Sprites: bigger and better!

I'm working through the object handlers in the order that they appear in the game. So far I have the following complete; Easter Egg, Barra, Zolbak, Logram, Sol Tower, Grobda (stationary) and the Bonus Flag. You can bomb them, score from them, and (where relevant) they disappear in a crater. The last ground-based object in Area 1 is the Boza Logram, which I haven't done yet.

Fun fact: the Easter Egg is worth 10 points, only because bombing anything updates the score from the object table 'POINTS' element and the (default) value of 0 (after the table was zeroed) equates to 10 points in the game.

Although the Logram "fires" bullets at the appropriates times, the code to spawn a new bullet hasn't been written. Technically that simply creates a new 'bullet' object and isn't strictly part of the Logram object handler once it leaves the opening, so I can say the Logram handler is complete.

It's also worth noting that there are a few object handlers in the code that aren't actually used. These are mainly identical copies or variants of objects that are used. One example is a Logram variant whose firing frequency isn't actually defined, and if used, I believe would use the firing frequency of the last object that occupied that slot in the table.

At this point I've started to work on support for 2x2 tile sprites. All the explosions, and the Sol Tower, comprise 2x2 tile sprites, as well as a handful of other ground-based objects in the game. To this end, I have 2x1 tile sprites (double height) coded and tested. In fact one half of the explosions are right now. That was the easy part; simply setting the (NeoGeo) sprite height to 2 tiles and adding the approriate sprite code & colour. Note that AFAIK, only 1x1 and 2x2 tile sprites are actually used by Xevious.

Half of the explosion (2x1 sprites) is right now

The way I plan to add support for 2x2 tile sprites is to double the number of NeoGeo sprites allocated to the Xevious sprites, and simply chain pairs together to get the double-width element of the equation. There will need to be some tweaking of the coordinate because of the difference in coordinate systems between the Xevious arcade and the NeoGeo, but I'm hoping it won't be a lot of work.

What I do have to be wary of though is the 96-sprites-per-scanline limitation on the NeoGeo. The foreground tilemap layer is currently 36 sprites, the background is currently 37 (active) sprites, and adding the two visible display masking sprites makes 75 active sprites on EVERY scanline so far. Given that there are up to 64 sprites on Xevious, I'm going to have to ensure that NeoGeo sprites are only activated when absolutely required.

That's going to be a little bit of work and probably a few days before I get it working properly. Then I think the OSD layer on the NeoGeo will well and truly be finished.