The corner widget on the desktop is squared, while its shadow is a quarter circle. It is best if the shadow is removed and the only shadow left is the one under the button. When on hover, simply brighten.
What Plasma theme are you using? The desktop toolbox does not have a shadow in Breeze, does it?
Is the quarter circle you're thinking of perhaps the hotcorner effect?
Yes! Exactly. When hot corners are enabled, this shadow covers the corner menu button. If your hot corner is the right one, then it covers the close button for a full screen window. Martin mentioned that this appears because of the plasma theme you are using. I tried a few others and the shadow persists. Is there really a need to have them? At this point, I am not sure what other approach is better.
OK, this is drawn by KWin and perhaps themed by Breeze. Are you asking for no hotcorner effect at all, or a more subtle one?
At this point, my recommendation would be to get rid of it. However, in speaking with Martin, he said he wouldn't allow this because it sounded like doing something out of personal desire and would affect too many people negatively. So I don't know what an alternative would be? Maybe instead of a shadow, we use a corner line?
The glow is using the widgets/glowbar.svgz from the Plasma theme. Feel free to play around with that graphic for a different effect.
Maybe we could just make it smaller? FWIW macOS shows no effects for hotcorners.
Smaller? It's tiny here... (Doesn't look like it scales with dpi)
Not sure if related, but my computer also seems to get confused when the cursor gets to the corner. The effect does a little bit of glowing and flickering but the cursor needs to really push to the corner for the effect to activate too. I we have to keep it, then maybe we want to turn it into lines along the border. Like this: |_ _|
> but the cursor needs to really push to the corner for the effect to activate too. That's deliberate based on feedback to avoid accidental triggering.
Unfortunately, that basically kills the usability. You need to push so hard and so deliberately that it's really never any faster to use the hotcorner than alternative user interfaces.
This bug has been fixed with a rewrite in Plasma 5.18 that has removed the Desktop Toolbox in its current form.