I have been playing Pokemon Yellow on an Android GameBoy Color emulator lately. Thoughts about these apps and their model.

• First started with this one: "Gameboy Color A.D"
• Simple app. Easy to use.
• Free with ads in the home screen, not during play time. Ads not shown when in airplane mode.
• All features available in free mode.
• One of them (Fast Forward) wants you to watch a movie before activating it ⇒ skipped in airplane mode.
• Lacks a couple features (Link Mode) + crappy zoom quality (too blurry)
• Tried this alternative: "My Old Boy! Free (GBC)"
• Better quality game.
• Unfortunately many essential features are blocked by a "Only in paid version".
• Load: you can save but cannot reload!
• Link Remote: only in paid.
• ⇒ That was enough of a kill-it-and-uninstall. I think the pure block is not a good strategy as I could not even evaluate the feature. The ability to save without reload is a total non-sense and feels like a bad bait-and-switch.
• There are many many other Android apps for GBC emulation, most of them looking exactly like each other.
• ⇒ My feeling is there are 1 or 2 engines out there and everyone is just repackaging the same thing.
• There is one open source Android version: "Gameboid"
• It seems the original project was open-source and then the original app went paid/closed on Android.
• This uses an NDK z80/gbc emulator source + code around to handle inputs and display and stuff.
• Doesn't seem to support the Link Cable feature which I want.
• I could rebuild an app around this, but is it worth my time? Probably not.
• So for a second I thought about whether I could rewrite the NDK gbc emu in Java.
• ⇒ But surely someone has done it, hasn't it?
• What do I know about z80 assembly code & emulation? ⇒ Nothing.
• What do I know about GBC hardware emulation? ⇒ Nothing.
• ⇒ Again, worth my time trying? Not really.
• "JavaBoy" is one such emulator rewritten in Java.
• Tried it and it builds and run as a Java App in IJ with no problem.
• Source is clean and instructive.
• Most interesting there's a one-file z80 emulator right in there.
• The rest is handling peripherals and magic GBC-specific constants.
• Mentions passes some kind of emulation test + a list of games compatibles.
• ⇒ All this clearly shows I know little on the subject, nor do I really care.

So bottom line:

• Reading the JavaBoy source code, I did learn a couple interesting things on how ROMs & save files are handled (basically they are 8k or 32k memory chunks) and they all tend to load a blah.zip or blah.gb with a side blah.sav for the 32k chunk so that means pretty much all these emulators are cross-compatible if you give them the right files.

Went with the paid version of "My Old Boy!".

• It's disappointing that the Free version can't properly act as good test app.
• Just suck it up and use the 15-min window for trying it out.
• The Link Remote feature worked over wifi + over BT. It's a bit flaky (works fine initially when it goes bad.)
• The app is $4.

It's not worth my time rebuilding my own emu for that price yet I had a fun time looking at the emulator sources and their implementations.