Vulkan: Frame scaling/resolution issues causing distortion in some games

[ehw]

Title

This issue affects multiple titles, here are a few that I've noticed but there are definitely more:

https://xemu.app/titles/4343000e/#Auto-Modellista CC-014 [4343000e]
https://xemu.app/titles/41430007/#Aggressive-Inline AC-007 [41430007]
https://xemu.app/titles/45410083/#Black EA-131 [45410083]
https://xemu.app/titles/4b4e002e/#Karaoke-Revolution-Party KN-046 [4b4e002e]

Bug Description

Some games seem to produce vertically distorted outputs when using the Vulkan backend that does not appear in the OpenGL one. The distortion appears over all graphics and elements in the frame, and can also affect full motion video. The distortion appears consistently and in the same areas in all content while playing.

Steps to reproduce:
1.) You just have to set Vulkan as your backend while a game is running, games affected by this issue appear to be affected the moment the games are booted.

All screenshots here were taken with the Vulkan backend at native resolution.

Aggressive Inline:
Notice how there are some parts of the Akklaim logo that look edged and uneven. This isn't how it's supposed to look and it looks fine in OpenGL

Black:
The A/B button icons appear uneven and seem to be distorted. The "A" in the word "PAUSE" should be symmetrical but looks uneven here.

Karaoke Revolution Party:

Expected Behavior

The video output of the Vulkan backend should be on par with the OpenGL backend. In this case, the frame resolution/scaling should be identical between the two.

All screenshots here were taken with the OpenGL backend.

Aggressive Inline:
In comparison to the image posted above, take note that the Akklaim logo looks even and lacks the hard edges as seen in the screenshot from the Vulkan backend.

Black:
In comparison to the image posted above, notice that the A/B button icons look fine and don't seem as distorted. The "A" in the word "PAUSE" seems more symmetrical.

xemu Version

Version: 0.8.2
Branch: master
Commit: 02d35be
Date: Wed Jan 1 23:02:35 UTC 2025

System Information

CPU: AMD Ryzen 7 5800X 8-Core Processor
OS Platform: Windows
OS Version: 22H2
Manufacturer: NVIDIA Corporation
GPU Model: NVIDIA GeForce RTX 3080/PCIe/SSE2
Driver: 4.0.0 NVIDIA 566.36
Shader: 4.00 NVIDIA via Cg compiler

Additional Context

I'm not entirely sure how to describe this issue, but it appears as though there is an issue with the output resolution being scaled improperly in certain games, maybe as if it were off by a pixel or two which causes every other 100 pixels to become vertically distorted.

What made me think it was resolution related is that the distortion issue can almost be remedied by increasing the internal resolution. The higher the IR, the less obvious the distortion is. There is still a distortion, however and all games affected by it are affected the same way.