SS2 recording demos

[664a33975566aKolya]

Thanks to Luthien for the instructions. (as discussed on ttlg)

To record a demo
1. Put the command "record my_demo.dem" into the user.cfg file in the thief directory (remove the playback command if there's still one in there).
2. Start the game.
3. Play as usual, but don't waste time in the menus since they are recorded too.
4. Press escape and exit the game when the demo is complete.

To replay a demo
1. Put the command "playback my_demo.dem" into the user.cfg file (remove the record command if necessary). Specifying a full path works fine ("playback d:\thief_demos\demo1.dem").
2. If your demos stop working during replay, check out if the workaround described below helps.
3. Start the game, lean back and watch.

Known problems
Unfortunately, replaying is a bit unreliable. When the system loads chunks of the demo into the memory, the playback engine frequently loses the input stream from the file and waits for normal user input again. The following workarounds worked for me:

Workaround:
1. Open the demo in a text editor, then scroll through it from top to bottom.
2. Copy the demo to another place on the disk. This is faster than (1) but uses needs the memory.

In both cases, the file is stored in the disk cache afterwards. Therefore it's not necessary to access the disk when the demo is played. Of course there are no guarantees that this works. If the system is short on memory or other applications are running, the demo may still fail. An automated demo player could read the whole demo file once before starting the game to cache the file.

How the demo recording/replay works
The recording system stores all user input (mouse and keyboard, did not test joystick) and the seed for the random number generator in a file (exactly like a macro recorder). When the demo plays, it simulates that user input. Therefore, the system that plays the demo must likely be configured exactly the same as the recording system. Here is an (untested) list of settings that I believe may influence if the demo works or not:

- keyboard layout (language)
- mouse sensitivity
- sampling rate of the mouse
- mouse and key bindings in the game (user.bnd)
- game version (the mission may have changed)
- language of the game (the length of the conversations is different)
- various configuration settings in cam.cfg, dark.cfg or user.cfg