swayfx renders zen browser as several regions, creating "stars".

[moshpirit]

• Swayfx Version:

  • swayfx version 0.6 (based on sway 1.12.0)

• GPU / Driver:

  • Intel Alder Lake-P GT2 (Iris Xe Graphics), open-source i915 kernel driver, Mesa (OpenGL renderer string: Mesa Intel(R) Iris(R) Xe Graphics (ADL GT2)). Not using proprietary nvidia drivers.

• Debug Log:

  • Full debug log (sway -d 2> ~/sway.log), ~4400 lines: https://github.com/user-attachments/files/31149690/sway.log
  • Note: this run was launched from within an already-running graphical session (nested Wayland backend), not from a clean TTY. The visual bug reproduces the same way regardless.

• Configuration File:

  • Relevant section (sway-windowrules.conf), with corner_radius set to 5 (also reproduces at higher values, e.g. 10):

    default_border pixel 2
    default_floating_border pixel 2
    hide_edge_borders --i3 smart_no_gaps
    corner_radius 5
    animation_duration_ms 100
    gaps inner 6
    gaps outer 2
    smart_borders on
    smart_gaps on
    

  • Relevant Zen Browser window rules (sway-windowrules.conf):

    assign [app_id="(?i)firefox|zen"] $ws2
    for_window [app_id="(?i)firefox|WebApp-chapi(?i)|(?i)zen"] focus; focus parent; layout tabbed; mark _tabbed; [workspace=__focused__] move to window mark _tabbed; border pixel 0, opacity 1
    

• Stack Trace:

  • N/A — sway does not crash, this is a rendering issue.

• Description:

  When using Zen Browser in SwayFX with corner_radius enabled, gaps shaped like a "four-pointed star" appear in the browser window during sway animations (e.g. when opening the window, moving it, or switching workspaces). The larger the corner_radius value, the bigger these gaps get.

  This same symptom was originally reported in Zen Browser as gaps revealing the desktop wallpaper ("stars"): On wayland, stars show the wallpaper on zen browser. zen-browser/desktop#10529

  After checking with the Wayland project (https://gitlab.freedesktop.org/wayland/wayland/-/work_items/605), I was told the cause is how the compositor applies rounded corners:

  Your compositor applies rounded corners to each region it renders instead of only to the window as a whole.

  In other words, SwayFX appears to apply the corner rounding (corner_radius) to each region/subsurface it renders separately, instead of applying it to the window as a whole. When these regions overlap or get recomposited during an animation, gaps appear where nothing is painted, revealing whatever is behind (the wallpaper or other windows), with a characteristic four-pointed star shape.

  Steps to reproduce:

  1. Configure sway with corner_radius enabled to a reasonable value (e.g. 10-15).
  2. Open Zen Browser.
  3. Trigger an animation (open the window, move it, switch workspace, scroll within the page itself, resize, etc.).
  4. Observe the star-shaped gaps appearing over the Zen Browser window, showing the desktop wallpaper through them.

  Expected behavior: rounded corners should be applied to the window as a whole, without leaving gaps between the different rendered regions/subsurfaces.

  Actual behavior: four-pointed star-shaped gaps appear, whose size scales with the corner_radius value.

Feel free to ask for anything for more information.