Not smooth scroll in PAL (50 hz) mode

[diedel]

I did all the tests with the River Raid game (Good MSX version) and Road Fighter.
In my computer the scroll is smooth in fMSX PAL and other PAL emulators like the PUAE for the Commodore Amiga.

Steps I follow:

1. Set 50 Hz refresh under Windows 10
2. In Retroarch -> Video -> Vertical Refresh Rate is set to 50.000 Hz
3. Once the game is running, go to Retroarch -> Quick Menu -> Options -> Machine Type is set to MSX (or MSX2). Just in case I tried also to set VDP Sync Type to 50 Hz.
4. Restart the game to apply the bluemsx settings

You will see hiccups during vertical scrolling. For comparison you can run the same game under 60 Hz or under fMSX core in PAL. In these cases the scroll is as it should be.

[diedel]

After some investigation I find out that changing the Retroarch video driver from "gl" to "d3d12" solves the bug (at least under Windows 10).

[diedel]

Using a Gsync monitor, the Alienware AW2518H, setting the d3d12 video driver workaround doesn't work anymore.

Checking the frame rate output I noticed that is very unstable, the core cannot maintain 50 fps.

There is more, if I disable the Retroarch Audio Synchronization, the core outputs 60 fps, and not 50 fps. This not happens with any Retroarch core.