He's coming! Quick, everybody up on the crosses!
March 19, 2019 8:37 AM   Subscribe

When entering a building or quick-traveling to a location in Fallout 3 or Fallout: New Vegas on PC, I have noticed that sometimes items in the new location either jump from ground level to where they're supposed to be, or appear to be falling to the ground right as I arrive. I'm hoping someone could explain what the game is doing when this happens, and why the game has to generate items and then move them, rather than generating them already in place.

I've noticed this most consistently when quick-traveling to Nipton, in Fallout: New Vegas: if there are corpses present, they start from a more-or-less "standing" position and then collapse to the ground; at the same time, any living Powder Gangers jump up from ground level to the crosses.

Related: the tendency of the game to spawn objects that hover above the surface they're supposed to be resting on. Often several objects will be hovering simultaneously, until you take one, at which point the others will fall onto the surface.

I assume that this behavior is an artifact of the way some other problem was solved by the programmers, but I'm curious about what problem, specifically, would require objects to spawn this way.

Bonus question: I would love to find a forum or blog or etc. that explains how video games work, mechanically. For example, a while back there was an FPP that linked to a step-by-step explanation of the graphics rendering in Doom (2016), which was written at more or less exactly the level of knowledge I can understand.

Bonus bonus question: I'm particularly interested in explanations of the inner workings of Half-Life 2, Dishonored / Dishonored 2, Prey, Deus Ex: Human Revolution, and the aforementioned Fallout games. Literary-criticism-type writing about these games would also be valuable.
posted by Spathe Cadet to Sports, Hobbies, & Recreation (8 answers total) 3 users marked this as a favorite
Best answer: The game engine used in Fallout and Elder Scrolls games is notorious for its bugs. The physics engine is a relatively late addition, and it often fails pretty badly.

The problem of corpses suddenly collapsing is probably because the game hasn't bothered to save the precise crumple-state of every corpse. When you fast travel, the game has "forgotten" where all the corpses were- it knows there's a corpse here, a corpse there, but the physics state is missing. So they all just collapse from scratch again. This works okay when you don't fast travel, but if you show up "too fast", they haven't finished collapsing yet.

It might make sense to just delay loading the level until the physics has been turned on for a bit, but that makes loading slower.
posted by BungaDunga at 8:52 AM on March 19, 2019 [3 favorites]

Best answer: As to objects not having physics until you poke them, and suddenly everything falls to the table. This happens because level designers don't design with physics turned on; they are just placing objects. So often objects aren't exactly placed on top of the table- they can hover a little bit.

When you enter a level, it doesn't run physics on every item to save processing power- who cares whether a lamp halfway across the map is hovering a little bit?- but when you interact with an item, nearby items "wake up" and start having physics. So combine the two, and you'll find the problem you noticed. You could solve this problem by pre-running physics to drop everything before, but 1) that would nudge every designer's carefully placed items by a bit, and 2) it doesn't seem like a problem that the game publisher really cares about.
posted by BungaDunga at 8:56 AM on March 19, 2019 [2 favorites]

Best answer: The overarching reason is that physics is a second or third thought when it comes to Fallout games. In Half Life 2, or Portal, physics is a key part of the game. In Fallout (and other games that use the same engine), physics is basically a toy feature they throw in just because people expect it in modern AAA games. The devs don't really care much whether a corpse falls realistically, or whether the world is full of objects that are very slightly floating.

You could have a perfectly good Fallout game with no corpse physics at all- just have every corpse run the same pre-calculated "oh no, I'm dead" animation and topple over. Miscellaneous items could just stay where they're put and not roll around when you shove them, and you'd have a working universe with much more simple physics. But you can bolt on a good-enough physics engine and add a few more ways for players to entertain themselves, so that's what happened.
posted by BungaDunga at 9:06 AM on March 19, 2019 [2 favorites]

Best answer: Also, the collision physics in those games do weird things if objects intersect in ways they shouldn't. It's probably easier when making the level to place things floating slightly and let the physics engine drop them, than to place them exactly on the surfaces and risk small errors causing your dining room set to explode when you enter your great hall.

As happened to me when I tried to decorate my house in Skyrim.
posted by mrgoat at 12:53 PM on March 19, 2019 [4 favorites]

Best answer: I'd suggest looking for videos on "Fallout Creation Kit" to see how things are created.

I'd also recommend Robert Yang's Level With Me YouTube series, which talks all about level design in various games, including Half-Life 2.

I've used the Creation Kit to make mods for the Fallout games; you can see exactly how the Bethesda level designers left things. They certainly don't leave things in mid-air. But, there are thousands of items in the game. When you add an item to a room, you generally drop it into place. But (say) you might move the table it's on later, and forget to adjust all the items on top of it. In-game, they'll settle down when the room is loaded. Or better yet, when their region is disturbed.

I think BungaDunga's right about the corpses. They're not going to record where each joint of the ragdoll (that's the cute technical term for dead people in video games) ended up. They'll just remember roughly where it is, and let the physics kick in to let it settle down.
posted by zompist at 10:50 PM on March 19, 2019

As a player hack, I make a point of muttering "I've really got to cut down the chems!" whenever I see a game glitch. ie pretending your character is hallucinating goes a long way to ignoring the glitches.
posted by Mogur at 4:48 AM on March 20, 2019

Response by poster: Mogur: The glitches don't bother me; I actually find them kind of fascinating, because they're hints about how the game works and the way it models the world. (The glitches that bother me are the ones where I'm thrown out of the game world because it's crashes to the desktop. Those happen a fair amount with F3 and FNV too, alas.)
posted by Spathe Cadet at 7:29 AM on March 20, 2019

Possibly a little to the side of this request, but I'd suggest looking at advanced base-building tutorials for Fallout 4. Especially look for videos on the "rug glitch" and "pillar glitch." Because the base-building has to use the in-game engines and tools, the techniques that people figure out to do more and more creative stuff in that mode can lead to fascinating insights into things like snap points, collision boxes, etc.
posted by oblique red at 9:33 AM on March 20, 2019

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