X68000 Custom input modes for Retrotink 4K

[incrediblehark]

https://drive.google.com/file/d/1D6TiYw94k1uYfuGHQVhjr0GRjfHLIARc/view?usp=sharing

Linked above is a file containing custom input modes to support the Sharp X68000 on the Retrotink 4K. Below is from the included readme:

To use these custom modes, copy and paste into your current input_database.txt file located in the inputmodes folder on your RT4K SD Card. These were made to address the unknown signal when loading up X68000 software with all of its odd framerates. Some notes:

- These are still a WIP and may not be 100% accurate, but will be a good starting point for people who would like to create custom profiles based on the resolutions. The purpose of the input mode vs a profile is to allow it to be scalable across multiple output resolutions and allow for the creation of profiles based on the input modes.

- Naming convention for these modes are most likely not proper, I went back and forth on these and decided to just do a XXXpXX for the resolution and framerate.

- VRR and frame lock / genlock are recommended for smooth scrolling. If your display cannot do that I would recommend triple buffer and adding 1/2 frame of lag to get less stuttering.

I have tested these on multiple X68000 resolutions to get as close as possible, but I am in no way an expert. Most of this I learned as I went. If you see any issues with these please reach out to me and I'll do my best to fix them. My hope is for these input modes to be implemented into the RT4K firmware one day.

One other note - some of these modes may look squished on your display - don't forget that the X68000 had wide and narrow resolutions for some games that would be adjusted on the monitor itself. Use a 16:9 aspect correction on these to get a better scaled picture.