I love this core, thank you.
On my 16:9 HDMI monitor, the Workbench looks perfect, but many games appear quite small because games often don't use the full screen. There's nothing really wrong with that, after all the original Amiga also displayed these large borders in games.
But modern 16:9 screens have so much screen real estate. And we have these great HDMI filters like "bilinear_sharp.txt" now in Mister. Maybe a zoom mode for Amiga, similar to what we have in the C64 core, would be possible?
Since different games use different vertical screen areas, a zoom mode percentage and vertical offset option would be best. So things are a bit more involved than the fixed zoom on C64.
Here are the vertical lines for zoom modes I have used before in the UAE4All2 Switch and Vita emulator:
For vertical offset, e.g. first displayed line, I used 0, 18 or 30. That covered most games. To cover all games, a quick option to move the screen up and down to center it with the dpad or cursor keys would be even better.
The vertical lines displayed should be zoomed to cover the vertical screen size (1080p on my monitor). The horizontal size is then determined by forcing the pixel aspect ratio to be correct (1:1 on Amiga?).
I have no clue how difficult this would be to implement into the current core. But since the C64 core already has a perfect zoom mode (I love it!), maybe a zoom mode for Amiga is also feasible?
In latest Retroarch PUAE core, the GitHub user Sonninnos managed to even implement an autozoom. It looks for first and last non-black raster line, and zooms and centers accordingly. This seems a bit involved though, and would probably harm performance.