Héctor Corte

Wonderful submision. I used it to make some geek gif in my blog.
http://thebrickinthesky.wordpress.com/2012/12/23/my-own-death-star/

Thanks. I have fixed that and also the engine now don't stops when pushing another key.

It can be done, but the output of your function is also a 2x2 matrix. There is no maximum defined for that object. You need to define another function which goes from 2x2 matrices into real numbers and decides which matrix represents the maximum (i.e. that function could be something like the sum of all the elements of your matrix).

Very cool game with an authentic retro feel. However I do have two complaints about it:

1. it may be a better idea not to write the code for keyboard handling in KeypressFcn. Because that way you would experience a delay (~0.5 s) after the first keypress. Instead, set a variable to true in KeypressFcn and false in KeyreleaseFcn, and check the status of this variable in the main loop to determine whether this key is pressed or not;

2. The bullets travel too fast. They usually go right through an enemy without hitting it. Possible solutions are 1) slowing down the bullets (less distance per frame, slower apparent speed), or 2) not slowing down the bullets, but increasing the frame rate(less distance per frame, same apparent speed), or 3) using better collision detection algorithm (same distance per frame, same apparent speed).

Anyway, I do like this game. Please keep writing more stuffs like this!

need to move intro() to after spaceship & terrain are initialized