tasemulators / genesis-plus-gx Goto Github PK

Note that GameGear games don't need overscan to be enabled, or rather they need it to be disabled because it doesn't make sense for a handheld. So while the option is one for all 3 systems, GG needs to be an exception of some kind and ignore it.

Necessary for camhack encodes (and Sonic TASing if it ever happens) where you need to see your character at all times.

Originally reported by @ScHlAuChi on Discord. There doesn't appear to be a related issue filed upstream, nor in BizHawk's tracker (this core is new after all).

Repro:

1. Load SMS Asterix and the Secret Mission SHA1:DE6A32A548551553A4B3AE332F4BF98ED22D8AB5 in EmuHawk
   • Also affects the Game Gear port SHA1:8AB4EA406A0503B09C1BD89E3217C5735B36EBED, which will show the incorrect behaviour as early as frame ~50—though I had to hardcode GPGX for GG roms as the core preference wasn't being respected.
2. Advance to the start of gameplay (frame ~500 if you spam B1 through the menus)
3. Savestate
4. Loadstate
5. Observe sky is lime green instead of blue (if you have "Use custom backdrop color" enabled, it will be magenta or whatever you've set that to be)
   • On the GG port it's olive green, and the custom colour will override that also.

Affects:

• Genplus-gx in EmuHawk master at TASEmulators/BizHawk@ee0c0a8

Doesn't affect:

• SMSHawk in EmuHawk master at TASEmulators/BizHawk@ee0c0a8

Camhack needs the world to remain in the non-runahead state, so all objects need to have their memory values frozen while we're forcing the camera to go to where the character is.

If the character is way ahead, it takes dozens of invisible frames, because in genesis Sonic games we can't just poke camera to jump to where we need it, it has to be moving there gradually or everything breaks.

So while all this is happening, we need to ensure the world remains frozen so the camera doesn't display things in different places by the time it gets there. Then this could be exposed as a gpgx-exclusive lua function.

My idea has always been having internal memory hooks on the addresses we need to freeze, and on every write occurring from the core, we'd write it back to what it's frozen at immediately.