Alt-tab while in exclusive fullscreen takes longer than expected

[peppy]

Reported twice now, hitting alt-tab while in exclusive fullscreen mode seems to switch display modes more times than required. Will require some investigation by someone who can reproduce this to find out the origin of the issue (osu! / osu-framework / sdl). Apparently stable does it well, for whatever that's worth.

There have been a few recent issues made SDL's end surrounding the fullscreen logic. This one for instance may be related to what users are seeing here.

Discussed in #17380

^{Originally posted by Rian8337 March 21, 2022}
I've had this problem ever since I tried osu!lazer, but didn't bother asking as I didn't find this annoying. However, it started to bug me out nowadays that I'm playing the game more often than osu!stable.

Unfortunately, I didn't have a good enough computer nor device to record, but I thought the video is enough to give an idea of what's going on (had to put it on YouTube due to GitHub file size limit).

In case it's not clear, I was simply alt-tabbing between Notepad and the game, which caused both my displays to flicker. I'm not sure if this is a problem on my end or the game, so I didn't immediately create an issue.

Logs:
network.log
performance-update.log
runtime.log
updater.log
database.log
performance-audio.log
performance-draw.log
performance-input.log
performance.log

[Susko3]

Can repro this when running my monitor (1920x1080@60) at non-native resolution. Enabling GPU scaling seems to fix it.

I'm guessing that a wrong display mode is chosen, and enabling GPU scaling forces the correct mode.

[peppy]

Weird thing is that it still is taking more display mode switches than stable, as of a recent SDL change. I have a feeling it's related to the constant changes around these code paths in SDL (maybe libsdl-org/SDL#5509 or one of the countless other issues reported) so we'll probably need to continue to bump SDL and watch for improvements/regressions.

[caesay]

As far as I know, there's very little benefit to entering/supporting fullscreen exclusive mode on modern windows with DX11 or higher.

If you are borderless, using a DXGI_SWAP_EFFECT_FLIP_DISCARD swap chain with 2 buffers, and your buffer is the same size as the display you're rendering on, the DWM will let you enter "Hardware Independent Flip" where your swap chain back buffer is flipped by the DWM directly on to the display front buffer when you Present. This will give you performance as-good-as exclusive or in some cases better, and it's the recommended approach as of DX11.

https://github.com/GameTechDev/PresentMon is a great tool for debugging what display mode you're in (Hardware exclusive, hardware independent flip, etc). If you are seeing GDI Copy or Composed, your swap chain is probably not configured correctly.

I don't know how this is handled in SDL, just thought this might be useful.

[peppy]

Right now we are limited by the fact we're using OpenGL for rendering pipeline. Work towards getting Direct X and vulkan online is being done, at which point we'll definitely want to look at that as an alternative.

[AeliusSaionji]

A workaround for the meantime: Special K has a translation layer which takes opengl calls and presents them using d3d11, for the specific purpose of granting opengl games hardware independent flip. This also allows gsync to work.

Independent flip while osu is focused

Benefit of independent flip is you may alt tab / multitask with no drawbacks (drops to composed only while other windows visible on top of osu)

[peppy]

I'd recommend against using such applications as we cannot support your game if you do. We'll be providing D3D and vulkan in the near future, so please wait for that instead.

[mirh]

Can repro this when running my monitor (1920x1080@60) at non-native resolution. Enabling GPU scaling seems to fix it.

This just means that the problem was display scanning then (triggering it is actually far more complex than it seems)
"Longer than expected" is probably just the actual mode switching on the monitor, adding up to the normal short delay for Windows to reshuffle its frontbuffer and the desktop.

I don't know why it happens then (in-game refresh rate being slightly different from the desktop perhaps?) but of course the SK upgrade fixes it, since flip mode would at most allow some glorified borderless fullscreen.

[AeliusSaionji]

flip mode would at most allow some glorified borderless fullscreen.

For the record, this is desirable. Flip mode's latency is equivalent to exclusive fullscreen. There is no upside to using exclusive fullscreen anymore, and plenty of downsides.

Looking forward to the upcoming native flip model support!

[mirh]

Of course.

Though I could also imagine of cases where you would want the full ass mode switch to happen tbh.
I don't know, for instance a system with limited video bandwidth, where you'd rather play at a lower resolution (pixel-wise or color-wise) with a higher refresh rate than your normal desktop one.

[AeliusSaionji]

Fellow CRT enthusiast? 😄

But you don't need exclusive fullscreen to trigger a modeswitch. Osu could just support modeswitching. That's what all dx12 games do, (and that's actually a feature of SK: you can define a preferred mode line per game)

[mirh]

I meant with respect to this issue. Even if you had a flip-something with DXGI_SWAP_CHAIN_FLAG_ALLOW_MODE_SWITCH, you would still need a noticeable amount of time to switch resolution.
(and no, I was more concerned with cheap laptops that only have a shitty HDMI port to connect real monitors)

[peppy]

Please wait for the new renderer to come online, which should resolve this.

[peppy]

Closing as should-be-resolved.