Scrolling complete; only sprites to optimise now!

I'm happy enough with the scrolling on the Neo Geo now so I can move on. I could probably squeeze a few more cycles from the case where the scroll register is updated with a completely arbitrary value, (as opposed to scrolling the screen 1 pixel), but there's no point at all. In fact I had a bug in there which was benign because of the limited scenarios in which this case is executed; I almost didn't fix it (and maybe it's still not right?)

When testing on the AES it is difficult to ascertain whether or not the optimisations have made any difference to the video quality - as the sprites still need work - but it seems to me that there are actually less "sparklies" during the game and the video looks more stable. That could just be my imagination, but it's looking pretty good as-is.

The final piece of optimisation to do is the implementation of the Xevious sprites on the Neo Geo. Unused sprites are not properly deactivated and as a result affect the 96 sprite-per-scanline limit and I suspect also contribute to the "sparklies". And while I'm working on the sprite optimisations I also need to handle flipped double-width sprites properly.

I should note that the optimisations around the sprites are not specially for execution speed, as the core is idle now for between 67%-75% of the frame, and the code I will be optimising is updating the shadow copies of the sprite h/w registers in this period of the frame. So there is bucketloads of headroom on the Neo Geo; it's more about cleaning up the display and minimising the number of active sprites.

Once the sprites are done, that's it for the OSD (Nep Geo) layer (except sound).

I have a list of 8 "gameplay" bugs now; bugs that I would attribute to errors in the transcode of the core rather than the OSD (Neo Geo) layer. A few of them I should to be able to fix fairly quickly, a few others have me scratching my head. But they'll come after the above is complete (and before sound).

jotd has sent me a video of the core running on the Amiga with foreground, background and sprite layers at least partially implemented. It's pretty cool to see it running, and I have no doubt he'll be able to get it going pretty soon! He's also going to help out with the sound.