Mothership Incoming!

After a coding session today, the mothership is now flying across the top of the screen at random intervals (randomness based on player actions). Points for shooting the mothership depend on how quickly the player shoots it, so the quicker it's shot, the more points are awarded. I was able to tweak the code listing in strategic places to get the ship moving smoothly, so it's good to go & I'll be moving on to the alien gunfire next.

One snag is a bug I've spotted (thanks to my wife's playtesting assistance) that causes the aliens to drop down too soon when moving to the left. It seems to be linked to the status of the eighth column of invaders. The program thinks there is an alien in the eighth column when there isn't, and it only happens when aliens are moving to the left. I've scoured the code and been unable to find the bug, which is frustrating but there are a few more checks I can still run in my next programming session. Fingers crossed I'll find the bug & fix it.