Finally got to work on this a little this past week, and I made a little progress, and ran into some stumbling blocks. There are some screenshots below As of right now, my biggest issues with this are:
1) How to do the shields, and have them 'break away' piece by piece. I am assuming they have to be sprites(like the ufo and player) instead of cells from a character set (like the invaders), but I haven't a clue how to start it.
2) The left and right edges. Being that the screen is being manipulated to give the illusion of the invaders 'marching', I'm wondering how I'm going to know when a left-most or right-most column of invaders are completely cleared. I need to know this because any time an outermost column is cleared, the remaining invaders now march to that edge. So the edge boundaries need to be moved, in effect. hmmm.... Keep an 11 member array of the invaders, (think of the invaders on their side), and when the first or last members equal zero I'll know an entire column has been destroyed... maybe...