# Difference between revisions of "LlRotLookAt"

 LSL Portal
Function: llRotLookAt( rotation target_direction, float strength, float damping );
 127 Function ID 0 Forced Delay 10 Energy

Causes an object to smoothly rotate to target_direction with strength resistance at damping force.

Maintains rotation target_direction until stopped with llStopLookAt.

 • rotation target_direction • float strength • float damping – seconds to critically damp in

To change the position in the same manner, use llMoveToTarget. For physical objects a range between .2 and 1 is good for both parameters.

## Caveats

• In Non-Physical objects this function operates effectively the same as llSetLocalRot.
• damping seems to be capped at 1.0; greater values are reduced to 1.0 (Tested 21 October 2010 on server version 10.10.18.212360)
• The minimum value for strength seems to be 0.0445 for the function to have any effect.
All Issues ~ Search JIRA for related Bugs

## Examples

#### Point the prim's positive y axis (<0.0, 1.0, 0.0>) towards a position on the sim

```//-- where vPosTarget is the global position of the object you want to "look" at
llRotLookAt( llRotBetween( <0.0,1.0,0.0>, llVecNorm( vPosTarget - llGetPos() ) ), 1.0, 0.4 ); // Point +Y axis towards vPosTarget```
• vPosTarget - llGetPos() converts the global coordinates of the objects, to a local distance and direction from the object pointing
• Per llRotBetween article:
• llRotBetween returns a scaled rotation, unless both inputs are equal magnitude (e.g. unit vector).
• The use of llVecNorm reduces the magnitude to 1 (so that both are equal magnitude), preventing errors.

#### Constraining the Rotation to One Axis

```      vector detected = llDetectedPos( 0 );
vector pos = llGetPos();
llRotLookAt( llRotBetween( <0.0, 1.0, 0.0>, llVecNorm( <detected.x, detected.y, pos.z> - pos ) ), 1.0, 0.4 );```

## Useful Snippets

• If you want a (mostly) smooth constant (rather than damped) rate of motion in a non-physical object try this
```//-- Rotates Object to vRotTarget at vFltRate (in radians per second
//-- vFltRate < ~0.00000003rad/sec, (~0.00002deg/sec) will result in errors (and is just too slow anyway)
//-- vFltRate >= (PI * 5.0)rad/sec, (900deg/sec) will result in a single snap move to vRotTarget
uSteppedRotLookAt( rotation vRotTarget, float vFltRate ){
if ((integer)(vFltRate = (llAngleBetween( llGetLocalRot(), vRotTarget ) / (vFltRate / 5.0)))){
rotation vRotStep = llAxisAngle2Rot( llRot2Axis( vRotTarget / llGetLocalRot() ),
(1.0 / vFltRate) * llRot2Angle( vRotTarget / llGetLocalRot() ) );
vFltRate = (integer)vFltRate;
do{
llSetLocalRot( vRotStep * llGetLocalRot() );
}while (--vFltRate);
}
llSetLocalRot( vRotTarget );
} //-- for fixed time on any rotation try llSetKeyframedMotion```

### Functions

 • llLookAt • llStopLookAt • llSetPhysicsMaterial • llSetKeyframedMotion

## Deep Notes

#### All Issues

 SVC-1903 llRotLookAt & llLookAt do not update the object's bounding box

#### Signature

```function void llRotLookAt( rotation target_direction, float strength, float damping );
```