A Moogle  🏳️‍🌈 💻 🎮 🎶 🇸🇪

Looking at some old arcade platformers, I never noticed before how nasty the scrolling is in Bionic Commando (1987), 30fps is nasty for scrolls, blurs whenever you move, this looks like jerky 20fps or lower. Running on a 10MHz 68000 at only 256*224 too, would expect 60fps.

It'd be interesting to see what hardware it runs on, it's as though it's software scrolling rather than hardware though this seems weird for 1987.

Let's find out together! First things first, we pop open src/mame/drivers/bionicc.cpp and have a look at the machine config. In this case, it's even worse: The 68000 is 12MHz! https://github.com/mamedev/mame/blob/master/src/mame/drivers/bionicc.cpp#L375 …

Based on line 400 - MCFG_DEVICE_ADD("spritegen", TIGEROAD_SPRITE, 0) - we see that it uses Capcom's "Tiger Road" sprite system. But it's pretty simple, and doesn't handle the tilemaps: https://github.com/mamedev/mame/blob/master/src/mame/video/tigeroad_spr.cpp … So, back to bionicc.cpp, let's look at the address map!

These three lines here look promising: https://github.com/mamedev/mame/blob/master/src/mame/drivers/bionicc.cpp#L176 … So it appears we have 4k of "tx" video RAM (whatever that is) mapped at 0xfec000, 16k each of foreground and background video RAM, starting at 0xff0000, and 2k of palette RAM at 0xff8000. On to ../video/bionicc.cpp!

As an afterthought, there appear to be 8 bytes of scroll registers, handled by the handler "scroll_w", mapped at 0xfe8010. Sounds promising, but it must be in src/mame/video/bionicc.cpp, as it's not in the driver source itself. https://github.com/mamedev/mame/blob/master/src/mame/drivers/bionicc.cpp#L173 …

Here we have the meat and potatoes of the video, but pretty stingy meat and potatoes they are indeed - other than the PROM-based priority mixer, it seems pretty straightforward, including scroll_w: https://github.com/mamedev/mame/blob/master/src/mame/video/bionicc.cpp … You're right - the game is probably just badly coded.