Trixie KDE Plasma 6 Wayland Rendering Bug

[The Tall Man]

On the OrangePI-5-Plus, using an edge kernel, I've found that the desktop environment's GPU rendering works very smoothly on Wayland, in KDE 6 on Debian Trixie. It renders much more smoothly than gnome with Wayland (it's been my experience that the edge kernel is the only one that works).

 

But I've encountered a major rendering bug. It only appears in Trixie KDE Plasma 6 with Wayland rendering. It does not appear when using x11 or when using either rendering in gnome. Nor does it appear at all in Bookworm.

 

I have tried all kinds of things to "fix" these to no avail, including installing more wayland and mesa packages, then upgrading them to stable backports and then even to unstable testing (forky) versions. I've also tried the Debian unstable edge kernel from testing (6.16.3) as well as the Armbian stable edge kernel (6.16.4) with the same results.

 

I installed Debian Trixie using the Debian .iso installer (w/ EFI boot), then upgraded to their edge/testing kernel (6.16.3) from their testing/forky repository. The bug showed up in pure Debian without a drop of Armbian. Then I installed the Armbian stable edge kernel (6.16.4) to replace the Debian edge/testing kernel in that installation. The bug remained.

 

The rendering bug also showed up in the release version of Armbian Trixie 25.8.1 using the Armbian edge kernel.

 

KDE 6 Wayland Render Bug Symptom: The [ALT-TAB] Task-Switcher's Text Labels (see screenshot #1)

The major place this bug shows up is in the task switcher (using ALT-TAB). The window labels, instead of rendering as textual fonts, they render as blocks.

 

I tried several things with the fonts, from changing their type and size, turning on/off anti-aliasing, to changing the desktop themes, and so on. I also tried using different "task switchers" from the list. All I got were the same blocks -they just appeared in different sizes and positions with no other changes.

 

So I'm reasonably sure the rendering issue has nothing to do with fonts, desktop themes, Plasma settings, etc.

 

KDE 6 Wayland Render Bug Symptom: glmark2 (x11) verses glmark2-wayland (see screenshots #2 and #3)

Using the command-line utility: glmark2, there's an x11 version and a Wayland version. The each render to an 800x600 window. Normally the only visual difference between them is that the Wayland version has no window borders around it. But with this bug, the Wayland version renders significantly smaller on the screen, and also at a significant performance reduction (>50%).

 

 

Conclusion

I already know it isn't an Armbian issue.

I don't believe it's a kernel issue either.

I'm reasonably sure it has nothing to do with fonts, themes, or Plasma settings.

 

In my internet searches, I have found no other reports of this specific rendering bug that I think are relevant to whatever is happening now.

 

I did find some vague statements about there still being some "issues" with rendering in the upgrade from KDE 5 (using QT5 libraries) to KDE 6 (using QT6 libraries).

 

I also read that KDE Plasma 6 has a somewhat unique interface or relationship with Wayland and uses its own protocols with it. I think this explains why the bug doesn't show up in gnome, and also helps to isolate, to a degree, where the bug actually is.

 

From what I've read, apparently this issue shows up differently on different systems? It is my impression that these specific symptoms of this bug may be  unique to this hardware (Rockchip rk3588 SoC) or GPU (MALI-G610 (built-in)), even though it is a clearly a software bug.

 

Screenshot #1: [ALT-TAB] task-switcher

 

Screenshot #2: glmark

 

Screenshot #3: glmark-wayland

 

Edited 1 hour ago by The Tall Man