Firestorm, like all Second Life viewers, has a large number of configuration settings. One of the most widely misunderstood is named RenderVolumeLODFactor. It’s not at all uncommon for Second Life content creators to tell their users that this should be set as high as possible so their creations can be seen properly.
But what is this magic value, and what does it really do?
LOD stands for “level of detail”, which means in how fine detail the viewer will render an object. A higher LOD means that the viewer will show the object with greater detail than a lower one. A small object rendered at a lower LOD will be shown as a simpler shape; a higher LOD will be rendered more accurately.
Of course, it takes more work to render a complex object then a simpler one, and the higher the LOD required to render it correctly, the harder your computer and graphics card have to work. If there are many objects with high LOD in a scene, your computer will slow down.
The viewer manages this by determining the required LOD based, in part, on how far away you are from the object. A small, complex object 20 meters away can be rendered with a lower LOD, and you’ll never notice the difference, because it doesn’t take up enough space on your screen to show all that detail anyway. If you move yourself (or the camera) closer, the LOD will go up because the object appears larger, and the details will become visible.
RenderVolumeLODFactor controls how the viewer adjusts the LOD based on your distance from the object. It’s used in calculating the actual LOD. A higher value makes the viewer compute a higher LOD, and render objects with more detail, than a lower value would for any given object and distance.
Content creators love to set this value high, so that your viewer shows their creations with all of the details they build in. Some creators recommend numbers in the thousands. This is a very, very bad idea.
Because a higher value makes your computer work harder, raising it needlessly slows your computer down without really doing anything to make things look better. A detail that takes up a third of a pixel on your screen won’t be visible no matter ho high you set the LOD factor. Your computer will still do extra work trying to show it, though.
Not only that, but the calculation that uses the RenderVolumeLODFactor value gives a totally meaningless result for any factor above 10. It won’t crash the viewer, but it doesn’t help matters, and you’re still running the computer much too hard to no purpose.
For the past couple of years, Firestorm has enforced a limit of 8 on that value. We recommend no higher than 4, and will reset the value to 4 if it’s set higher than that. The next release will also give you a warning if you attempt to set it higher than 4.
If you’re doing high-quality photography, then you may wish to set your RenderVolumeLODFactor higher than 4. before you do so as a matter of habit, though, try it at 4 and see if it makes any visible difference. Chances are it won’t.
We hope that creators who tell their customers to use extremely high RenderVolumeLODFactor values will stop doing so. All they’re doing is showing they don’t understand how things work.