Loose items in exterior cells lead to missing land

[InAComaDial999]

So yesterday I was attempting to diagnose a bug in my game. The symptom was that when I approached Fort Magia from certain directions, the entire cell in which it is located would fail to load, leaving a big rectangular hole in the landscape with just a few items floating in the air. After some poking with TES4Edit and turning mods on and off, I discovered that the problem went away if I disabled the UOP, which modifies that cell. However, upon further testing, I seem to have discovered that the problem occurs not because of anything specific that the UOP is doing, but because of a general engine bug.

 

The bug seems to be this: loose non-static items get havoked when the cell they are contained in is loaded. Normally this is no problem, though poorly placed items can sometimes move around. But if the item is placed near a cell border, and if the item havoks its way across the cell border into an as-yet-unloaded neighboring cell, the contents of the neighboring cell will never load.

 

What led me to discover this was that when the bug occurred with Fort Magia, there was a set of three loose items stacked floating in the air in front of the fort door ( picture here ) and a few items right on the border with the neighboring cell. Those items are normally located inside a small ruined tower ( CS pic here ). Looking in the CS, I noticed that the border between the Fort Magia exterior cell and its neighboring cell passes right through the center of that tower ( picture here ). And the items that were floating in front of the Fort Magia door were all ones placed in the neighboring cell, not in the Fort Magia cell itself.

 

I "fixed" the problem in the CS by moving all of the items into the Fort Magia cell, but still in the little tower ( pic here ). That prevents the problem occurring, because the offending items don't get loaded until the cell containing the Fort gets loaded. But... yup, you guessed it: if I approach the area from across the water, the opposite problem can occur, and the cell next to Fort Magia can now fail to load, leaving a big hole there instead.

 

I decided to make a more general test. I made a trivial mod that places a big rock in Wilderness (17,13) right on the border with (16,13) such that part of the rock extends into (16,13). Then I placed a skull in (16,13) that sits on the protruding part of the rock. Sure enough, if I approach the area from the (16,13) side, the skull rolls into (17,13) and there's a big square hole in the ground. So the problem is definitely reproducible.

 

My suspicion is that the items getting havoked into a neighboring cell causes the game engine to mark that cell's contents as already loaded. So, when the player moves closer to the cell, the engine doesn't draw the cell contents because it thinks it doesn't need to. There is also some interaction with mods in all of this; it only seems to happen when a mod edits the contents of a cell. I also noticed that any items that are modified by the mod do get drawn -- you'll notice in the pic I linked above that there are a couple of rocks and a tree in the otherwise empty Fort Magia cell -- those items are the ones that the UOP moves. Everything the UOP doesn't touch, doesn't get drawn.

 

Anyway, I thought I'd share, as I think this may explain some of the weird missing-landscape issues that plague certain areas in the game when mods make changes to cells in those areas.

[David Brasher]

I think the problem is more widespread than mods. It can be caused by savegames and actions you take in your playing. So if you kill a bandit and he drops his shield and sword on the boundary between two cells, a cell could fail to load on a random basis. The sword and shield might get knocked around by people walking, or someone may decide to pick up the sword.

 

I have recently experienced problems of this nature on a road that is horribly littered with weapons and armor from the hoards of bandits and others that have died on this road. If a hole appears in my game world, it usually goes away if I exit and reload.

Edited December 11, 2010 by David Brasher

[InAComaDial999]

I think the problem is more widespread than mods. It can be caused by savegames and actions you take in your playing. So if you kill a bandit and he drops his shield and sword on the boundary between two cells, a cell could fail to load on a random basis. The sword and shield might get knocked around by people walking, or someone may decide to pick up the sword.

 

Definitely. And loose items in the wilderness always experience "cell-load havok". That is, unless they are lying on a perfectly flat surface or at the lowest point in the landscape, they will move around randomly. So this can happen even if nothing ever actually interacts with the items.

[effeob]

I think the problem is more widespread than mods. It can be caused by savegames and actions you take in your playing. So if you kill a bandit and he drops his shield and sword on the boundary between two cells, a cell could fail to load on a random basis. The sword and shield might get knocked around by people walking, or someone may decide to pick up the sword.

 

I have recently experienced problems of this nature on a road that is horribly littered with weapons and armor from the hoards of bandits and others that have died on this road. If a hole appears in my game world, it usually goes away if I exit and reload.

 

 

i have this same exact problem - cell next to fort magia, and somewhat slicing right through part of it, doesnt load at all...big rectangular hole.

any known fix for this? as its obviously UOP thats causing it?

[Lanceor]

It's not actually the UOP that's doing it, but an engine bug. Any item rolling or falling into an exterior cell before the cell has loaded can trigger the bug.

 

I'm not sure if this will work, but it's worth a try. Move well away from Fort Magia (preferably into a town or dungeon) and in the console, type "pcb". With a bit of luck, the cell will reload properly when you visit it again. If it doesn't work, try it again but approach Fort Magia from the other direction.

[InAComaDial999]

It's not actually the UOP that's doing it, but an engine bug. Any item rolling or falling into an exterior cell before the cell has loaded can trigger the bug.

 

Yes, like I said, it's an engine bug and not specific to the UOP. However, it does seem as though it only happens in cells that are touched by mods. I have never seen this happen in unmodded games.

 

The current version of the UOPS has changes that address the known issues like the one at Fort Magia, the one under the bridge south of Bravil, etc, by moving the items that tended to roll into neighboring cells. These seem to have cured those particular manifestations of the bug, though of course it can still happen due to items placed in the world during the course of play (e.g. items dropped by dead bandits).

[lgpmichael]

Well, that IS interesting. Id never have guessed that is what causes it. Ive seen it no end of times on the road between Bravil and Leyawiin, and it always only happened when heading south... I'll have to fire up the CS and see what I can see now.

 

Good catch!