Rotation combination

Ok, I am fairly befuddled. I have the following:

// from the Wiki
rotation getRotToPointAxisAt(vector axis, vector target) {
    return llGetRot() * llRotBetween(axis * llGetRot(), target - llGetPos()); }

// adapted from forum code by Pedro Pendragon
float getRoll(rotation now) {
    vector v = llRot2Fwd(llGetRot());
    float heading = llAtan2(v.y, v.x);

    float run = llSqrt(v.x * v.x + v.y * v.y);
    float pitch = -llAtan2(v.z, run);

    rotation y = llEuler2Rot(<0, pitch, 0>);
    rotation z = llEuler2Rot(<0, 0, heading>);
    rotation x = now / z / y;
    vector tmp = llRot2Euler(x);
    float roll=tmp.x;

    return roll; }

Now when I rotate my object as follows:

llSetRot(getRotToPointAxisAt(<1,0,0>, target));
llSetRot(llEuler2Rot(<-getRoll(llGetRot()), 0, 0>) * llGetRot());

I get perfect alignment, but two visible motions. Not a problem! Just combine
the rots, right?

rotation first = getRotToPointAxisAt(<1,0,0>, target));
llSetRot(llEuler2Rot(<-getRoll(first), 0, 0>) * first);

but apparently this is the wrong way to combine those two operations. Help!

- C

Probably in your getRoll() function you want to do this instead:

vector v = llRot2Fwd(now);

Looks like you're using llGetRot() there, which will give you the rotation previous to 'first' (because it hasn't happened yet)

D'oh! Transformations piled on top of transformations. You're dead right. Thanks.

How I wish LSL was a FP language.

- C