Bug 303437

Summary:	Constant frame rate in Present Windows needed
Product:	[Plasma] kwin	Reporter:	Szczepan Hołyszewski <rulatir>
Component:	effects-present-windows	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED FIXED
Severity:	wishlist	CC:	nate
Priority:	NOR
Version First Reported In:	4.8.4
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed In:	5.23
Sentry Crash Report:

Description Szczepan Hołyszewski 2012-07-12 20:03:23 UTC

The "show all windows" effect in KWin has this feature where the window miniature under the mouse is slightly enlarged, and additionally the other miniatures are grayed out. The transitions are animated, and the problem arises when the system cannot provide enough CPU cycles to make the animation smooth.

When the frame rate drops into the 7-15 Hz range, the steps of changing brightness can be easily perceived. Such a staircase signal is basically the sum of a straight slope and a periodic sawtooth pulse. Worse yet, another window miniature is being faded *out* at the same time, sending apparent brightness pulses *with the opposite sign* to an adjacent area of the user's visual cortex. This is probably more than enough to trigger a seizure in a susceptible individual.

(In fact I might just have had a mild seizure because of this. I'm not a doctor so all I know is that while highlighting windows in the "show all windows" view, I suddenly got this intense feeling of something weird happening to me, heart thumping and all, and I had to turn my eyes away and take a few deep breaths before I could look at the screen again. I'm writing this to present evidence that the health risk is probably real).

Reproducible: Sometimes

Steps to Reproduce:
1. Run in 1600x1200 on an old video card
2. Use the "show all windows" effect (the one started by moving the mouse into the top left corner)

Actual Results:
Window miniatures pulse badly when fading in/out.

Expected Results:
I suggest automatically disabling the fade-out effect if the frame rate cannot be reliably maintained above a certain threshold (ask a neurologist for the exact value).

Comment 1 Martin Flöser 2012-07-12 20:14:49 UTC

thanks for your very important feedback. I'm sorry that you had such a bad experience with this effect.

Our aim is to get all effects to run always smooth even on low end hardware with large screens. We are constantly improving the source base with the aim to deliver a constant 60 fps. The proper approach for our animations is to get them smooth which benefits all users and is in fact easier than detecting a frame rate drop with an adjustment of the runtime behavior of the effect.

We plan to rework this specific effect for 4.10 (see #295775)

Comment 2 Thomas Lübking 2012-07-12 20:27:07 UTC

@Szczepan
Set the animation speed to "instant" which will disable all (most) animations (run "kcmshell4 kwincompositing", it's on the first page)

Do *never* enable the "Show Paint" effect!

Out of curiosity: what is "an old video card"?

Comment 3 Szczepan Hołyszewski 2012-07-12 20:57:55 UTC

Thanks for the animation speed tip Thomas!

While we are at it, I'd like to argue for making the graying-out of the thumbnails in Present Windows optional. See #303438.

"Old video card" is GeForce FX 5200.

Comment 4 Szczepan Hołyszewski 2012-07-12 21:01:37 UTC

> "Old video card" is GeForce FX 5200.

... using current proprietary NVIDIA drivers (ArchLinux package).

Comment 5 Nate Graham 2021-08-19 15:14:43 UTC

This is fixed in the QML rewrite for Plasma 5.23 which is lighter weight. The recent work to boost smoothness in general has also helped.