Linux/X11 HiDPI: full-screen recording overlay is ~2x too large at 200% scale

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
38/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Active
Tech stack
linux, rust, tauri
Domain
desktop, operating-systems

Research direction

Reproduce the full-screen recording overlay on Linux Mint 22.3 with MATE/X11, Xft.dpi=192, and 200% scaling, then trace the overlay's display-size calculation and toolkit entry point. Compare its bounds with the selected display and the GDK_SCALE=1 workaround; done means the overlay covers exactly the display at 200% without shrinking or making the main window unusable.

Written by the indexing model from the issue text.

Description

bug

Version / environment

  • Cap 0.6.0 (.deb, amd64)
  • Linux Mint 22.3, MATE 1.26.2, X11 session
  • Display: eDP-1 2560x1600 (344x215 mm), Intel Arrow Lake graphics (Vulkan, per the Cap log)
  • Xft.dpi = 192; MATE window-scaling-factor = 0 (auto)

What happens
When I choose "record full screen", the blue selection/overlay is about 2x larger than the screen. Cap's main window renders at a normal, readable size.

Workarounds tried

  • Lowering the global desktop scaling makes the overlay correct, but shrinks all UI text on the system, so it isn't practical.
  • Launching with GDK_SCALE=1 (from a terminal): the overlay is correct, but Cap's main window becomes very small and can't be resized.
  • GDK_SCALE=1 GDK_DPI_SCALE=2: overlay still correct, but the window stays small with huge text; buttons unreachable.
  • WINIT_X11_SCALE_FACTOR=1: no visible change (overlay still 2x).
  • Ctrl+ / Ctrl+scroll in the main window: no effect.
  • Settings > Experimental (GPUI preview) does not exist in my build.

Notes

  • The terminal log shows no error or scale-related message at startup. Only unrelated JACK/ALSA and mjpeg warnings.
  • I have not verified whether the overlay window is sized in physical vs. logical pixels, or whether the window toolkit is GTK/WebKit or something else.

Expected
Overlay covers exactly the selected display at 200% desktop scaling, without needing GDK_SCALE=1.

Dominant language
Rust
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