Description:
Game performance tanks massively with borderless the game runs at 30 fps in menu and 15 fps in game. Without it runs at 60fps in menu and 60-80fps in game.

Steps to reproduce:

1. Start Minecraft

Versions:

• Minecraft Version: 1.16.5
• Forge Version: 36.0.42
• Mod Version: borderless-1.16.4-1.1.0.jar

Please list other mods that seem to cause the issue.
IDK if they cause the issue, but here's my mod list (i've already removed the borderless mod because I can't play at those framerates :p

I have an Intel Core i5-9600K CPU @ 3.70GHz
32GB DDR4 ram (with 8GB allocated for MC)
An RTX 2080 running at 1440p and GSYNC

I'm seeing the same issue, but only with the MultiMC launcher. It has no issues with the Curseforge launcher, oddly enough.

Exiting and joining another world, the issue persists, only goes away when killing MC through MultiMC

edit, disregard, my issue was due to using OpenJ9.

I can confirm this has an issue with me even on curseforge launcher, and the mod by itself. It seems to be deviated from an overdraw issue where the game has horizontal tearing, even though vsync may be both on and off. Is it possible somehow that the opengl driver or lwjgl is having trouble drawing to a borderless window and understanding when to sync?

I am using java 8 u51 in mc 1.16.5.

The issue is related to GLFW and the fix has to be done in that library, see issue #3 (comment)

I have no time to patch the library by myself and have not tried that yet. You can also track the progress with these patches in the BorderlessMining repo: comp500/BorderlessMining#19.

comp500 has built a modified glfw3.dll, you may have to change it with the one that Minecraft uses until the fixes are in the official GLFW repo and applied by Mojang.

I'll investigate the issue. The mods you've listed are the only thing I can really check, whether they might cause bugs in my mod. Besides that, I currently have no idea why there is such a big performance drawback. I assume that GSYNC or VSYNC on other machines might cause this issue, but I couldn't verify this yet. Your setup should definitely be sufficient. I can't really explain why the performance is that bad.

Thanks anyways for reporting, especially for the mods list.