XnViewMP (Linux) is much slower on Wayland than X11

[winnylinny]

Navigating through images is much slower and laggier on Wayland than X11. Using XnViewMP on X11 is instant and fast without any problems. When I switch to Wayland, it's much slower. I can still "use" the application, but it's more frustrating. Panning a zoomed image is also obviously slower too.

I am on KDE Plasma 6.6.5.

I have tried XnViewMP 1.11.5 and older versions. The behavior is the same. Navigating images is fast and smooth with X11, but sluggish with Wayland. It doesn't matter that the files are on a fast local NVMe.

I have tried the following variables which don't help too much.
QT_QPA_PLATFORM=xcb
QT_SELECT=qt6

I have tried the qt6 beta of XnViewMP.

I have tried the "system-libs" version.

The only solution is to switch back to X11. This is a problem because soon KDE will no longer support X11 as everyone is being forced to use Wayland.

What else can I try?

[xnview]

qt6 beta has same problems? which Linux?

[winnylinny]

qt6 beta has same problems? which Linux?

Yes. I tried qt6 beta from here: viewtopic.php?t=50710

This happens on 2 PC's. Arch Linux and Manjaro Linux. This happens on Nvidia GPU and Intel GPU.

XnViewMP on an old slow laptop with Intel GPU on X11 is faster than a new PC with Nvidia GPU on Wayland. There is an obvious difference in performance. It doesn't only affect navigating images with the mouse wheel and arrow keys, but also affects performance when panning an image that is zoomed.

I will try any advice you have so that XnviewMP is fast and smooth on Wayland like it is with X11.

[xnview]

even with clean xnview.ini? so slower when navigating images in viewer mode? display scaling?

[winnylinny]

Yes. Same issue with clean xnview.ini.

If my Display Scaling is set to 100%, then panning zoomed images is not as slow. It's usable. Slower than X11, but not too bad. Scrolling through images is still very sluggish.

If my Display Scaling is set to 125%, then everything is slow, including panning zoomed images.

If I'm using X11, everything is faster. It doesn't matter if I'm using 100% or 125% scaling. It doesn't matter if I'm using "none" or "bicubic" for zoom.

I might be able to do a screen recording. The problem with that is XnViewMP is using higher CPU under Wayland, which might ruin the video capture.

[xnview]

Yes. Same issue with clean xnview.ini.

panning is the only slow feature??

[winnylinny]

panning is the only slow feature??

Both.

Panning when zoomed.

Navigating through images with arrows or mouse wheel.

[winnylinny]

Some more info.

The slow panning on a zoomed image only happens if the window is maximized or full screen.

[xnview]

The slow panning on a zoomed image only happens if the window is maximized or full screen.

only? display scaling? which resolution?

[winnylinny]

Pierre, I'm doing more tests and it seems that multiple factors are causing XnViewMP to be slower and use more CPU. It's possible that factors combine to create different amounts of slowdown.

I've already made certain that using "bilinear" is much slower than "bicubic". This is funny to me because bilinear is a simpler algorithm.

I can replicate 100% the issue of panning on a zoomed image happens only on maximized window or full screen. If I resize the window to be smaller than full screen, panning is fast and smooth.

I'll report with more tests later when I am free. I will include scaling, resolution, and other variables.

[winnylinny]

I will have to use X11 as long as I can.

Wayland has too many problems and this issue with XnViewMP makes using the application unbearable.

Wayland is such a disappointment that seems to be justified for technical reasons over QoL.

[xnview]

Wayland has too many problems and this issue with XnViewMP makes using the application unbearable.

With display scaling of 100%, you reproduce always in fullscreen/maximized window the slow panning, right? only panning?

[winnylinny]

With display scaling of 100%, you reproduce always in fullscreen/maximized window the slow panning, right? only panning?

This is what I am experiencing with Viewer.

Under X11 with desktop at 100% scaling:

• Very fast navigation and scrolling through images.
• Very smooth panning when zoomed on image with a normal window.
• Very smooth panning when zoomed on image with a maximized or full screen window.

Under X11 with desktop at 125% scaling:

• Very fast navigation and scrolling through images.
• Very smooth panning when zoomed on image with a normal window.
• Very smooth panning when zoomed on image with a maximized or full screen window.

Under Wayland with desktop at 100% scaling:

• Terribly slow navigation and scrolling through images.
• Very smooth panning when zoomed on image with a normal window.
• Passable panning when zoomed on image with a maximized or full screen window.

Under Wayland with desktop at 125% scaling:

• Terribly slow navigation and scrolling through images.
• Very smooth panning when zoomed on image with a normal window.
• Slower panning when zoomed on image with a maximized or full screen window.

I need to switch to X11 in order to use XnViewMP Viewer when navigating and scrolling through images.

[xnview]

Under Wayland with desktop at 100% scaling:

• Terribly slow navigation and scrolling through images.
• Very smooth panning when zoomed on image with a normal window.
• Passable panning when zoomed on image with a maximized or full screen window.

Under Wayland with desktop at 125% scaling:

• Terribly slow navigation and scrolling through images.
• Very smooth panning when zoomed on image with a normal window.
• Slower panning when zoomed on image with a maximized or full screen window.

on a clean Manjaro 26 with KDE Plasma 6.7.4, and XnView MP 1.11.5, i don't see issue when navigating (left/right arrows) between images in viewer, with a clean .ini
Is it possible to have a screencast in Wayland/X11 when you navigate between images?