Wednesday, August 26, 2009

Puzzles in horror games. Part 3

In the previous blog some problems with puzzles in adventure games where discussed. It was also mentioned that a major culprit in all of these where that many adventure games do not have a coherent system for doing interactions, like for example a Super Mario game. A nice way of solving this and still allowing a varied set of possible actions might seem to be physics. For the last couple of years, especially after the launch of Half-Life 2, physics have gotten a lot of attention and is pretty much a standard component of any 3D game today. It might therefore seem obvious to start using physics in adventure games in order to bring the genre forward. However, having implemented physics for four games now and working on a fifth a lot of problems have emerged. While adventure games and physics seems like the promised land at first glance, it is far from it.

Difficult controls

Classic adventure games like Myst and Broken Sword got very inntuitive and simple controls and can still give the player a very detailed and varied experience. It is just matter of moving the mouse and clicking to control games, and it is hard to make it more simple than that. For a game using physics, it is much harder. Doing something similar to Broken Sword with physics would be very hard and I have yet to hear an ideas on how it would work. A first person perspective is pretty much demanded in order to have a control system that lets the player perform enough actions to solve varied types of puzzles. This leaves games like Myst and Tex Murphy to use physics. The first person system is also what is used by Penumbra.

However, controls quickly get messy because of something called the z-axis or the third dimension. The problem comes from the main input device, the mouse, working in only two dimension and the actions on screen taking place in three. When manipulating objects this can make things a bit difficult, and in Black Plauge we added the scroll wheel to make up for this. Penumbra was also implemented on a haptic device which allows the user full 3d movement, adding a very nice way of interacting. However, given the current spread of haptic devices, it is not viable to design a system around them. As for other gadgets like the wii-mote, it only has acceleration in 3D, postioning is still in 2D and thus it does not solve the problem.

The problems with controls do not stop there though and the user also wants to rotate objects and do other kinds of manipulation. We added rotation in Black Plauge too and by now the full control system was pretty complex. All of this complexity still only allowed very basic interaction though and attempts to further enhance the interaction could easily lead to something like Trespasser which featured increadibly difficult controls.

The Chaos effect

Even though physics are controlled by a very limited set of rules, because of its complexity, even the smallest varition can cause major differences in outcome. The most striking example of this is the mining cart puzzle in Penumbra Overture. Here the player is supposed to push a cart down a slope to hit a wall, but for some reason, every now and then it would derail and miss the intended target. To fix this, extra forces where added keeping the cart in place and numerous hours was spent at getting it stable. After all this work, the cart can still derail though! In hindsight it would have been a lot easier to just use an animation. This shows how such a simple event can cause tons of problem when physics is involved.

Physics breakdown
Not only does a physical simulation suffer from undeterministic behaviour (chaos) , it can also fail. As hinted in the word "simulation", game physics is not a perfect replica of the real world and can break down at certain points. In the Penumbra games, the best example is that the player can bang objects through the floor if using enough force. Some objects are easier to bang through (because of shape, size, etc) and in Requiem we had make an important object magically appear if it went through.

Sequence breaking

In adventure games, the designer can usually set exactly the kinds of interactions possible with an object and have full control of all possible outcomes. For physics, it is impossible to anticipate all that can happen and one can only test as much as possible, hoping all gaps have been closed. For example: a pit that should not be possible to cross at certain point in the game, might be possible to cross with some ingenius use of objects. In order make sure certain things does not happen we had to add alot of extra checks and hacks in the Penumbra games, sometimes even excluding the player from doing certain actions. This can easily break the sense of immersion, but might be a must in order to have a stable game.

Another type of sequence breaking is doing something "stupid". An example from Penumbra Black Plauge is in a machine room where the player needs a steel pipe as leverage to break open a door. However, there is also a hole in this level and it is possible for the player to throw the pipe down in it. To remedy this, we added several pipes in the level and if the player where to throw them all down the hole, a pipe would magically appear inserted into the door that needed to be opened. It is not very immersive, but at least the game did not break. Luckily, most player seem to not trow imporant objects down in holes.

Player getting stuck
All of the problem listed above can lead to the player getting into a unwinnable situation. Normally physics game have a reset option that lets the player start over. This is crucial for most physics game, for example consider how World of Goo would be if it the player should never be able to end up in an unwinnable state. It would pretty much destroy the entire game.

Adventure games do not have this luxary though and unless one counts some really old games, it has always been possible for the player to continue unless death occured. This restriction ends up making many physics puzzles impossible to implement in an adventure game and when designing the Penumbra games, many puzzles had to be abandoned due to the high risk of putting the player in an unwinnable state.

End notes
I turns out that using physics as a way to bypass the rescritive actions and incoherence of normal adventure game interaction is not possible. Instead adventure games with physics require alot of restrictions and special cases to be added in order to make a working game. It also limits the amount of puzzles that can be used in the game and is not as groundbreaking as it first might seem. This can also be seen in games like Half-life 2 that has not only very few physics puzzles, but also heavily restricted ones. Some physics-like puzzles (for example a large bridge acting as a see-saw) does not even use physics!

Still, given all of the problems with physics, it should not by discarded. It allows for great immersion, which is especially imporant for horror games, and correctly implemented it can make puzzles seem more intuitive and fun to perform. It can also makes it easier to do puzzles with many solutions and make puzzle encounters less frustrating. We will still be using physics for our upcoming game and would like to see more adventure games trying it out!

What is your opion about physics in adventure games? Know any other games with good physics puzzles?