Weaknesses in the Ultima IX Physics

Weaknesses in the Ultima IX Physics demonstrates the problems the physics engine of Ultima IX encounters, which are quite a number.

Gravity Trouble
The gravity engine in the game is very badly written. Essentially, items initially try to follow the call of gravity, but if there's anything preventing a perfect fall, the item just gives up on pretending that gravity exists and just sits there. That's because the programmers didn't have the time to program a real gravity engine without taxing the game, which already was at its limit anyway with everything that needed to be calculated. So whenever something is not going perfectly during the fall, the object just ignores gravity.

The effects are quite interesting. Monster drops and/or their remains just hover in the air or seem to be glued to some other object and the scenery (like a slope) in the most strange ways possible. The same goes for dropped objects. Some have misused this broken physics engine for hilarious effect, like building bridges over the ocean with various objects.

The Floating Rune
In addition to that, a very well known problem is, that after cleaning a shrine, nowadays, the Rune and Sigil just hover high above the shrine instead of dropping down as they should. The problem with the floating Rune and Sigil is related to the game not rendering/loading the objects in active memory for gravity to be calculated when these objects are made visible above the shrine. This issue seems to be corrected with enlarging the view distance. Also, this issue has been fixed in a patch for the vanilla game; however, Beautiful Britannia will still have this issue until the next release.

Floating Loot
Indeed, the problem that gravity is generally turned off when an item is too far away or out of sight can be problematic when targeting flying dragons with arrows. Dragons can fly quite high, after all, and an arrow attack adds further distance. Once the dragon is defeated, it often becoms difficult to get the loot, as it floats in the air. This is especially annoying with the dragon at the start of the Abyss, as it holds the key for a chest with blackrock armor parts.



Hanging over the Edge
Sometimes, NPCs or monsters seem to stand on thin air (like over the edge of a ledge) yet they do not fall and also have no trouble to move back on solid ground. The reason is the way collision is detected by the game. NPCs and monsters (and the Avatar) have collision that is not linked the the bodies you see. No, all of them are surrounded by an invisible cylinder that takes over collision detection. Since that cylinder expands quite a bit outward from the visible body, it causes these strange effects.

This is a leftover from the troubled production of the game, as otherwise collision would have been linked to the polygons themselves.

Climbing onto the Scenery
NPCs and enemies often have the strange habit to suddenly appear standing on top of other objects like desks, chairs or chests. This not only looks very strange, but sometimes can even break their AI or have other bad consequences for the scripting in the game.

Two reasons for this bizarre behaviour exist:


 * The pathfinding engine was never really developed, since it was decided that all NPCs stay stationary throughout the entire game and most get teleported if the need would arise. This of course meant that if one still has to move, even a little, it was prone to cause unintended effects.


 * The Z (height) control of the engine isn't the very best, as noted above. This also affects NPCs, but with different symptoms, in that their movements sometimes ignore the Z component and thus they "jump" onto said objects when their place in the world is calculated when entering the area.

Falling through the Ground
This problem haunted the early versions of the game and though patches exist, the programmers never fully managed to get rid of it. Essentially, there's always a chance that the Avatar drops through the floor when the collision detection malfunctions and manages to end up below the game world, standing in a sort of black void. Looking up reveals the game world with a transparent ground (as there's no ground texture on the underside). This pretty much means a reload, as there's no chance to return to normal gameplay.

This can also happen to characters and even if they sink only a little, their AI gets damaged beyond repair. 