The wallpaper gets scaled down after restart, and does not fit the bigger resolution monitor

[JanisE]

 * Cinnamon version: 3.4.6
 * Distribution: Mint 18.2
 * 64 bit
 * inxi -G
Graphics:  Card: Intel Sky Lake Integrated Graphics
           Display Server: X.Org 1.18.4 drivers: intel (unloaded: fbdev,vesa)
           Resolution: 1366x768@60.00hz, 1920x1080@60.00hz
           GLX Renderer: Mesa DRI Intel HD Graphics 520 (Skylake GT2) GLX Version: 3.0 Mesa 17.0.7

Issue

The wallpaper gets scaled down after restart, and does not fit the (secondary) bigger resolution monitor.

Steps to reproduce

• Set a 2560x1600 px image as a centered desktop wallpaper. It covers all the screen area for both 1366x768 px and 1920x1080 px screens.
• Restart the computer.
• The wallpaper seems to be scaled down to 1366x768 px resolution and covers the smaller (primary) monitor all right, but on the larger resolution monitor the image is smaller now and does not cover all the screen, there are black margins.

Expected behaviour

• The wallpaper is displayed the same way after restarting the computer as it was right after I set it up.

Other information
After restart, if I go to wallpaper settings and click on another image and right back to the original one, the wallpapers are once again set up properly.

[offa]

Since Cinnamon v3.8 I have the same problem on Manjaro (Kernel 4.16, Cinnamon v3.8.2 at the moment). The Wallpaper is scaled on each Login.

Is there any workaround at least?

[offa]

This bug still exists in Cinnamon 4.0.0.

[offa]

Workaround: Adding this script to autostart #5234 (comment)

[BrunoNZ]

I've made some tests on this matter and i found out that swapping .cache/wallpaper filenames kinda works too, because only the file starting with "0_" is used for both monitors. Also, after changing aspect ratio the wallpaper are displayed correctly on both monitors.

Apparently this bug only affects Intel and NVidia machines, but is it possible that the bug is actually on cinnamon's src? If yes, i'm willing to tackle this bug as my first contribution to this project. No promesses, but i'll try!

[offa]

Apparently this bug only affects Intel and NVidia machines,

I can reproduce it on AMD too.

[BrunoNZ]

That's interesting. I talked to some people in IRC chat about it and for what I've heard there are no known cases of AMD machines with this bug.

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If this issue is still relevant:

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[Jazzhoo]

I can confirm that the bug is still here on Mint Cinnamon 22.3. I had it both on Intel Meteor Lake CPU and currently on AMD Ryzen 8845HS.

I'm pretty sure that the issue is related to external monitor of different ratio than the Primary one. i.e laptop is 16:10 and external monitor is 16:9. (1920x1200 and 2560x1440)

In my case the wallpaper fits the whole screen but it's noticeably blurry. Changing wallpaper back and forth seem to fix the issue. However, that's annoying.

[nfsp-ta]

I can also confirm the behavior exactly as @Jazzhoo described.
My laptop has a 1920x1080 integrated display, but docked it's running 3x 1080 monitors spanned horizontally for a resolution of 5760x1080. My desktop wallpaper is set to spanned aspect and I'm using a 5568x1080 image.
If I set the wallpaper while docked, it's clear. But if I take it off the dock, run on its own single display, and then plug it back into the dock, the wallpaper image is blurry. It looks like it is taking the scaled down image from the single display and scaling it back up to the original resolution.
Note that restarting Cinnamon (Alt-F2) does not fix the blurry image, only changing the wallpaper and setting it back again corrects the issue. Also, it only seems to impact the desktop wallpaper, everything else is clear.
Here's two screenshots to show the blurring (zoom to 1:1)

OS: Linux Mint 22.3 x86_64 
Host: Precision 7530 
Kernel: 6.8.0-124-generic 
Shell: bash 5.2.21 
Resolution: 1920x1080, 1920x1080, 1920x1080 
DE: Cinnamon 6.6.7 
WM: Mutter (Muffin) 
WM Theme: Mint-Y-Dark-Blue (Mint-Y) 
Theme: Mint-Y-Dark-Blue [GTK2/3] 
Icons: Mint-Y-Navy [GTK2/3] 
Terminal: gnome-terminal 
CPU: Intel i7-8850H (12) @ 4.300GHz 
GPU: NVIDIA Quadro P1000 Mobile 
Memory: 26185MiB / 48002MiB