lookAt() modification

Troubleshooting graphics
1

Hi all, and merry christmas.



I've a problem in one of my spare time projects that has been bugging me for quite a while. I'm playing with an IK implementation and my bones simply won't do what i want.

My plan is to modify the Quaternion.lookAt() method:


public void lookAt(Vector3f direction, Vector3f up ) {
        tmpZaxis.set( direction ).normalizeLocal();
        tmpXaxis.set( up ).crossLocal( direction ).normalizeLocal();
        tmpYaxis.set( direction ).crossLocal( tmpXaxis ).normalizeLocal();
        fromAxes( tmpXaxis, tmpYaxis, tmpZaxis );
    }



I use a rig from blender, which has Y going along the length of the bone. I think i've now tried every combination of axis changing/flipping, but the bones never point where they're supposed to, and i must now admit that my grasp of quaternions is rather weak. It seems it shouldn't be that hard for someone with better understanding of math.
To summarize what i want help with:
I'd like to have the bone point towards "direction", but along the Y axis, rather than Z.

Thanks!
2

Thanks ttrocha.



I had noticed your modification, but thought it was a separate issue that i needed to look at after this was fixed. I'll apply it now and see if it solves my problem.



Cheers,

Rickard

3

Ok, i've modified my lookAt() to use ttrocha's addition as well, and there seems to be better consistency in the bones now. I still don't get the results i'm after though, and i would appreciate if someone could fill me in on some quaternion stuff.

I've thought a bit more about what it is i want to achieve, and if i use a standard Quaternion.lookAt(), i think i need to rotate it 90 degrees around the X-axis, and 90 degrees around the Z-axis.



And to clear up my original explanation; i need the Y-axis to be "forward", along the "dir".



Alternatively, i think it would solve my problems if there was a way in blender to change how bones are aligned, so that Z is going along the length of the bone, rather than Y. Does anyone know if that is possible?



Thanks,

Rickard