That said, the Game Gear's LCD is only 160x144, and the Master System has a resolution of 256x192 (or 256x224 or 256x240, but those modes were very rarely used). In Game Gear mode, this resolution is simply cropped. In Master System mode something more interesting has to be done to scale this down to fit the LCD.
I won't bore you with the details here, but will refer you to a post here on the subject. Using the research, I added a mode to the VDP emulator that would mimic this scaling.
This is old news, of course. I have nothing especially new to report, but I have pretty much entirely rewritten the emulator now (apart from the Z80 emulator, which was fairly well designed). The code was absolutely horrible, and so I've redesigned it to be a lot more flexible and intuitive to use as a library. I've rewritten the standard memory mapper, I/O mapping, and VDP (though I did copy the rasterisation and timing stuff from the old VDP code and cleaned it a little); there's a lot more to do (so far I haven't even reintroduced joypad input) but at least it'll be nicer for me to work with. [smile]
In the meantime, here are some ugly screenshots of what Master System games look like on the Game Gear LCD.