVel(50, 0, 0);
    this.sideWalls.addRelTorque(5000,0,5000);
#4

This looks right… The body should rotate regardless of the geoms attached to it. Are you sure that world.step() or world.quickStep() is being called iteratively?

edit:
Is the Body in contact with any other geoms that are keeping it from turning?

#5

It seems to be fixed now. I had to manually set an inertial tensor and center of mass with setMassParameters. I also changed the ordering around a bit. Not sure why this was necessary though.

Thanks for the help though :stuck_out_tongue:

#6

Ah yes. A Body with transformed geoms does not seem to function correctly (at least correctly determine collisions in my experience) unless initial inertial parameters are set.