Events

LSL scripts are event driven. The script does nothing until something happens: a touch, a message, a timer, a collision. Then the matching event handler in the current state runs to completion.

Events wait in a queue while a handler runs. Keep handlers short; long work blocks every other event in the script.

There is no runtime subscription to events: a state receives the events it has handlers for. Think of each state as a set of subscriptions; changing state is how a script subscribes and unsubscribes.

Concepts

States
- Every script starts in the default state, and each state has its own handlers
- Changing state fires state_exit and then state_entry, and removes listeners and sensors from the old state
- To stop receiving an event, change to a state without that handler, or remove its source with llListenRemove, llSensorRemove or llSetTimerEvent(0.0)
- Resetting, running state and memory of scripts are covered under Scripts
Timers: each script has one timer, firing the timer event. Timers, sleeping and clocks are covered under Time
Changes to the object: inventory, links, owner, region, teleports, shape and more
- Test the flags with the bitwise AND operator (&)
Detection
- Touch, collision, sensor and damage events can report several detections at once
- The event’s number parameter says how many; llDetected* functions such as llDetectedKey read each one by index, and only inside that event
Sensors scan a cone around the object for avatars or objects, once or repeatedly
- The nearest results arrive in sensor, or no_sensor when nothing is found

Functions and events

`event`	`state_entry()`
`event`	`state_exit()`
`event`	`on_rez(integer start_param)`
`event`	`changed(integer changes)`
`void`	`llSensor(string name, key id, integer type, float radius, float arc)`
`event`	`sensor(integer num_detected)`
`event`	`no_sensor()`
`key`	`llDetectedKey(integer number)`

Event Order

Which events are called for different actions, such as attaching, rezzing, resetting or changing state, and in which order.

Events by feature

Most events belong to a feature. Start from the event index, or from the feature you are working on: input, communications, physics.

Scripting Details

`event`	`state_entry()` Triggered immediately whenever a new state is entered (including at script start). It is always the first event handled.
`event`	`state_exit()` Triggered when the state command is used to transition out of the current state. Handled before entering the new state's state_entry.
`event`	`on_rez(integer start_param)` Triggered when the object is rezzed into the world (by a script or user). Passes start_param from the rezzing call (or 0 if rezzed from inventory). Also triggers on attachments during login or when attached from inventory.
`event`	`changed(integer changes)` Triggered when various properties of the object change. The parameter changes is a bitfield of CHANGED_* flags.
`void`	`llSensor(string name, key id, integer type, float radius, float arc)` Performs a single scan from the prim's forward vector for name and id of type within radius meters and arc radians. Results trigger a sensor or no_sensor event. Passing empty filters (blank name, 0 type, or NULL_KEY id) disables that filter.
`void`	`llSensorRepeat(string name, key id, integer type, float radius, float arc, float rate)` Sets up a repeating periodic scan every rate seconds for name and id of type within radius meters and arc radians of the forward vector. Results trigger sensor or no_sensor events.
`void`	`llSensorRemove()` Removes the periodic sensor previously configured by llSensorRepeat.
`event`	`sensor(integer num_detected)` Triggered when objects matching constraints of llSensor or llSensorRepeat are successfully detected. Passes num_detected, representing the number of detected targets.
`event`	`no_sensor()` Triggered when active sensors (from llSensor or llSensorRepeat) complete a scan without finding any matching targets.

Additional

Time — timers, delays and clocks
- llSetTimerEvent — 0.0 stops further timer events
- llSleep — the script is inactive during this time
- llMinEventDelay — minimum delay between events being handled
- llGetTime, llResetTime, llGetAndResetTime — elapsed script time
- llGetUnixTime, llGetTimestamp, llGetDate, llGetWallclock, llGetGMTclock — real-world clocks
Scripts — resetting and controlling scripts
- llResetScript, llResetOtherScript — reset this or another script
- llSetScriptState, llGetScriptState — stop, start and check other scripts in the prim
- llGetScriptName — the script’s own name
changed — the changes bitfield (all flags)
- CHANGED_INVENTORY — prim inventory changed by someone with modify rights
- CHANGED_LINK — number of prims or seated avatars changed
- CHANGED_OWNER — the object changed owners
- CHANGED_REGION — the object changed regions
- CHANGED_TELEPORT — the avatar this object is attached to teleported
Detected functions — llDetectedKey, llDetectedName, llDetectedOwner, llDetectedGroup, llDetectedPos, llDetectedRot, llDetectedVel, llDetectedLinkNumber (touches and collisions), llDetectedGrab (touches only)
- llDetectedType — bitfield of types (DetectType)
- AGENT — an avatar
- ACTIVE — physical objects and agents
- PASSIVE — non-physical objects
- SCRIPTED — has at least one active script
Common event sources
- touch_start, collision_start, control — input and physics
- listen, link_message, http_request — communications
- dataserver — requested data returned to the script
- run_time_permissions — an agent granted or denied permissions
Script health (see Scripts)
- llGetFreeMemory, llGetUsedMemory — free and used script memory
- llScriptProfiler — PROFILE_SCRIPT_MEMORY tracks peak memory while active
- llGetSimStats — region statistics such as SIM_STAT_SCRIPT_MS (script time per frame) and SIM_STAT_SCRIPT_EPS (script events per second)
- llGetRegionFPS, llGetRegionTimeDilation — region performance
- llGetEnergy — remaining physics energy of the object
- llScriptDanger — whether a position is over public or sandbox land, or land that restricts building or outside scripts

Constant groups

Constant groups ChangeType 13 DetectType 7 ScriptProfileMode 2 SimulatorStat 27

See also Page default Page state SL Wiki LSL StatePlanned Guide: switching event handlers with states