Limiting rotation of Transform to one axis at a time.

Question

I have a situation where I want to force a transform returned from a picking tool to only rotate around or translate along a single axis. To do this, I'm using the transformChanged() function shown below. It works fine for the translation changes, but has problems for the rotation case. If the rotations are about one axis only it's ok, but when rotations are combined (30 degrees on X, then 60 degrees on Y) say, the object flips around in strange ways.
I understand that my approach to the rotation limit was too simplistic, but none of the other approaches I've tried has worked either. I'm very new to Java3D programming and have run out of ideas, can anyone else suggest something to try?
// Callback from Picking tools.
public void transformChanged(int type, TransformGroup tg)
    if((selObj != null) && (tg != null))
        // Get the current Transform3D
        Transform3D current = new Transform3D();
        tg.getTransform(current);
        // Get the current transform vector
        Quat4f currQuat = new Quat4f();
        Vector3f currVect = new Vector3f();
        current.get(currQuat, currVect);
        double currScale = current.getScale();
        System.out.println("transformChanged - scale = "+current.getScale());
        // Set global current variables
        curPosition = currVect;
        curQuat4f = currQuat;
        // Only allow movement on the chosen axis
        if(moveX)
            if(type == PickingCallback.TRANSLATE)
                currVect.setY(oldPosition.getY());
                currVect.setZ(oldPosition.getZ());
            else if(type == PickingCallback.ROTATE)
                currQuat.setY(oldQuat4f.getY());
                currQuat.setZ(oldQuat4f.getZ());
        else if(moveY)
            if(type == PickingCallback.TRANSLATE)
                currVect.setX(oldPosition.getX());
                currVect.setZ(oldPosition.getZ());
            else if(type == PickingCallback.ROTATE)
                currQuat.setX(oldQuat4f.getX());
                currQuat.setZ(oldQuat4f.getZ());
        else if(moveZ)
            if(type == PickingCallback.TRANSLATE)
                currVect.setX(oldPosition.getX());
                currVect.setY(oldPosition.getY());
            else if(type == PickingCallback.ROTATE)
                currQuat.setX(oldQuat4f.getX());
                currQuat.setY(oldQuat4f.getY());
        // Set old global variables.
        oldPosition = currVect;
        oldQuat4f = currQuat;
        // Set the rotation and position back
        // into the transform.
        current.set(currQuat, currVect, (float)currScale);
        // Set the Transform3D back into the TransformGroup
        try
            tg.setTransform(current);
        catch(BadTransformException btex)
            System.out.println(btex);
            System.out.println("current transform = \n"+current);
}Edited by: billphil on Mar 17, 2008 10:56 AM
Edited by: billphil on Mar 17, 2008 11:07 AM
Edited by: billphil on Mar 17, 2008 11:18 AM
Edited by: billphil on Mar 17, 2008 11:21 AM

Answer 1

thanks!
i have tried using a file as a shared resource, and i
can now check whether an instance of my application
is already running. however, i can't make the
currently running application window to be
automatically displayed after the checking. Ar running application could listen on a port so you could tell it to display itself by using TPC/IP. This would require some additinals code in your app, but that shouldn't be a real problem.
If you shared resource is already a port then you could use this port. And if it is a file you could add some additionla information to this file. Like the port number. In this case you could avoid having to use a predefined port (that could be already used by a a completely different app even though it is not very likely) by using an anonymous ServerSocket (by using "new ServerSocker(0)" and "getLocalPort()")