How to be a good llListener?

I have several illustrative posters in a couple of my properties that I want to be able to hide when they're not needed. I wrote a script (my very first, yaaay!) that listens for commands and shows/hides accordingly. I know, a million people have done it before (or at least a couple hundred thousand) but I wanted to learn.

Anyway, I've heard that listener scripts can be a burden on the system, and I want to make sure I'm being as efficient and unobtrusive as possible. Can anyone offer tips to make my li'l show/hide dealy be a good Second Citizen?

Right now, my script handles listening like this: I've got the following command in the state_entry block: llListen(69, "", id, ""

I had tried using "poster" as the fourth parameter so that I could filter off of that and have two-word commands, like "poster show" and "poster hide" but that didn't seem to work.

Should I be doing anything else, like removing the listen on a given object state, or re-instating the listen on rez or anything? (Hey, at least I knew not to listen on channel 0, but that's the extent of my eliteness.)

Thanks for your advice...

EDIT: P.S. What the heck does that third parameter mean, and what does "id" do? My script works, but I don't know if/how that parameter is affecting it. I don't define "id" anywhere in my script.

llListen(123 <channel it listens on>, "" <name of the object speaking... useful for inter-object comms>, id <the id of the person to listen to, like, owner only would be llGetOwner()>, "beep" <listens only for certain "beep"... "beeper" and "bee" fail>;

llListen(123, "", llGetOwner(), ""; //Listens for anything on channel 123 by the owner of the object containing the script... can be filtered out later.

How I tend to filter is

listen(integer channel, string name, key id, string message)
{
     if(llToLower(message) == "beep")
     {
           llPlaySound("beep", 1.0);
     }
}

If using multiple channels...

listen(integer channel, string name, key id, string message)
{
     if(llToLower(message) == "beep" && channel == 123)
     {
           llPlaySound("beep", 1.0);
     }
}

Not sure if i understand the description right, but if this is some sort of help drawings attached to items, maybe it'd be better to allow user toggle them either by directly clicking on the item, or through menu invoked with such click? This way there's no need for any long-term listen filters, and it might be even more user-friendly this way...

The message filter is unforunately pretty unhelpful because noone knows what channel other items the owner is going to have, or what other objects are present locally if using a global listener.

I dont know how much of a overhead the message filter adds to a listener either. Assuming that a listener using the filter is less intensive than doing your own filter with substrings and the like, then a good way may be to use something like the following:

integer visible = TRUE;
integer handle;
integer chan = 69;

default
{
   state_entry()
   {
      handle = llListen(chan,"",id,"poster");
   }

  listen(integer channel, string name, key id, string msg)
  {
      if (msg == "poster");
      {
         llOwnerSay("listening...");
         llListenRemove(handle);
         if (visible) handle = llListen(chan,"",id,"hide");
         else handle = llListen(chan,"",id,"show");
      }
      if (msg == "hide");
      {
         llOwnerSay("hiding....");
         hidePoster();    //  hide poster function here
         visible = FALSE;
         llListenRemove(handle);
         llListen(chan,"",id,"poster");
      }
      if (msg == "show");
      {
         llOwnerSay("showing....");
         showPoster();    //  show poster function here
         visible = TRUE;
         llListenRemove(handle);
         llListen(chan,"",id,"poster");
      }
   }
}

Without testing its hard to say whether this would actually reduce the overhead on such a small script. On larger scripts though, removing listen handlers when they are not needed would be a good.

In fact having reread llListenRemove there may be a better way...

integer visible = TRUE;
integer channel = 69;

default
{
   state_entry()
   {
      llListen(chan,"",id,"poster");
   }

   listen(integer channel, string name, key id, string msg)
   {
      llOwnerSay("listening....");
      if (visible) state hide;
      else state show;
   }
}

state hide
{
   state_entry()
   {
       llListen(chan,"",id,"hide");
   }

   listen(integer channel, string name, key id, string msg)
   {
      llOwnerSay("hiding....");
      visible = FALSE;
      hidePoster();
     state default;
   }
}

state show
{
   state_entry()
   {
       llListen(chan,"",id,"show");
   }

   listen(integer channel, string name, key id, string msg)
   {
      llOwnerSay("showing....");
      visible = TRUE;
      showPoster();
     state default;
   }
}

Since a change in state removes any listeners in that state this does away with the need to manaually remove the listener.

In both cases you trigger the script to change to a state waiting for the next command, aslong as the initial value for visible is correct and nothing goes wrong this should trigger the function to hide or show the poster without having a listener waiting for absolutely any input, really it should have a timer in the show and hide state or show and hide if statements so that it resets automatically if the second command isnt given after a certain time.

As I said in this case I doubt it would make much difference, perhaps in a larger script with more commands :/

Could some uber LSL scripter shed some light on it

So, basically, the posters are illustrations of how to use various objects in the room. The objects themselves are no-mod (and weren't created by me), so the posters must be external.

And to Teffler, I'm going to have to re-read your suggestion a couple more times to understand what you're demonstrating... but I have a feeling I'm going to have a couple questions. Thanks!

Hehe

Sorry, I suck at the explaining bit

     integer visible=TRUE;
   listenSet(string m){
   	llListenRemove(listener);
   	listener=llListen(69,"",llGetOwner(),m);
   }
   default{
   	state_entry(){listenSet("poster hide");}
   	listen(integer c,string n,key d,string m){
   		if(visible){visible=FALSE;listenSet("poster show");hidePoster();}
   		else{visible=TRUE;listenSet("poster hide");showPoster();}
   	}
   } 

Oh god... lmao

I had to read it a couple times to understand how it worked, but I do believe this is a thing of beauty. Thank you.

Could someone send me the script that uses the "voting machine" that is around different places in sL?

thanks

When I want a low-lag listener (like in my vendors), I hook into touch_start. When the item is touched, it starts a 30 second timeout timer, and starts a listener. In the listen event handler, it resets the 30 second timeout timer. If the timer goes off, it turns off the listener and goes back to sleep.

- Jon

The following link from the WIKI will give you the option to touch the poster to activate the listen, and use a chat command to shut the listen off.

http://secondlife.com/badgeo/wakka.php?wakka=llListenControl

Alternately... you can use a touch start with a timer event to shut the listen off within 30 seconds (or whatever you need). This will give you the opportunity to use the listen feature while reducing system burden by disabling the listen when you don't need it.

Of course... if you need multiple posters to enable and disable at the same time without touching all of them before giving the command... this won't work for you.

Depending on whether or not you need to move the posters around, and their relative distance from one another... you could in fact use link messages to tell all of the posters to start listening when you touch 1 of them.

Just some ideas.

The touch idea is a great one, although I can see the issue if you can't link 'em. The key to reducing server usage is to filter them at the llListen call as much as possible. This is because the server only does anything with chat if it hits the criteria of the listen (i.e. on the right channel, is said by the right av or object, etc.) If you leave your listen wide open (as in the second example below) then the server will process the if statement every time something is said on channel 69.

Thus

integer channel=69;
string name="My Avatarname";
key id="mykey"; //not entirely necessary if you're already using your name
string message = "";

default
{
   state_entry()
   {
      llListen(channel,name,key,message);
   }
   listen(integer ch, string nm, key avkey, string msg) 
   {
      //insert whatever you want to do here
   }
}

works much more efficiently than

default
{
   state_entry()
   {
      llListen(69,"",NULL_KEY,"");
   }
   listen(integer ch, string nm, key avkey, string msg) 
   {
      if(nm=="myname" & msg = "command")
       {
           //whatever you want it to do here
       }
   }
}

In all actuality though, I've found that unless you have a large number of listens, or a large number of people talking nearby, the actual server effect can be relatively minimal. The biggest thing to remember though is that unless you have a really good reason for user operability (i.e. in a vehicle where the user may be a little busy to type a specific channel), you should almost never place a listen on channel 0, and if you must be on 0, never use it without filtering for at least an avatar name.