Like fish in a barrel

Managed to fix a few little bugs at lunchtime today. They've all been quite subtle; another carry flag bug plus a case of me using the 6809 TST instruction where the 8080 code expected A to hold the value after the test. Fortunately (well, in most cases it's fortunate) the 6809 LD instruction affects the zero flag so it was a simple case of changing the opcode.

Aside from the shot speed, one of the other bugs I fixed was the damage done to the shields when shot by the player. Turned out that I hadn't reversed the pixel data for the shot sprite or the explosion. That's sorted now and the shields are destroyed in exactly the same way - pixel-for-pixel - as the original.

Both the player laser base (object 0) and player shot (object 1) handlers are still incomplete; the player doesn't blow up and the shot doesn't affect the saucer score or timing. However I'll press on and implement the first of the alien bombs, the so-called "plunger" shot. Once that's done and I've implemented the player being hit, the game will be somewhat 'playable'.

EDIT: I've just realised that I'm not updating the score.. I might tackle that next.

UPDATE: Scoring happens (was implemented, but a bug meant nothing happened) but now you don't get the right score for each alien. It'll have to wait until another time.