lag hoodoo part two

As we look at the Lag Meter, under the Help menu on most OpenSim/Second Life viewers, we see three indicators. In this post and the next two, we'll look at what those mean, and how a poor, lagged down user can influence them.

The first one is the Client. This indicator is presented as FPS, or Frames Per Second, and is an indicator of how quickly the local viewer is able to re-render the scene. The faster it renders, the smoother and more immersive the experience will feel. For comparison, standard resolution television renders at 25 or 30 FPS, HDTV ranges from about 24 to 60 FPS, standard 35 mm cinema film runs at 24 FPS, and IMAX runs at either 24 or 48 FPS.

The Lag Meter flags any rate below 10 FPS as red, and below 15 as yellow. My personal observation has been that, below 10 FPS, it starts to feel progressively more and more as if I am trying to walk through hardening cement, and appears more and more as if I am moving through a series of slowly changing pages (which is essentially what is happening). Above 10 FPS, it's generally easier to move, and above 20 FPS or so, it begins to appear much more smooth and lifelike. I have also found that in competitive activities, such as sailing and chariot racing (ask me sometime), if the frame rate drops below 15 FPS, control of my vehicle becomes much more difficult.

So, one might ask, what influences the frame rate? Why doesn't the viewer simply render at 25 or 30 FPS, and be done with it? The answer is both simple and complex, and we'll take more than one week to answer it, but the short answer is, rendering an entire scene can be very difficult, and is impacted by anything that increases complexity. A scene rendered on your computer consists of polygon edges (the wireframe), textures, and lighting. This is true not only of the land and prims, but of all the avatars within the view. The viewer must render all of these things as quickly and efficiently as possible. Having few visible prims makes the job easier, while lots of prims, with lots of textures, makes it harder. Static things make it easier, while moving things--avatars, flexiprims, lots of particles--make it harder.

The rendering is primarily the task of the GPU, the graphics processing unit, and it's supporting electronics on the graphics card. This is an area in which all are definitely not created equal. Take a look at this somewhat outdated http://s3.amazonaws.com/secondlifegrid.net/frameratesbygpu.png (comparison of frame rates by GPU) document. This is specific to older versions of the Second Live viewer, and does not include some of the newer graphics processors, but the relative comparisons still hold true. If anything, newer versions of the viewers are more demanding, and the typical rates will be lower. The ranges are due to several things, including the differences in simple and complex scenes. Also note that ATI GPUs are typically somewhat slower than equivalent nVidia GPUs, even though in a game such as World of Warcraft they may be much closer. Without going into detail, this appears to primarily a difference in drivers between the two GPU makers.

Second to the GPU, the local computer's CPU also handles a lot of the calculations, and the weaker the GPU, the harder the CPU will have to work to compensate. Third, there is memory caching, in both the graphics card and main system RAM. All else being equal, more RAM on both the system and the graphics card is a good thing, as it allows things to be kept available for quick use, instead of having to be retrieved from the server via the network, or from the local hard disk. Finally, there is the network itself. While network is a separate entry on the Lag Meter, it also affects FPS. A processor, whether GPU or CPU, that is not being given things to process as fast as it can handle them simply cannot work at its maximum potential.

So, given that, what are some quick and easy things we can do to increase FPS? There are things that will only affect the local system, and things that will affect not only the local system, but other users as well. We'll start with the former. I will be using the most current Hippo viewer version 0.5.1 set to the English language for consistency as I describe the options; other viewers and other languages may cause some of the settings to vary, or be differently labeled.

The very first thing to do is to open the Preferences window, either Control-P, or from the pull down menu, Edit->Preferences. Select the Network tab, and move the slider for the Disk Cache Size all the way to the right. This maximises the amount of on-disk storage for textures retrieved from the network. Click Apply. Note that this will increase the disk space used locally. You may not see an immediate increase in FPS, but over time, it should help in areas you frequent. Note: if you do not have sufficient space available to increase this cache by 500 MB, then you really should consider either adding more disk space, or removing something from your system.

The next step is to select the Graphics tab. If you have never made adjustments here, you should see a fairly simple dialogue, with a single slider for Quality and Performance. Unless it is already in the leftmost position, try sliding it one step to the left. You should immediately see an increase in FPS on the Lag Meter (Help->Lag Meter) or the Statistics Bar (Control-Shift-1), at the cost of some of the quality of the rendering. This is because the number of details being rendered is being decreased to reduce the rendering time, and thus increase the FPS.

Next time we'll go into more detail on this tab, but for now, if you'd like to experiment more, tick the "Custom" box. This will open up a number of boxes and sliders that you can test to see what effect they have on your system's performance.

One last thing to experiment with is decreasing the size of the viewer window. Tick the box at the top of the graphics tab, labeled 'Run Second Life in a window', if it is not already. Then try choosing different Window Size settings, or simply resize the window frame. You may find that, at smaller window sizes, you see an increase in FPS.

Until next time, cybernauts, may your lag be low!

~*~
Thoria