I left integer scale turned off so that the image, whether vertical or landscape, reaches the edge of my Arcade1Up 17
Just be aware that not enabling integer scaling is not recommended because it will cause gfx issues due to bad nearest rounding, those gfx issues being more or less noticeable depending on the context.
Great. I did not know that. Thank you for the heads up!
I changed the bottom line to mame2003_tate_mode = "enabled" which ultimately resolved my issue. now The vertical game is finally displaying the way it should on my HAPP Vision pro monitor mounted vertical !! At some point I'd like to build a vertical only list of games and have the menu / retropi running exclusively in vertical mode.
I knew it would change your life. I would not recommend trying to make the whole of retropie itself work in vertical mode yet, though. I stayed with my rotating monitor because rotating emulationstation causes performance issues. I believe it also became more difficult to rotate emulationstation on the Pi4 because the option was deprecated. I stayed with my Pi3b for my vertical MAME games for that reason and hope that a good solution for a fully vertical system presents itself later.
I thought I had been setting the rendering resolution of the game.
What I had actually been setting was the Pi video output resolution over HDMI to the monitor.
So in the end I now have my games running properly. They are being rendered at 640x480 in the emulator as they should, and I'm outputting dreamcast games at 720p to get a bit more performance. Every other system I left at the default output of 1080p.
Yup, I just set up a clean RetroPie 4.7.1 card, and the defaults give full 4:3 for Snes.
Not for Megadrive though: for the lr_genesis_plus_gx default configuration the game image is not quite 4:3 - skinny black bars at left and right. The default config probably wants aspect_ratio_index=0 (for 4:3). Or a little overscan?
i wouldn't want to make assumptions. it could be true to the real hardware. you'd have to drill into the core options and/or the code, but since we use 'core provided' as our default, and generally use default core options, the default aspect ratio is at the discretion of the core developer, so it's typically intentional.
@dankcushions well thanks you for assisting me with this one. I eventually got it working by using the USA Rom and, as you suggested, stretching the image to 5:4. it fills the whole screen and looks good. I'll be happy with that solution for now. Happy Holidays.
Playing with the sourcecode, I usurped the 8:7 PAR to be just 8:7 like 4:3. The switch that controls this is a boolean and I haven't the time to change it right now (and then I would need to make a github account to request a pull for the changes).