llRotLookAt

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/LSL

RotLookAt

llRotLookAt

Summary

Function: llRotLookAt( rotation target_direction, float strength, float damping );

0.0	Forced Delay
10.0	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.

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

See Also

Functions

•	llLookAt
•	llStopLookAt
•	llSetPhysicsMaterial
•	llSetKeyframedMotion

Deep Notes

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