Galaxian getting close.

More Galaxian (though not a lot) progress and none on Xevious (again).

I've optimised the OSD layer somewhat and it should be adequate for real hardware (not that I've actually tried it yet). It's doing nothing anywhere near as demanding as Xevious, although I'm yet to implement the scrolling starfield. Having said that, the starfield should be a lot simpler than Xevious, in that I can utilise non-zoomed sprites and use wrap which means a single sprite update each scroll. I'll use colour cycling via palette update to blink the stars so again, not a lot more demanding than what is happening now.

The game is playable except for the few bugs that remain in the transcode. jotd is getting very close though, so it isn't too far off being finished. The big challenge for both the Amiga and the Neo Geo is the background 'swarm' sound effect, which changes frequency as you reduce the size of the swarm. I think jotd is going to take the same approach as will be necessary on the Neo Geo (at least without writing a custom sound driver), namely take a number of samples at different frequencies and play them back at the appropriate time.

No eye candy because it doesn't really look any different, just plays better.

Otherwise, no excuse not to get back to Xevious really...

UPDATE: another drop from jotd and it's looking very close now!

Galaxian looking good now!

More incremental progress on Galaxian when I should be doing Xevious. But time has been short and I'm trying to support jotd as far as possible as he did me during Xevious. He is slowly finding and fixing bugs in the transcode and so it's getting that little bit closer to being finished every day.

One thing I forgot to mention is that I've implemented all the sounds that jotd has ripped and added to the core. Almost trivial thus far on the Neo Geo, though I suspect the "swarm sound" may cause some difficulties on the Neo Geo...

I've implemented the bullets. With plenty of tiles to spare I rendered the bullets in every possible position within the 16x16 grid of the Neo Geo tile. That gives me options if I need to tweak pixel offsets for the nuances of Galaxian hardware.

Looking pretty accurate now,
although the OSD is still a quick hack atm.

Having just said that, jotd has made the decision to eliminate the above-mentioned hardware nuances (pixel offsets for different sprites) together with the corresponding core code that caters for them. Not much point adjusting sprite coordinates in the core 68K code, only to subsequently reverse them in the OSD layer.

It's time for me to implement my hacked OSD layer "properly". I'll have to implement dirty tiles and defer the background tile update to the VBLANK ISR as well us tidy up the sprite code.

Galaxian sprites working

Got the sprites working during lunchtime today. Positioning is only a rough approximation atm. When I re-write the OSD layer "properly" I'll make sure it's all pixel-perfect.

Tiles and sprites all done!

They work on the attract screen, but not in-game. It's a transcode issue, not an OSD issue.

Next is to implement the bullets. I'll have to manually render the tile(s). I've already added palette entries for them.

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!?!

Xevious, Donkey Kong and now Galaxian on the boil...

Still yet to work on Xevious as there is another distraction now - Galaxian!

jotd is working on a largely programmatically-transcoded version of Scott Tunstell's very comprehensive RE of the arcade Galaxian. He has the game running on the Amiga, sans sprites, already!

I have updated my tools to rip the graphics and palette, and rendered the Neo Geo tiles. I've created a skeleton project for the Neo Geo, added some stub functions for the OSD functions implemented by jotd, and it builds. The splash screen displays (using the Galaxian font) but the game resets the Neo Geo as soon as it runs.

Splash screen with arbitrary colours

I won't be doing a huge amount of work on this in the short term; just enough to get the game running and displaying to give jotd an idea of how the OSD he has defined is working. Then I'll let him finish off the transcode before I polish it off on the Neo Geo.

Xevious is still beckoning of course...

UPDATE: Galaxian may be put on hold. jotd is using a lot of PC-relative addressing which breaks when I specify .text and .bss sections for the code and data respectively... so it may depend on whether or not he's interested in supporting the Neo Geo...