Vulkan has been broken with the Flycast core since version 1.19.0

[PoloniumRain]

Description

When using Vulkan with the Flycast core, there is significant graphical corruption in all Dreamcast games in the form of many small flickering blocks, as shown in the videos below. At first i thought this was a Flycast problem so i posted about it on the Flycast GitHub. But after much more testing i've now narrowed this issue down to a change that was introduce with RA version 1.19.0, and it still persists in version 1.19.1. All older versions like 1.17 do not have this problem, at least going back to 1.14, which is the oldest that i've tested.

Some things of note:

• I can't test the latest RA nightly (7th August) because it crashes immediately after running any game with Flycast + Vulkan.
• The graphics corruption happens with several Nvidia driver versions, going back ~7 months (haven't tried any older than this).
• The standalone Flycast emulator works completely fine with Vulkan.
• Default settings were used for RA and the Flycast core.
• I don't have anything running in the background that could be causing this.
• It's not just games, corruption also happens on the Dreamcast menu that appears when a disc isn't inserted in the console.
• The type of graphical corruption looks similar to when VRAM on a graphics card has been overclocked too high. So i must stress that my card isn't overclocked and i've done many stress tests to make sure it's not a GPU related problem.

Steps to reproduce the bug

1. Set the video driver in RetroArch to Vulkan
2. Go to Online Updater > Core Downloader and get the latest Flycast core
3. Run any DC game and you should now see the same issue as shown in the videos below.

Version/Commit

RetroArch stable 1.19.0 and 1.19.1 are both affected.

Environment information

• Windows 11 version 23H2
• RTX 3080 with several different Nvidia drivers
• 4K desktop resolution @ 120Hz refresh

https://github.com/user-attachments/assets/6939e144-5cd7-45d6-a77d-e3ee96b9e287

https://github.com/user-attachments/assets/866d1c79-c77f-41af-b80d-cd1bd714d51c

https://github.com/user-attachments/assets/da6b4ccd-6d17-43ca-9350-3cbbb2485e17