Low FPS in windowed mode when G-Sync is enabled

[vzx]

I'm exploring Ebiten to play around with to create a small game. So far I have been checking out some of the examples and "following along" a little (check the example out, get some ideas, then write something similar in my own project). The project I have currently loads a PNG image and draws it, you can move it around with the arrow keys (translate x/y) and it continuously rotates (every update degrees are incremented, and the image is rotate in the draw).

What I experience however is that it is very slow in windowed mode. The TPS is at ~60, which is great, but the FPS is around ~25-40. This is both with my own project, but also with some of the examples (notable, the rotate example: https://github.com/hajimehoshi/ebiten/blob/master/examples/rotate/main.go).

My computer is relatively modern, with an Intel 6700k CPU, 8GB of RAM, and a GTX 1080 graphics card, and naturally other games run fine on it. The rotate example runs at only 640x480 in a window. My own project runs at 1920x1080 in a window too (my screen is a G-Sync 2560x1440 165Hz display).

My development environment is kind of odd, in the sense that I develop inside of WSL (Windows Subsystem for Linux) and so basically I cross-compile in Linux for Windows, and then run the Windows executable. But I would find it hard to believe that this could have any impact on the performance.

When I set it to fullscreen and the window size to 2560x1440 (my display's native resolution) it works fine however. But as you can imagine it's nicer to be able to play around and check new things out in a smaller windowed mode.

Edit: I played around with the G-Sync settings, and found out this problem occurs when:

• G-Sync is enabled in both fullscreen and windowed mode (see picture below)
• V-Sync is enabled in Ebiten

When G-Sync is switched to only fullscreen or disabled entirely, the problem goes away. Also if it's left enabled, but V-Sync is disabled in Ebiten, it also runs fine.

I changed the issue title accordingly.

[hajimehoshi]

Thank you for reporting! What about the examples on browsers like https://ebiten.org/examples/sprites.html ?

My development environment is kind of odd, in the sense that I develop inside of WSL (Windows Subsystem for Linux) and so basically I cross-compile in Linux for Windows, and then run the Windows executable.

So you compiled your game with GOOS=windows and execute it on Windows, right? When you run the executable, do you execute it via WSL, or without WSL?

[vzx]

Thanks for getting back to me! The browser examples run just fine. I also compiled my own little playground project to WebAssembly and ran it in the browser, also fine (very cool by the way, that I can run a game written in Go in the browser!).

So it really looks related to the very specific case when G-Sync is enabled in the Nvidia control panel for Windowed mode, and the game is running in Windowed mode, and V-Sync is enabled in the game.

So you compiled your game with GOOS=windows and execute it on Windows, right? When you run the executable, do you execute it via WSL, or without WSL?

During playing around, I ran GOOS=windows go run main.go to start the game each time. However I also tried a GOOS=windows go build main.go and then ran the resulting .exe in Windows (just by navigating to the folder and opening it from the explorer).

After I found out it's related to the G-Sync settings, I am convinced that the development setup with WSL is not related to it though. :)

[hajimehoshi]

Thank you for the information!

Unfortunately I'm not familiar with G-sync and don't have a machine with that video card. Then I don't have an immediate solution so far. I'll investigate about G-sync, but any insights are always welcome.

[vzx]

Unfortunately I'm not familiar with G-sync and don't have a machine with that video card. Then I don't have an immediate solution so far. I'll investigate about G-sync, but any insights are always welcome.

Ah, G-Sync is a type of adaptive refresh rate technology by Nvidia, similar to FreeSync by AMD (there's a bit of a long history there). It is a feature implemented in certain displays (usually ones with a higher refresh rate, like 144Hz, 165Hz, 240Hz etc). What it does, is change the refresh rate of the display to the frame rate of the game (or other graphics application) that is running. In that sense, it is kind of the inverse of V-Sync.

As you know, with V-Sync, if the game would normally be running at let's say 100 fps, but the display is only 60Hz, then the game will be restricted to run at 60 fps instead.

With G-Sync, the game runs at whatever frame rate it needs to, and the refresh rate of the display changes to match it. So if you computer is not good enough to run a game well, and it runs at only 50fps, the display will change to 50Hz. Conversely, if the game runs very well and goes up to 100fps, the display will run at 100Hz. The primary benefit of this is prevent tearing, which can happen quite often when a game's frame rate does not match a display's refresh rate (and can be particularly apparent when a game runs at a low frame rate).

The way I understand it, is that for G-Sync to work, typically also V-Sync has to be enabled, to facilitate a kind of feedback loop between the game's frame rate and the display's refresh rate, and to ensure that for example the game will still not refresh faster than the display's maximum refresh rate (eg. not run at more than 144fps on a 144Hz display). But this is also where my knowledge on the subject ends. :)

[hajimehoshi]

Looks like the same problem as #1043