LlListen

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Summary

Function: integer llListen( integer channel, string name, key id, string msg );

Sets a callback for msg on channel from name and id.
Returns an integer that can be used to deactivate or remove the listen.

• integer channel any valid integer (-2147483648 through 2147483647).
• string name filter for specific prim or avatar name
• key id filter for specific prim/avatar UUID.
• string msg filter for specific chat message

If msg, name or id are blank they are not used to filter incoming messages. If id is an invalid key or a null key, it is considered blank.

Specification

For the listen event to be triggered it must first match the criteria set forth by the filters; only when all the criteria have been met is a listen event generated. First the message must have been transmitted on channel channel. If name is set then the speaker's name must match name exactly. If id is a valid, non-null key then the speaker's key must be equivalent. If msg is set then the spoken message must match msg exactly.

Channel Constant Description
DEBUG_CHANNEL 0x7FFFFFFF Chat channel reserved for script debugging and error messages, broadcasts to all nearby users.
PUBLIC_CHANNEL 0x0 Chat channel that broadcasts to all nearby users. This channel is sometimes referred to as: open chat, local chat and public chat.

Caveats

  • On state change or script reset all listens are removed automatically.
    • A state change can be used as a shortcut to releasing listens.
  • Only 65 listens can simultaneously be open in any single script.
    • If this number is exceeded Script run-time error and Too Many Listens errors occur.
  • Chat on negative channel numbers cannot be generated by the client except with dialog boxes.
    • This makes it ideal for object2object communications.
    • This may just be an artificial limitation placed on the client and not the underlying protocol.
  • Once a listen is registered it's filters cannot be updated, if the listen is register to llGetOwner, the listen will remain registered to the old owner upon owner change.
    • Owner change can be detected with the changed event.
    • To work around this the old listen will need to be closed and a new one opened for the new owner.
  • A prim cannot hear/listen to chat it generates. It can, however, hear a linked prim.
All Issues ~ Search JIRA for related Bugs

Examples

Trivial example to listen to any chat from the object owner and respond once. To reduce lag and avoid spamming surrounding users, it is vastly preferable to listen on channels other than 0 and to trigger the listen event by chatting on an alternative channel such as '/5 hello'. <lsl>// says beep to owner the first time owner says something in main chat; integer listen_handle;

default {

   state_entry()
   {   // Registers the listen to the owner of the object at the moment of the call.
       // This does not automatically update when the owner changes.
       // Change 0 to another positive number to listen for '/5 hello' style of chat.
       listen_handle = llListen(0, "", llGetOwner(), "");
   }
   listen( integer channel, string name, key id, string message )
   {
       llOwnerSay("beep");
       // Stop listening until script is reset
       llListenRemove(listen_handle);
   }
   on_rez(integer param)
   {   // Triggered when the object is rezed, like after the object had been sold from a vendor
       llResetScript();//By resetting the script on rez it forces the listen to re-register.
   }
   changed(integer mask)
   {   // Triggered when the object containing this script changes owner.
       if(mask & CHANGED_OWNER)
       {
           llResetScript();
       }
   }
}</lsl>

Notes

  • Avoid channel 0 and set name or id where possible to avoid Lag. llListen(0,"","","") can be extremely laggy as it listens to all chat from everyone in chat range and so it should be avoided at all cost.
  • In November 2007, Kelly Linden offered this explanation to help scripters plan listeners more efficiently:
  1. Chat that is said gets added to a history.
  2. A script that is running and has a listen event will ask the history for a chat message during its slice of run time.
  3. When the script asks the history for a chat message the checks are done in this order:
    • channel
    • self chat (prims can't hear themselves)
    • distance/RegionSay
    • key
    • name
    • message
  4. If a message is found then a listen event is added to the event queue.
The key/name/message checks only happen at all if those are specified of course.
So, the most efficient way is llRegionSay on a rarely used channel.

See Also

Events

•  listen

Functions

•  llListenRemove Removes a listen
•  llListenControl Enables/Disables a listen
•  llWhisper Sends chat limited to 10 meters
•  llSay Sends chat limited to 20 meters
•  llShout Sends chat limited to 100 meters
•  llRegionSay Sends chat limited current sim

Deep Notes

All Issues

~ Search JIRA for related Issues
   Listeners in child prims get positioned at root prim position first, then switch to child prim position after re-rez (resulting in wrong listener / whisper radius)

Signature

function integer llListen( integer channel, string name, key id, string msg );