Performance Issues in the Sky?

[MoldyLocks]

Does it matter at what level, meters-wise, you place your skyboxes as far as overall performance goes?   Does having a skybox with lots of objects work better lower to the ground or higher up?

[Rolig Loon]

Your graphics card will try to render anything that is within your draw distance, and will try to render the highest LOD that it can, given the limits you have set in Preferences and debug settings. If you are reasonably far from ground level, there are likely to be fewer things to render, so your FPS should be greater.  Of course, your system will always try to render nearby objects first, so if you have a skybox jammed with stuff, that will affect your performance more than how close to the ground it is.

[Lindal Kidd]

Yes, it matters.  The critical height is 1,000m.  Above this height, the viewer does not render anything that's on the ground, including the ground itself.  This increases viewer performance by a significant amount.

[Nalates Urriah]

All good answers. I'll add, there is an aspect to height where another performance issue come up. It is appearance, which degrades.

Regardless of draw distance (DD), the viewer does render the ground. You can try that out. To test fly up to 100m or 200m and change DD to values less than those. Once up to Lindal's 1,000m that task disappears and you pick up a bit of performance.

Below that 1,000m you are in an area where people fly. So, from time to time your viewer will be rendering those wonderful flying machines. Generally not a problem.

At about 3,000m some other issues come up. The limit is about 4,000m for building. At about 3,000m some items begin to alter shape. You will find people talking about seams appearing in the avatar, mostly from those that use mesh bodies and more so from those that use bodies and heads. People also notice prims not fitting together as they expected.

In these cases they have run into the math problems of 3D real time rendering. While we use floating point numbers for all we do when interfacing with SL 3D space the render engine uses integers. It converts. It is also limited in the number of digits it will use. This causes round off errors. At 4,096.0m building is disallowed (see Limits) because the round off problem is so great. At 3,000m it is a problem that is starting to show. But, is generally acceptable and mostly unnoticed.

So, the sweet spot for skyboxes is the 1,000m to 3,000m range.

[Chic Aeon]

Also around 3000 meters and higher some graphics cards produce an odd black to texture flicker issue on meshes with faces that are close together. Something similar to the alpha sorting, the computer seems to have difficulty figuring out what face is showing . Not an issue with the way the mesh was made, it happens most often on thin planes but the same mesh is fine at lower levels. It took me YEARS to figure out what that was --- both on my meshes and those made by others.  

[Lindal Kidd]

48 minutes ago, Chic Aeon said:

Also around 3000 meters and higher some graphics cards produce an odd black to texture flicker issue on meshes with faces that are close together.

And here I thought it was just oxygen deprivation at high altitude.