Rezzing objects facing another object?

I'm trying to get an object (say, ObjectA) to sense another object (ObjectB), and rez an object (Object C) between them. This much was simple. However, where I'm stumped is trying to set the math so that ObjectC has its largest face (it's a flat square) facing ObjectB.

That's convoluted. For anyone who has seen, say, the Sion shield, that shield does what I'm trying to do, basically, by rezzing convex circles between an oncoming object and the av it's headed towards. I'm sorta trying to replicate that effect for different purposes.

Again, it's the rotational math that's bugging me on this, and not the pos vector. Can anyone get me started in the right direction?

Here's something that might help:

// AXIS_* constants, represent the unit vector 1 meter along the specified axis.
vector AXIS_UP = <0,0,1>;
vector AXIS_LEFT = <0,1,0>;
vector AXIS_FWD = <1,0,0>;

// getRotToPointAxisAt()
// Gets the rotation to point the specified axis at the specified position.
// @param axis The axis to point. Easiest to just use an AXIS_* constant.
// @param target The target, in region-local coordinates, to point the axis at.
// @return The rotation necessary to point axis at target.
rotation getRotToPointAxisAt(vector axis, vector target)
{
    return llGetRot() * llRotBetween(axis * llGetRot(), target - llGetPos());
}

If you're making a shield, you've probably already picked off the object coming towards you with a sensor, so you should know WHAT the object is that is coming towards you.

Have you tried llRotLookAt??

http://secondlife.com/badgeo/wakka.php?wakka=llRotLookAt

Just a thought:

If you used a big, hollowed sphere with whatever cuts/dimples you like to make it look nice you could skip the positioning of it.

I'm not actually making a shield, LOL. I just meant that the Sion Shield does this same thing - rezzing an object that is rotated to face the target.

llRotLookAt is great, but it acts on the object after it is rezzed and sensing already all by itself. I want the objec to be rezzed - non-physical - and already facing the sensed object.

Is Object A allowed to face Object B?

If so, use the llRotLookAt on Object A, then you'll be able to get the params using something like llGetRot or llGetPrimitiveParams to use in your llRezObject for rezzing object C.

If you cant rotate object A, how about an inviso prim that you can just use as a reference?

I think what Luc is looking for is the maths to calculate the rotation from the two position vectors. I shouldn't think that's too difficult, but my 3D maths is shabby at best.

Chris' code should work.

ZERO_ROTATION * llRotBetween( ( llRot2Up( ZERO_ROTATION ) ) * ZERO_ROTATION, llDetectedPos() - llGetPos() )

in the rotation value of the llRezObject call should work. I'm not in world to test atm though.

Good point. Just saw the llGetRot()s and skipped over it.

I'll give Chris' code a shot and report back.

Of course, my report will probably be flavoured by the fact that I am simply not that bright.

Thanks, Chris!

Okay... this is what my script-kiddie-like implementation of this script has wrought...

The plates do consistently rez at an angle to the target that seems to be based on the target's location in relation to the rezzing object's. But that rotation is not facing the target, but rather at an odd angle to the target.

Any suggestions about how I might adjust this rotation, perhaps to account for the object's natural shape? I'm not sure how to find the offset between what the computation thinks the object's natural axis are, and what the actual prim's axis are.

For figuring out the orientation for odd-looking shapes, I just rez one, orient it so it "looks right", and then read off the Euler orientation from the object tab. Then a quick translation to Radians and conversion to rotation can be most conveniently done in the script...