Hello, I´ve downloaded Retroarch on Windows and I tested some PSone games on Bettle PSX HW with Vulkan, most of them worked pretty great but Gran Turismo 2 is pretty unplayable, in game menus is perfect but in in-game race, the HUD and the cars always Flickers and it runs very choppy, on the Bettle PSX Software it doesn´t have this problem and it runs perfectly, is there a fix that I can do?
No fix while preserving all of the fancy upscaling. I believe you can save a game options file that tells it to use the software renderer instead, though.
oh that sucks because I want to Play GT2 with these fancy upscaling, I guess i´ll wait for a newer bettle PSX core Vulkan that can fix that because it´s the only game that I have problem on the PSX HW core in vulkan
Interesting, I’ve got issues with GT2 when I’m not even using Vulkan. its only when I’m in a race and the other cars are on screen, but its playable on some tracks? if I start to increase anything like the software rendering it quickly go’s from being semi playable to a flashing mess. If you really need your fix GT1 seems to run fine for me 
Beetle PSX in Software-mode should perform GT2 VERY authentic, without big chunks or glitches. At least that is what i have seen in nearly all games i tried. In my opinion games-compatiblity is even better than the latest models of physical Playstation 2 on some games.