It's definitely possible to completely trap the blocks (try building walls from the entrance up to the first set of spike and closing them in with it). Probably you want to run some search algorithm each time a block is placed to check that no blocks are unable to reach the exit.
Kudos for the linux binary though, and it's a pretty clever idea!
Thanks for playing, I will play your guy's games later when I finish work.
The game does stop you from placing walls that block cubes from finishing, but I coded it quickly before submitting the game, so it probably has some major flaws. I know that it doesn't take the entrance into account, so you can block the entrance, and then no cubes can solve the maze, or if there are no cubes in the maze you can block the exit.
@myachin you can still play on windows. The download is a zip that contains all the source. I've been meaning to compile for windows, but just haven't got round to booting up windows and getting sdl and opengl for it.
The game's pretty challenging - especially with a touchpad - but a few times I did manage to block off the exit completely.
I'm on a 16:10 monitor so the text on the sides was cut off - if anybody else isn't on a 16:9 monitor, I'd recommend reading it beforehand.
This was pretty fun and very technically impressive. It's a nice mashup of tower defense and puzzle games!