Foreground and background tile layers complete

Tidied up the display (fixed a few bugs) and finished off the foreground tile layer.

Foreground and background tile layers functional

With both tile layers done (in theory) that just leaves sprites, inputs and - at a much later date - sound for the OSD layer. Undecided whether I'll tackle sprites next, or hook up inputs. Probably the latter as the sprites require quite a bit of infrastructure to be transcoded before I'll see anything of them. With inputs I can code the high level function structure, advance through the attract screens, coin up and start a game.

I was having some technical issues with the Neo Geo implementation of the tile layers using shrinking sprites. Turns out there is a rather unexpected limitation with sprite shrinking which has been confirmed by others. If I had known it would have saved me some frustration. For now I'm working around it, but can come back to that later.

The good thing is that once the OSD layer is in place, it's simply a matter of transcoding the game logic; arguably the hard work will be done.

Thinking more about the Amiga port it occurred to me that there may be issues supporting the rich palette of Xevious. Bugger...