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Sim Crossings


Melania Namanari
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Are difficult sim crossings just a feature that we have to put up with in SL, or are some makes of vessels better at handling sim crossings than others? Or does your computer capability make any difference? I often see my ship go shooting off acrtoss the map, or sink, or jump backwards, or spin on the spot when crossing sim borders, and it is a few seconds before I can regain some control. Some information on the experiences of others would be useful!

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Rubber banding, falling through pavement, and general lag have been topics of never-ending discussion in SL since Day One.  It's always one of the leading complaints among pilots, sailors, and anyone who handles a vehicle.  Yes, there are some scripting solutions for certain region-crossing issues.  For example, it is common to become unseated as you cross a boundary, so you lose control of a vehicle and pop out of animations. With careful scripting, a vehicle can be designed to recapture those permissions, at least some of the time.  There are definitely some vehicles that are better designed than others.

You can minimize other problems by being more careful as you travel across regions and by carrying as little with you as you can.  Approach borders slowly and at right angles instead of speeding across them nearly parallel to the border. Avoid crossing at region corners. Don't weight your vehicle down with extra scripts and a lot of baggage.  When you cross from one region to another, the servers on both sides have to keep track of where you are, how fast you are moving, and what you have with you. If they can't predict your likely position, you are likely to be in limbo for a while -- possibly long enough that the servers lose track of you entirely.  You disconnect.

No matter what you do and how well-designed your vehicle may be, there's no way to avoid all problems.  Servers have a lot to do other than watching your vehicle. If a region is already full of avatars, has a lot of physical objects in it, and is dealing with new objects being rezzed, the servers can't be expected to treat your vehicle as gracefully as you would like. Travelling into or out of a busy region will always be bumpy.

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With the Firestorm viewer you have a choice about how it handles your region crossing. Unlimited Predictive is one choice. The viewer attempts to predict where you are going as you cross to another region. That prediction can run indefinitely as the viewer is waiting for the server to update it on where you are.

The reason there is a wait is the system packages up all your information, compresses it, passes it to the destination region, which then unpacks it, adjusts position to the latest changes (clicks or keys) and updates the viewer then everything coniutes on.

One big factor is scripts. All the script code and data is packed and sent. The destination server unpacks it, loads the scripts and data then starts them running. Vehicle scripts and all scripts attached to the avatar are transferred.

While all this is happening the viewer is updating the screen based on the last information it had and how you have told it to handle crossings. If you have it set to unlimited predictive, it uses your last server sent direction and velocity to figure out where you 'should' be and how much you may have rotated in the X, Y, And Z axes. If you are using 'limited' predictive the idea is it will stop after it assumes the prediction has grown too large and is likely wrong. FS's idea of that does not seem to include stopping object rotation. The result is the vehicle and you stick on the region boundary and if you were turning or lunging across the waves that motion will continue, giving you the "spin" or sinking look.

Serious sailors and fliers usually have a classic avatar stripped of everything, zero scripts, just for sailing and flying. They also have NO ATTACHMENTS. Only the vehicle is a problem. This gives you the best chance to make a crossing intac. 

The problem comes and goes. Crossings work best, usually, after region restarts, so Tuesday after 12 or an hour or two after the restarts complete. But, you have to watch for regions that did not reconnect well. Having a draw distance of 512 and the mini map open with parcels showing and about 1/2 (1cm) to 1/4 inch in size will show you disconnected regions or empty space in time for you to avoid it... unless you are flying an F-18 at mach 8... than you splat on the region boundary like a bug. I've learned how to make panic turns in my Shergood EC-135 flying at 150kph using the mini-map.

There are discussions about this problem at the Tuesday UG meeting. Bunches of people were ripping on the Lindes from 10/2019 to 2/2020 because ot got bad. Way better now. But, there are days when crossings suck.

There is hope the uplift to the cloud will improve crossings... or we may just have further to fall...

 

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One of the main reasons I have the mini-map up when I'm driving or boating is so I can see when I'm getting close to a region crossing, so that I can slow down and make sure I'm crossing it at a right angle. 

Also, once I start to cross it, if my vehicle starts to go wacky, I take my hands of the keyboard until the vehicle is back on the road where it should be.   For vehicles that drive on roads, for the most part, the vehicle does return to where it should be on the road, and usually I'm sitting fine in it when it does.  

(I do more driving on roads than sailing, so I'm not as familiar with all the ways boats can go wacky).

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5 hours ago, Nalates Urriah said:

FS's idea of that does not seem to include stopping object rotation.

That's my code. Firestorm 6.3.9 should stop rotation at region crossings when it gets much beyond 20°. If you see much more than that, please take a screenshot and let me know. Thanks.

Note this is all in the viewer, and affects only what you see. It has no effect on region crossing failures, or that horrible case where the viewer loses control of the vehicle for several seconds and then gets control back, probably after hitting an obstacle. Some vehicles, including my own bikes, detect that in LSL and freeze in place or warn the user. Several people think this has been happening more lately. It seems to be worse during SL busy periods.

With better vehicles, there's some region crossing assistance in the vehicle's LSL code. Mine do this:

  • On each region crossing, momentarily freeze the vehicle until the avatars catch up. This is about 40ms of delay when things are going well, so you don't see it, and much longer when the sims are in trouble, when you need it.
  • After the region crossing is complete, force the velocity vector to what it was going into the crossing. So you come out moving in the same direction you went in.
  • Off the edge of a region, force a hover height. Region crossings actually trigger when you're 1m off the region, to prevent frantic switching when on the edge, so there's a short distance when you're out of the region but the next sim hasn't picked you up yet. This is when you sink. This trick prevents sinking at region crossings where the surfaces don't extend a little into the next sim.
  • Slow down close to region corners. Way, way down if about to cross two region boundaries.

Everything I do was used in some other vehicle before I did it, but many builders kept these techniques a secret. I've tried to get other builders to put this stuff in, so I tell people how I do it. The code is open source and on Github. With all this stuff, you can pretty much ignore the minor region crossing problems and just drive.

Still get a total fail and have to teleport or reload about every 45 minutes of driving, like everybody else. I'd really like to get that fixed. Biggest immersion-breaking bug in SL. Almost nothing else regularly messes you up so badly you may have to relog. Impacts driving, sailing, flying, large scale roleplay and combat, etc. Come on, LL people. This is embarrassing.

Edited by animats
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6 hours ago, Nalates Urriah said:

 

Snip---Serious sailors and fliers usually have a classic avatar stripped of everything, zero scripts, just for sailing and flying. They also have NO ATTACHMENTS. Only the vehicle is a problem. This gives you the best chance to make a crossing intact. ----Snip

I pretty much do this, although in my case, I make a copy of mesh body and head, and strip the scripts out...My Low-Lag avi weighs in at 300kb …  it helps so much at the crossings. On the odd occasion when I am too lazy to change, and wear a normal avi ( 3-4 mb of scripts ) … I can really feel the difference.

 

 

 

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