LlApplyImpulse - Second Life Wiki

LlApplyImpulse

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Summary

Function: llApplyImpulse( vector momentum, integer local );

Applies impulse to object

• vector momentum
• integer local boolean, if TRUE momentum is treated as a local directional vector, if FALSE momentum is treated as a region directional vector

Instantaneous impulse. llSetForce has continuous push. "Instantaneous" seems to mean a one second impulse, as an application of a force (in newtons) equal to the object's mass (in kg) for one second will accelerate it to a velocity of 1 (in meters per second), which appears to be what happens with this function.

Caveats

  • Only works in physics-enabled objects.
  • Sets an initial momentum on the object applied to the center of Mass . Momentum is the mass*velocity needed to get an initial movement of velocity if the object is not affected by other forces ( as the gravity )
  • The magnitude of momentum may be scaled back by the object's available energy. For heavy objects , the cap of momentum will be momentum = 20000 . ( and not 20 as told previously ). For fast objects , the velocity will be capped to 202 meters/second ( and so the momentum will reflect this cap )
All Issues ~ Search JIRA for related Bugs

Examples

//  Rez an object, and drop this script in it.
//  This will launch it at the owner.
 
default
{
    state_entry()
    {
        key ownerKey = llGetOwner();
        vector ownerPosition = llList2Vector(llGetObjectDetails(ownerKey, [OBJECT_POS]), 0);
 
//  if the owner is not in the sim, stop fooling around
        if (llGetAgentSize(ownerKey) == ZERO_VECTOR)
            return;
 
//  else
        llSetStatus(STATUS_PHYSICS, TRUE);
 
        vector objectPosition = llGetPos();
        vector direction = llVecNorm(ownerPosition - objectPosition);
 
        llApplyImpulse(direction * 100, 0);
    }
}

Make yourself a beer can, drop this script into it, and have some target practice.

vector gHome;
integer gHit;
 
default
{
    collision_start(integer num)
    {
        if (!gHit)
        {
            llSetTimerEvent(15.0);
            gHome = llGetPos();
            gHit = TRUE;
        }
        llSetStatus(STATUS_PHYSICS, TRUE);
        llTriggerSound("b90ed62a-2737-b911-bb53-6b9228bbc933",1.0);
        llApplyImpulse(llGetMass()*<0,0,5.0>,TRUE);
        llApplyRotationalImpulse(llGetMass()*<llFrand(1.0),llFrand(1.0),llFrand(1.0)>,TRUE);
        llResetTime();
    }
 
    land_collision(vector where)
    {
        if (llGetTime() < 0.5)
        {
            llResetTime();
            llApplyImpulse(llGetMass()*<0,0,llFrand(1.0)>,TRUE);
            llApplyRotationalImpulse(llGetMass()*<llFrand(1.0),llFrand(1.0),llFrand(1.0)>,TRUE);
        }
    }
 
    timer()
    {
        llSetStatus(STATUS_PHYSICS,FALSE);
        gHit = FALSE;
        llSetRegionPos(gHome);  // Send the can home, even if more than 10m away
        llSetRot(ZERO_ROTATION);
        llSetTimerEvent(0.0);
    }
}
/*
Uselesse script , just to demo that 
* the parameter is a momentum not a force
* the initial velocity * mass = momentum when there are no other forces ( collisions, gravity )
* the momentum is not capped to 20
* momentum may be capped nevertheless because velocity is capped around 200 meters/second ; in this case it will be capped to 200m/s * mass
 
*/
 integer tid;
 vector initPos;
 vector Impulse;
default
{
    state_entry()
    {
        llSetPhysicsMaterial(GRAVITY_MULTIPLIER,0,0,0,0);
        llSetStatus(STATUS_PHANTOM, TRUE);      
        llSetStatus(STATUS_PHYSICS, TRUE);
 
 
    }
 
    touch_end(integer n)
    {
        tid=llTarget(initPos=llGetPos(),30);
        llSetStatus(STATUS_PHYSICS, TRUE);
        Impulse = llGetMass()*<0,0,25>;
         llOwnerSay(llList2Json(JSON_ARRAY, [ "Setup a Momentum=", Impulse  ]));
        llApplyImpulse( Impulse , FALSE);
    }
    moving_start()
    {
        llOwnerSay(llList2Json(JSON_ARRAY, [ "Velocity= ", llGetVel(), "Force=",llGetMass()*llGetAccel(), "Momentum=", llGetVel()*llGetMass()]));
    } 
    not_at_target()
    {
        llSetTimerEvent(0.0);
        llTargetRemove(tid);
        llSetStatus(STATUS_PHYSICS, FALSE);
        llSetRegionPos(initPos);
 
    } 
 
}
 
/* Example of results
["Setup a Momentum=","<0.000000, 0.000000, 183.181381>"]
[10:19] Object: ["Velocity=","<0.000000, 0.000000, 25.000002>","Force=","<0.000000, 0.000000, -0.171902>","Momentum=","<0.000000, 0.000000, 183.181396>"]
 
And for an heavy object, the cap is 20000
["Setup a Momentum=","<0.000000, 0.000000, 28244.332031>"]
[11:01] Object: ["Velocity=","<0.000000, 0.000000, 17.702671>","Force=","<0.000000, 0.000000, -28.363781>","Momentum=","<0.000000, 0.000000, 20000.005859>
*/

See Also

Functions

•  llApplyRotationalImpulse
•  llSetForce Set continuous force

Deep Notes

Unpredictability

Taken from Simulator User Group/Transcripts/2012.10.05

[16:24] Andrew Linden: the llApplyImpulse() is even more unpredictable
[16:24] Andrew Linden: because it uses the legacy script "energy budget"
[16:25] Andrew Linden: which will attenuate the results if the scripted object doesn't have enough "energy" to execute the impulse that it wants
[16:25] Andrew Linden: also, that llApplyImpulse() has great griefing potential
[16:25] Andrew Linden: so we hobbled it a long time ago with a very high energy consumption rate

All Issues

~ Search JIRA for related Issues
   llApplyImpulse now works only in the root prim.
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