Galaxian on the Neo Geo

Galaxian is coming along nicely! I've only implemented a few very quick hacks to the Xevious OSD layer on the Neo Geo and I can already start and play a game. The tilemap layer is implemented, CLUTs correct, and scrolling working except the offset for the visible display needs tweaking.

Can start and play a game (on FREEPLAY)

Not implemented are the sprites; dive-bombing aliens and bullets & shots. And sound, though it appears jotd has already ripped the sounds and added a few to the Amiga port. Using NGFX SoundBuilder it wouldn't take a lot of work to add them to the Neo Geo as well.

An interesting issue with the Neo Geo implementation. On the MVS the BIOS handles coins and you can only query the BIOS as to whether or not there are sufficient coins inserted to start a game. Galaxian, OTOH, reads a raw input port and debounces it over 4 samples. Thus I will need to use the BIOS routines and effectively "pulse-extend" the coin input to allow Galaxian to detect it.

I'm also considering the possibility of supporting a horizontal monitor for Galaxian... I think it can be done - that'll be interesting!!!

UPDATE: Have implemented 'pulse-extend' for the coin input, and can now coin up.

Have implemented all dipswitch settings except SERVICE MODE and my custom cabinet mode.

Have implemented Galaxian sprites, but so far I can't get them to appear on the screen!?!