Those of you upgrading to Plasma 6.4.1 (released yesterday) may notice a more substantive change than the type we typically make in bug-fix releases: The “highlight window” effect for Task Manager thumbnails is now off by default. This is the effect that makes other windows fade out when you hover over a window’s thumbnail.
Why did we turn it off? Because we discovered that with certain window arrangements and mouse movements, the current implementation could potentially cause full-screen flickering at greater than 3 Hz, which is potentially capable of triggering seizures in sensitive people.
Now, this is very unlikely. You’d need to open multiple full-screen windows of the same app, hover over their task to show thumbnails for them, move the pointer over one of the thumbnails, and then move it rapidly across all the others.
…Unlikely, but not impossible! And until and unless we can fix the effect to not be so flickery with this specific usage, it’s safer to keep it off. Furthermore, even for people who aren’t photosensitive, it’s currently a really unpleasant visual effect.
This work was done as a part of KDE’s recent accessibility push, and specifically the focused effort to make Plasma fully compliant with new EU accessibility regulations. Work is currently going on at all levels of the software stack, with multiple people involved and multiple sponsors funding it — both KDE e.V. itself, and also outside firms and institutions. If you’d like to see more of this kind of thing, donating to KDE e.V. is always a great idea, as it allows KDE e.V. itself to support an even larger amount and proportion of it.
There seems to be a bit of a doom-and-gloom vibe about accessibility in our community lately, but hopefully it’s clear that not only does KDE care, but it puts its money where its mouth is on this topic! Maybe we’re not 100% there yet, but we’re pointed in the right direction and motivated to continue accelerating towards it.
Adventures in Linux and KDE 
Seems like the pragmatic choice to me, much rather avoid incidents like that completely rather than banking on that specific group never encountering the bug.
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With thee default settings, there is no ‘flicker’ to be pedantic. It changes the screen at the same speed of pointer movement from one thumbnail to another. This can be fast enough to cause issue. The animation curve can be twicked, or a delay can be added if the effect is triggered once (first highlight). I’m not familiar with this effect impl though so likely I’m writing nonsense lol.
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The problem specifically is that the animation is cancelled when it goes from fading away (no windows being highlighted) to fading back in (windows being highlighted). This results in a jump rather than a smooth transition, which is the problem here.
This isn’t triggered by alt+tab because there’s no way to rapidly highlight nothing and then something again but because of the empty space between the thumbnails in the Task Switcher tooltip, it’s surprisingly easy to rapidly trigger just by moving your mouse across them at a reasonable speed.
I think the fix will be a combination of making the animation slower (150ms -> 250ms, too much and it no longer feels responsive) and of course fixing the issue which causes the animation to cancel.
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I’d like to think that the doom-and-gloom vibe about accessibility is actually a good thing because it shows that our community is starting to care a lot more about accessibility, and as a result is starting to uncover all the issues with it which were previously ignored. Now that it’s getting more attention, there’s a bigger chance that we can improve it.
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