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Terrain and lag


Rhiannon Arkin
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Hi all

so I heard that rumor that a terrain with hills is more laggy then a flat terrain. 

is there anything to that rumor? 

I have a new sim, and i am fighting to find the source of a naughty lag. can't isolate it yet, but since i have sculpted the terrain a little bit I wanted to double check this rumor about hilly terrain being more demanding on the client, thus creating more lag. 

??

 

thanks for your insight

Rhia

 

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Rhiannon Arkin wrote:

Hi all

so I heard that rumor that a terrain with hills is more laggy then a flat terrain. 

is there anything to that rumor? 

 

By lag you mean low FPS?

It won't be the land, your sim is always the same number of vertices, doesn't matter what the Z is, the number of vertices doesn't change. If anything hills are desirable if they are tall enough they can block the objects behind it, then occlusion happens and your computer draws less. More hills is great, vastly desirable over flat, for occlusion.

* Check your trees first, especially if they use blended alpha. One "little something" brand of mesh Willow tree or Olive tree is especially bad for lag. (Speaking about blended alpha, read some of the posts by Penny Patton and others on things like this)

* Stand in the middle of the sim, with your FPS showing (Ctrl-Alt-1 from memory) and slowly turn. Watch if a certain direction is worse. DO the same from each corner.

* Use firestorm's tempory derender, (Right click, More>, Derender, temporary) to remove all of a certain high alpha item. See if the FPS increases in that direction. Relog and try again. As another way, edit the item and send it up 1000M on the Z. Then you can jump up and remove 1000M on Z to put it back.

* Same for mesh. One popular shabby chic brand comes to mind especially, I won't name them, but I term them as "Laggy Fall".

* Check the texture size of each item, edit and Ctrl-Alt-Shift-T, things with 1024x1024 textures are generally evil for lag.

* if you are game, use Developer>Render Metadata >Octree. This can help a lot, but it's a but hard to decode. Look for a lot of fast moving red, and see what that is.

* Also in developer mode is wireframe. If you have mesh turn that on and look for anything that has really densly packed triangles. Turn off wireframe, Derender, test the FPS.

* Particles, especially with one waterfall from a top mesh maker, are killers, especially if his waterfall is layered.

 

If you get stuck you can contact me in world and I can come and look. As a sim builder I've gotten pretty good finding items that wreck people's performance.

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First thing to remember is that there are different kinds of "lag", gpu based lag that stomps your frame rate, network lag that chokes your connection, clientside lag, server side lag physics lag etc.

 

Having shaped terrain shouldn't cause 'lag' unless the slopes affect physical prims that is prims/objects set to fall/roll/bounce etc. as the physic s engine will be constantly trying to determin how the slope affects them, a physical cube in a conical pit is a really annoying thing, it will bounce forever in worst cases.

 

However, major land editing and building can cause some lag, but that should dissipate as soon as the sim has its next reset.

 

For gpu based lag... crtl+shift+1 is useful, the 'rotate till your fps tanks' method is sound, but also... crtl+alt+t to toggle invisi-squint on, if when you spin around, your field of view is a sea of foggy red... alpha blend LAG city, the redder and foggier it is, the worse it will lag.

 

Classic culprits are:

old trees, new trees by old tree makers, old grass, new grass by old grass makers, trees, grass, shadow prims, buildings with alpha blend 'window' wall textures.

 

Physics Lag... Do not have any phisical prims that you do not absolutely need, if you must have a phiscal prim that's scripted to move (say a patroling shark in your lake) make sure it is not confined, every time your wandering physical prim thing bumbs into a wall or obstruction, physics calulations are performed, the more often it happens the higher the physics time for the sim, and the less script time there is, and menus on things stop working.

 

Sims try to keep the frame time to around 22/23 ms, and will dynamically rebalance script time downwards to manage this if agent time or physics time is too high.

 

It's also worth mentioning that you should never ever use those horrible 'persistent temp rezzer' things, that rerez temporary copies of the same item over and over every 30 seconds, I've seen a sim where some idiot had 30 odd 'fireflies' rezzed this way at the same time, every 30 seconds the whole sim would lurch as they all derezzed, and rerezzed, the sim fps and physics fps for the sim took a 60% hit for about a 1/10 of a second every 30 seconds like a damn heartbeat.

 

If you have region/estate rights for the sim, turn off pathfinding, unless you are planning to have pathfinding scripted prim critters roaming about, as pathfinding on sims where the linkset info has not been 'optimised' causes what the LL page on pathfinding refered to as 'performance degredation'. If you don't use it turn it off and save your self a pile of lag.

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Klytyna wrote:

Classic culprits are:

old trees, new trees by old tree makers, old grass, new grass by old grass makers...

As a new tree and grass maker I think I have to thank you for mentioning this. ^_^

I can't agree that what you say applies to all old plant makers though, nor can I say that all recent plant makers are lag concious.

We don't know if the OP's lag issues have anything to do with plants but since you mention it, here are some important rules if you want to cover your parcel with dense vegetation:

  • Alpha masking is essential. My grass fields have a setup script that allows the owner to (among many other things) switch between blending and masking and it's amazing how much difference that makes to the lag level. As a bonus alpha blending also eliminates the dreaded alpha bleeding problem. There is a downside though, alpha masking gives very sharp edges to the plants and can also look bad under low sun morning/evening windlights. Unfotunately there is no perfect solution here.
  • Avoid old inefficient sculpts. No, not sculpts in general. A well made sculpt map is even today often a better solution than mesh for high poly organic shapes like plants and rocks. Unfortunately, three of the most popular sculpt generator tools of the past, Tatara, Prim Generator and Wings 3D are among the big offenders here, Prim Generator because it wastes so many ot the vertices, the other two because they create oversampled maps.
  • Keep it simple. Yes, a dense forest made entirely from highly detailed individual trees can look absolutely wonderful but it comes with a huge cost both in terms of lag and land impact.
  • Think paths and layers. Where are people likely to actually go? Keep the detailed feature plants close to those "paths" and use less laggy plants for the middle distance and background.
  • Avoid meshes with poor LoD at any cost. No matter how careful we are, dense vegeatation will increase the render lag noticeably and that means it's essential to reduce other lag inducers to a minimum. I still think that nobody should buy or sell mesh that can't hold up with LoD factor set at 1. Some other makers feel that is a bit too strict but even so, if the mesh can't hold up even at LoD factor 2, stay away from it.
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I did find a few items i'm baffled by: 

-- some animals... if i look at their LI it says 2, under 'more info' the numbers constantly change, as if these things permanently download. ?

-- a disco ball: same as above. dynamic, constantly loading something. not sure what. 

-- a few palm trees with 8 and more 1k images as leaves. ... 

-- some terrain images were 1k too. i changed them to 512s.

removing those helped for sure to reduce what we perceived as lag. and my red bar in the viewer corner has gotten a lot calmer too. I still feel there's even more i can do. 

If I have this flashing/dancing red bar in my viewer. is there a way of seeing what actually is loading in a more detailed view? 

 

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Rhiannon Arkin wrote:

thanks

I do own the sim, but i can't find an option to turn off pathfinding. where would that be?

I don't think that option exists anymore and besides that "performance degradation" is supposed to be bacuse you can't take full advantage of the NavMesh, not because having pathfinding enabled in itself adds to the load. (But of course, supposed to doesn't necessarily mean it actually is ;) )

You can optimize the NavMesh performance though. If there is a yellow warning triangle in the address bar go to Build-> Pathfinding->Rebake Region.

You may also want to add as much of the sim's content to the NavMesh but simply updating it with the current ground shape can make a significant performance improvement.

But this is server side load and will not affect your fps. ANd that brings up a rather important question: what kind of lag do you have? Lag occurs when one of the links in the chain of computers and connections handling SL can't keep up and to reduce it, we need to focus on the factors that affect the weakest link.

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Rhiannon Arkin wrote:

thanks

I do own the sim, but i can't find an option to turn off pathfinding. where would that be?  

I'm not able to test it, but it's not really accessible as a viewer feature, but rather through the viewer's "Sim Console", invoked by Control-Shift-backquote or (Develop / Consoles / Region Debug Console) -- which is also where you'd restart the sim. According to the wiki article, the command you'd type there would look like:

set dynamic_pathfinding disabled

 

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