One crucial point about the projector is that it can be used by anyone (anyone being, namely, the friend who put money in the project). Used by anyone means having a graphic user interface. That was one of the reason I first choose Python for the user side code : Python has several tools and environment at hand.

But Python was let aside because of computation speed, and C choosen instead. And choosing a developpment environment for C with GUI was not an easy task.

At least till I cross the path of Qt. Qt has an embedded powerful GUI tool which can be use to graphically design windows and containing every kind of display object you could need. And it also has libraries available for almost everything you could need in your project, from basic file parsing to image or vector manipulation, audio playing and streaming, serial or network connection, etc. And it is extremely well documented !
So, Qt. One problem though was cross compilation, which is possible, but I didn't succeed in cross-compiling for window (why don't everybody use Linux, I still wonder ! :D )

But, there was this problem with audio hardware not being the same on every computer, so, switch again to another solution... Anyway, I'll probably use Qt again if I need to run a program with a powerful GUI. It really make thinks easy when developing complex applications.