The making of a Boza Logram.

Finished off the handler for the Boza Logram (Dome Array) this evening. It was surprisingly complicated; some 277 lines of Z80 assembler, transcoded to 146 lines of 68K assembler.

The Boza Logram is represented by just 2 bytes in the map data; the type ($2D) and the Y coordinate of the sprite (left/right position on the display). From there, the initial handler creates 4 more objects - another 3 for the outer Lograms and one for the centre. In the process it patches the handler table for all 5 objects with new handler functions, and sets up the sprite X & Y coordinates, states and attributes.

Without going into too much detail, the subsequent handlers are responsible for setting up sprite codes, animating the sprites, firing at the Solvalou, checking they've been hit, and exploding - not unlike other handlers. The centre handler also destroys the outer Lograms when it is hit, and conversely the outer Lograms update the points value of the centre (600 pts down from 2,000) when they are hit. A lot going on.

The Boza Logram is ~277 lines of Z80 ASM

When I was actively working on the RE, I thought the initial handler installed the subsequent handlers in a 'callback' table for each object. At the time I didn't think much of it, and they were eventually all-but-forgotten as I proceeded with the RE.

Of course, when it came time to transcode this handler I wrote the new code to copy the handler addresses into a new 'callback' element of the object table, and immediately realised I didn't know how these callbacks were invoked!?! It wasn't long before something twigged, and I realised the 'callback table' was in fact the main function handler table - these weren't callbacks at all.

I have since updated the RE and the 68K source, but it goes to show that you don't always get things 100% right when doing a static analysis. I'd claim that when, and only when, the transcode is complete, the RE will be 100% accurate and true.

As far as ground objects are concerned, Area 1 is now complete (although they don't actually spawn bullets when firing back). That's 8 distinct object handlers done and dusted. Only ~55 to go (though 16 of those alone are for the Andor Genesis aka mothership)...

Not 100% decided what I'll tackle next; either finish off the 2x2 tile sprite support, handle ground-based objects shooting back, start on some flying objects, or move onto the next ground-based object handler.

FTR the main CPU code (68K) is now around 3,000 lines, the Z80 equivalent is 11,000 lines. If I assume the 68K will end up at approximately half the number of lines, it means I'm about 54% of the way though the transcode of the main CPU code. My gut tells me that sounds about right. I'd also guess that the SUB CPU code is around 95% complete.

UPDATE: just added a build option to display the area (technically, in base 17) on the bottom right corner of the display.

Fun fact: Hitting the centre of the Boza Logram (first) is worth 2,000 pts. If you hit both it and one of the outer Lograms at the same time (with the same bomb), you'll get an additional 300 pts for the outer Logram. Hitting an outer Logram first scores 300 pts but will reduce the centre value to 600 pts.