SL/RL Interfaces — An Overview

There are three main interfaces that can bridge the gap between SecondLife and real life:

* e-mail – E-mail is the simplest of Second Life’s external interfaces and the one that can be used without an external server. On the downside, it also has the greatest lag and highest latency. Outbound the Lindens add 20 seconds of script lag to each call, inbound there’s no scripted lag but your messages are subject to normal E-mail delays. E-mail is designed to be slow but reliable, for example, the spec requires that clients retry failed messages and suggests a 30 minute retry interval. I’m sure you’ve seen much delays up even to several days.

* xmlrpc – xmlrpc is the only option that allows an external program to trigger an in-world event, in fact xmlrpc can only be triggered externally triggered though the script can send data out in a reply. Xmlrpc is low lag and low latency, the Lindens add 5 seconds of script lag and only when your script sends a reply. Sending a reply is optional from the standpoint of lsl, but not replying will likely raise an error in your external code. Xmlrpc communication is based on channels which are assigned by Second Life’s servers. Any program using xmlrpc must include a mechanism to get the channel identifier out of SL. The other two SL/RL interfaces are prime candidates though you could ask users to copy and paste. You should also make provisions to open a new channel when the old one idles out, the scripted object rerezzes or changes region, or the channel is closed by a grid reset. This is rare, but something you need to plan for.

* http request – while xmlrpc uses http internally you’re not supposed to think about that. If you wanted to think about it you would use http request. Http request effectively turns Second Life into a web browser. Http has no lag and low latency, the Lindens limit it to 100 requests per 100 seconds, you’ll have to add your own lag if needed to stay within that limit. You can use three of the http methods; GET, POST, and PUT. GET and POST are commonly used in web sites, with a little bit of effort you can interface them to any web framework you’re familiar with, either to retrieve data or send it to a form. You’ll need to format your data and run it through llEscapeURL yourself, but your framework will handle it from there just fine. PUT is a little less common in web applications and may turn up somewhere odd in your framework, but it can be used to send unformatted data very nicely. All http requests are initiated from within Second Life, but they can retrieve up to 2k from your web service. With the low lag you could easily poll to allow an external service to trigger events in SL.

I’ll write more about each of these in later entries or take questions by comment or e-mail.

Weather Wisdom – RL Weather in SL

After we posted the control panel In Kenzo left us a note inviting us to enter into the NMC Connect art show. While Bill and I had defiantely talked about the possibilities of building some sort of art piece using the technology, hopefully a large installation and likely working with a more established artist, we certainly weren’t expecting to do one just a couple weeks later. But, we didn’t want to pass up the opportunity either. So, Bill, Sandhya2 Patel, and I sat down to brainstorm how to run our skills into art. Sandhya2 was a great help since unlike Bill and I she is an incredibly skilled artist. Bill chipped in with the comment that we could do light and temperature easy, so, of course we came up with a plan that required a barometer. Sandhya2 built a wonderful little german weather house, Bill got a barometer, and I wired the whole thing through so that the sensor is entangled with both the actual Weather House and an in world replica of the controller.

Here’s the finished in-world build:

And the finished real world controller:

You can see the build up until the 13th at http://slurl.com/secondlife/NMC%20Campus%205/225/124/20. We’ll probably put it up again somewhere else after the show, but we can’t be sure just where yet. Also, after the show we definitely want to hook up the LEDs that we have in the world build. Hooking up 3 devices to one serial port takes a little doing and we had to cut it out of the RL controller.

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