Dock renders off-screen on multi-monitor with xrandr scaling transforms

[faux123]

Description

After upgrading from plank-reloaded 0.11.161 to 0.11.164, the dock is positioned completely off-screen and invisible. The dock process runs, but the dock window's Y coordinate is placed far below the actual screen boundary.

Environment

• OS: CachyOS Linux (Arch-based), Cinnamon desktop
• Kernel: 6.19.0-2-cachyos
• plank-reloaded: 0.11.164-1
• GLib: 2.86.3
• GTK+: 3.24.51
• libwnck: 43.3
• GPU: NVIDIA RTX 4090

Monitor Setup (xrandr scaling transforms)

Three monitors using xrandr --scale transforms for fractional scaling:

Monitor	Physical Resolution	Scale	Logical Size	Position
DP-4 (primary)	3840x2160 @ 144Hz	1.6x	6144x3456	0,0
DP-2 (rotated right)	1920x1080 @ 144Hz	2x	2160x3840	6144,0
DP-0	2560x1440 @ 144Hz	2x	5120x2880	8304,505

Total X screen size: 13424 x 3840

Symptoms

The dock window is positioned at y=5724 with height 502, placing it entirely below the screen boundary (total screen height is 3840). The journal shows repeated positioning failures:

[CRITICAL] [DockWindow:290] Retry #3 update_size_and_position() to force requested values!
[CRITICAL] [DockWindow:290] Retry #4 update_size_and_position() to force requested values!
...
[CRITICAL] [DockWindow:290] Retry #11 update_size_and_position() to force requested values!

The _NET_WM_STRUT and _NET_WM_STRUT_PARTIAL are both all zeros.

Root Cause

The struts fix in 0.11.162 (commit e4733a25 — "Fix struts using primary monitor dimensions instead of full screen size") changed positioning to use screen.get_height()/screen.get_width() instead of monitor.get_geometry(). The compute_struts() method multiplies values by the window scale factor (window.get_window().get_scale_factor()).

With xrandr scaling transforms, the X screen dimensions (13424x3840) are already in the scaled coordinate space, but get_scale_factor() returns 2 (GTK detects HiDPI). This double-counts the scaling, producing an off-screen Y position.

Workaround

Setting GDK_SCALE=2 as an environment variable before launching plank makes the dock render at the correct position:

# Without workaround: dock at y=5724 (off-screen)
# With GDK_SCALE=1:   dock at y=3589, height=251 (visible but half-size, not HiDPI)
# With GDK_SCALE=2:   dock at y=3338, height=502 (correct position and HiDPI size)

Previous Version

plank-reloaded 0.11.161 worked correctly with this same monitor configuration.

Related

Possibly related to #140 (maximized windows overlap dock on multi-monitor), which is caused by the same struts calculation change.

[zquestz]

Thanks for the detailed report — your analysis of the coordinate space mismatch was right on.

The root issue was that screen.get_width()/screen.get_height() returns values in different coordinate spaces depending on the GTK3 version and distro — sometimes raw X11 pixels, sometimes GDK logical pixels. The struts calculation mixed these with monitor geometry values (which are always GDK logical), causing the scale factor to be applied incorrectly.

The fix avoids those functions entirely. We now compute the screen bounds by iterating all monitor geometries, which are always in GDK logical pixels. The formula then multiplies everything by the scale factor once to produce the root window coordinates that _NET_WM_STRUT_PARTIAL requires.

We also added a fix for runtime scale factor changes — the dock now repositions itself when the scale factor changes without a resolution change.

Both fixes are in master. Can you test with your 3-monitor xrandr setup and confirm the GDK_SCALE=2 workaround is no longer needed?