Continuing a past series of topics (including this one) where @ReignerDeustcher was prominently present, sharing details for a renderer tweak I am planning for Tartar - have eventually decided to take on widescreen resolutions... but without any serious changes in the code.

So the resolutions remain the same (320x200, 640x400), but there is an option to adjust rendered frame size and internal renderer zoom so that the image appears as if rendered for a 16:10 or 16:9 screen size. Combined with Tartar's own optional scaling this allows to fill 320x200 and 640x400 screen fully while accounting for non-square to square pixels translation.

Here's an example comparing how this type of output looks in 640x400 with scaling on (top, unmodified) compared to "conventionally" rendered screen in the same resolution (bottom, adjusted to square pixels in graphics editor). Scaling of font glyphs and weapon sprites is less appealing in 320x200, that's why I am using higher resolution for the example, but the gist is that with a 16:10 monitor the image no longer looks "flattened" when running in DOS with these options on.

For 640x480, 1280x1024 resolutions and also for 16:9 geometry Tartar is unable to fill the screen fully (it still only has x2x2 and x4x4 integer scaling and can add x1x1.2 vertical scaling for pixel size correction on top), but these are still handy for adapting to actual attached display size while using an emulator (as long as it allows customization of video output's scaling/cropping). Here is a video of Tartar running in 1280x1024 resolution with 16:10 option selected, output scaled and cropped by RetroArch for playing fullscreen on a 1920x1200 display.

https://www.youtube.com/watch?v=uPrYismnPE4