Add RetroAchievements support

[nfp0]

All bsnes and higan cores in Retroarch, besides this one, support RetroAchievements (even higan Accuracy and nSide Balanced, contrary to the info in the docs).

It would be great to have this excellent up-to-date core also supporting RetroAchievements. Maybe code from the other bsnes/higan cores can be ported to this one to save time.

[nfp0]

According to a contributor, the missing implementation is this:

bsnes/bsnes/target-libretro/libretro.cpp

Lines 711 to 721 in 30e2749

	// Currently, there is no safe/sensible way to use the memory interface without severe hackery.
	// Rely on higan to load and save SRAM until there is really compelling reason not to.
	RETRO_API void *retro_get_memory_data(unsigned id)
	{
	return nullptr;
	}
	RETRO_API size_t retro_get_memory_size(unsigned id)
	{
	return 0;
	}

[Screwtapello]

I don't know enough about the libretro API or bsnes' internals to guess why that comment describes it as "severe hackery", but it does seem it would be nice to have as an option.

If it's possible to implement this feature without "severe hackery", I'd accept a PR. If not, I would be interested to hear an explanation of the scope of the hackery required.

[nfp0]

That comment also confused me. The problem is that I don't know how to track who wrote that comment. And the comment is so old that it might not even be valid anymore.

From a quick look-around on the code of the old bsnes cores that support RetroAchievements, it seems to be a straightforward implementation.
Here are examples from 2 different bsnes cores:
https://github.com/libretro/nSide/blob/5e965d0db4c0d05e7e8fb6449035538781c73473/nSide/target-libretro/libretro.cpp#L334-L346

https://github.com/libretro/bsnes-libretro/blob/6d2c3a811c09ffa5d00f50c1491975f1e480fffa/target-libretro/libretro.cpp#L1033-L1108

[Noxillio]

I wish this would get more attention.
I'd help out but I don't know anything about emulators or the technical side of RetroAchievements.

[Sanaki]

If memory is exposed properly, you shouldn't need to know anything about RetroAchievements for it to work. Achieving that without breaking or slowing down everything in this core would require quite a bit of programming knowledge though.

[Noxillio]

this core

It's not a core though, right? This is its own emulator. But then again, I don't understand the technicalities of RetroArch cores either so if I'm wrong about that please tell me.

Also, this might be asking too much too, but it would be absolutely perfect if it would also support Game Boy titles via Super Game Boy emulation. It's the whole reason I use bsnes, because it's the absolute best way to play Game Boy games.

[Sanaki]

Oh, bugger, misread the repo. Thought this was in the libretro core's repo. I'm following too many of these, sorry about that. Then yeah, this one would need to implement rcheevos. But again, the big difficulty is in memory exposure. If someone -does- want to take on the task, I'd be happy to help go over requirements and such, and you can always contact us through the RetroAchievements discord server if need be.
https://github.com/RetroAchievements/rcheevos/

[nfp0]

There's a comment from @hunterk (don't remember where) where he mentions that this is not as simple as it looks, but I would like to have some insight on why it would be complex.

If it's nothing outside of this world, I might dive into it.

[hizzlekizzle]

IIRC, the issue is that the memory pointer lives inside of a struct that lives inside another struct and unrolling it enough to access it directly would make quite a mess of things.

EDIT: and to be clear, this wasn't the case with previous bsnes iterations, which exposed it easy-peasy.

[nfp0]

Aw shame. If that is the case I guess we'll be stuck with bsnes2014 for a while.
Thank you for the insight @hizzlekizzle !