As you can see, this is pretty much the same things that we used in Penumbra. But I also hope you noticed that it is more streamlined and intuitive. Allow me to explain.
The grab mode is what is used when interacting with objects like books, chairs and pots. In the first versions of the game, we actually had something more like in Crysis, where the object travels to a certain position when interacted with. This did not feel right though, so we want back to more like in Penumbra. We then added a lot polish to this and especially the rotating mode (when holding down a button, moving mouse rotates object). Even though the object is still moved 100% by a physics simulation, it is very smooth and you can be very exact when placing. In Penumbra there was lots of lag, but that is all gone now!
I think I spent a week or so tweaking how the door opening physics works. In Penumbra, you had to make sure to interact with the door at the right place to open it properly, which made it hard to close / open doors in stressful situations. Not so in Amnesia. Here you can click anywhere on the door and it will easy to control it. The way this is done is by estimating how to convert 2D mouse input into 3D forces. As you will never be able to get perfect correlation between mouse and object (you will always loose a dimension), this took some time to get right. The end results feel very nice though and the things learnt for other interaction types such as levers.
A further improvement is that doors will now stay closed / opened. In Penumbra they sometimes bounced back at you, but in Amnesia that is all fixed saving the player from many virtual/real headaches.
Desktop simulator 2000
Opening drawers is a common interaction and another area where improvements have been made. Drawers will now react faster to player movements and it is possible to have more control (in Penumbra drawers could continue sliding after you stopped moving). And just like doors, the drawers will get stay open / closed, without any annoying bouncing.
Spin round, round...
The one interaction that we got most negative feedback on in Penumbra was the wheels (valves, etc). There was the problem of where to interact as interacting at center zero leverage and made it impossible to turn. Also the actual turning movement could be hard to get right. For Amnesia, we have remade the whole system. Now it is possible to interact wherever you like and the movement required is far more intuitive. There is a special system that analyzes your mouse movements and can quickly and correctly determine which way you want to rotate. It can even approximate the speed and there is as good as no lag involved.
We are very proud of the physics interact we use in our games, and it is something we have worked with for almost 5 years now. It is also a very unique method, and as far as we know we are alone at using it. We will not stop at where we are now though, and hope to take physical interaction even further in the future.
Also, I'd like to mention the fantastic Newton Game Dynamics, the physics engine that makes all of this possible in the first place!