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hogarth

lod or render distance

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I was originally planning on adding an LOD 'level' to some maps I'm starting to make. Basically it is just adding a lower poly version of all buildings and important things. This takes time to make and pumps up the file sizes, which is what I don't like, plus there are probably conflicts with the system that is already in place which uses lightmaps to replace the textures. Option 2 might be to have each building have a kind of shell, and all the detail is a seperate object on the outside of it (and inside). The detail can just dissapear at long distances. This right now seems better than a real LOD effect, but I can think of a downside. Can anyone tell me their experiences with this and what they think is better about each thing?

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Personally, I've never liked LOD because switching between LOD levels if often quite noticable and the performance benefits are fairly small unless you do really aggressive LOD (GTA 3 probably benefits a lot from LOD but their lower LOD levels look awful). I believe it's usually better to do good occlusion culling and then just not render objects that are at a certain distance from the camera (kinda like clipping except more selective. You don't want entire buildings to just disappear).
LOD was great when the poly count was the main limiting factor. Nowadays what you should worry about is state changes and overdraw, neither of which an LOD system will address.
I think UT 3 no longer does LOD (I dunno if its predecessors did), but Crysis still does. Crysis however has an insane draw distance and an insane amount of vegetation geometry so they might actually benefit from it quite a bit.

Another option is to use impostors where you replace objects at a certain distance with a billboard that you generate dynamically. This has two advantages: the billboard geometry usually consists of only two polygons and the shader for rendering the billboard will be super simple. I would guess that writing an impostor system is quite difficult though.

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That was helpfull thanks. I will be using LOD, it's required for prety much anything decent, at least on my hardware. It is definately a balancing act to make it less noticible. In many cases I probably will just make little objects not render, but not buildings and such.

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