inactive123
commented
3 years ago I think MGS2 would be a 640x448 interlaced game (or lower), PS2 rarely outputted at 640x480 (non-interlaced) because of the low VRAM.
Some games render at odd resolutions like 512x416, like Final Fantasy 10/10-2. PS2 games and their resolutions are all over the place.
But yes, I believe currently there is scaling being done in plugins/GS that is just plain wrong. You can see similar issues with it here -
https://github.com/libretro/pcsx2/issues/136
What complicates it is that the GS plugin has to often times merge two fields into one output image [for interlaced games I assume] (and some games seem to have specific rules, like I saw Persona 4 mentioned a lot in the comments), so basically it does resizing and scaling already under the hood instead of just passing along a raw frame buffer output image. Basically PS2 games used interlaced video for the vast majority of its games, there were a few that you could enable progressive scan output on but they were rare since only a few TVs at the time supported this.
The PCSX2 core is currently scaling the output image before giving it to Retroarch. Things like aspect ratio, integer scaling, bilinear filtering, and shaders are all user-configurable features in Retroarch that are rendered useless when the core handles scaling itself before passing the image off. Scanlines and CRT filters won't work correctly without a clean output, and It just makes the image blurrier because it ends up being scaled multiple times for no reason.
In addition, I believe it's also reporting the new scaled output resolution incorrectly, because integer scaling is showing moire/shimmering artifacts. Not sure if this varies by game, but in Metal Gear Solid 2, the Retroarch scaling menu shows that the resolution is 640x448, but manually setting it to a multiple of 640x480 fixes the issue, so I believe that the core is scaling to 640x480 but then telling Retroarch that the resolution is 640x448 (at least in this game).