`background_opacity` not working in fullscreen under Sway

[josswright]

Describe the bug I am running kitty under sway with background_opacity set to 0.9, and a background defined in sway's config file: via `output "*" bg " fill'.

The opacity setting works perfectly until I make kitty fullscreen, either by keyboard shortcut or by startup options. I originally noticed this when I tried to run kitty with its --start-as fullscreen option.

When I exit fullscreen, then background opacity works as before.

I saw in another issue that there's something strange about how sway sets its background image, so maybe this is related?

To Reproduce Steps to reproduce the behavior:

1. Run kitty, with -o background_opacity=0.8 in sway with a background set, then maximise (either by sway's keyboard shortcut, or kitty's.)
2. (Alternatively) Run kitty --start-as fullscreen -o background_opacity=0.8.

The background of the kitty window will be solid background colour.

Environment details

kitty 0.33.1 created by Kovid Goyal
Linux lovecraft 6.8.2-arch2-1 #1 SMP PREEMPT_DYNAMIC Thu, 28 Mar 2024 17:06:35 +0000 x86_64
Arch Linux 6.8.2-arch2-1 (/dev/tty)

Running under: Wayland
Frozen: False
Paths:
  kitty: /usr/bin/kitty
  base dir: /usr/lib/kitty
  extensions dir: /usr/lib/kitty/kitty
  system shell: /usr/bin/zsh
Loaded config files:
  /home/<user>/.config/kitty/kitty.conf

Config options different from defaults:
allow_remote_control       yes
background_opacity         0.97
bold_font                  Space Mono Pure Bold
bold_italic_font           Space Mono Pure Bold Italic
click_interval             0.5
close_on_child_death       True
confirm_os_window_close    0
copy_on_select             clipboard
cursor_blink_interval      0.5
cursor_shape               3
cursor_stop_blinking_after 0
disable_ligatures          2
enable_audio_bell          False
font_family                Space Mono Pure
font_size                  10.0
initial_window_height      (200, 'px')
initial_window_width       (320, 'px')
input_delay                1
italic_font                Space Mono Pure Italic
macos_option_as_alt        3
mouse_hide_wait            10.0
remember_window_size       False
scrollback_pager           ['less', '+G', '-R']
select_by_word_characters  :@-./_~?&=%+#
shell_integration          frozenset({'no-sudo'})
symbol_map:
    U+0400 - U+04ff → SF Mono
    U+2800 - U+28ff → Fira Code Medium
    U+3040 - U+309f → Sarasa Mono CL
    U+30a0 - U+30ff → Sarasa Mono CL
    U+4e00 - U+9fff → Sarasa Mono CL
    U+ff00 - U+ffef → Sarasa Mono CL
url_style                  1
window_border_width        (1.0, 'pt')
Changed shortcuts:
    kitty_mod+- →  decrease_font_size
    kitty_mod+= →  increase_font_size
    kitty_mod+backspace →  restore_font_size
    kitty_mod+e →  run_simple_kitten text url_hints
    kitty_mod+u →  input_unicode_character
Colors:
    active_border_color        #526270   
    active_tab_background      #171d23   
    active_tab_foreground      #d8e2ec   
    background                 #171d23   
    color0                     #171d23   
    color1                     #d95468   
    color10                    #1d252c   
    color11                    #28323a   
    color12                    #b7c5d3   
    color13                    #f6f6f8   
    color14                    #dd9d82   
    color15                    #fbfbfd   
    color2                     #8bd49c   
    color3                     #ebbf83   
    color4                     #539afc   
    color5                     #b62d65   
    color6                     #70e1e8   
    color7                     #d8e2ec   
    color8                     #526270   
    color9                     #ff9e64   
    cursor                     #d8e2ec   
    foreground                 #d8e2ec   
    inactive_border_color      #1d252c   
    inactive_tab_background    #1d252c   
    inactive_tab_foreground    #b7c5d3   
    selection_background       #d8e2ec   
    selection_foreground       #171d23   
    tab_bar_background         #1d252c   
    url_color                  #b7c5d3   

Important environment variables seen by the kitty process:
    PATH                                <censored>
    LANG                                en_GB.UTF-8
    VISUAL                              /usr/bin/vim
    EDITOR                              /usr/bin/vim
    SHELL                               /usr/bin/zsh
    DISPLAY                             :0
    WAYLAND_DISPLAY                     wayland-1
    USER                                <censored>
    XCURSOR_SIZE                        24
    XDG_SEAT                            seat0
    XDG_SESSION_TYPE                    wayland
    XDG_SESSION_CLASS                   user
    LC_MESSAGES                         
    XDG_VTNR                            1
    XDG_SESSION_ID                      4720
    XDG_RUNTIME_DIR                     /run/user/1000

Additional context (Behavoiur is reproduced with kitty --config NONE -o background_opacity=0.8.)

My terminal theme is set via Tinted Theming both for kitty directly, and for zsh via a base16 shell script, so I don't think that this will be due to an interaction with the background colour as mentioned in comments about background_opacity in kitty's default config file.

[kovidgoyal]

This is a wayland limitation, with their usual security theatre excuse for removing useful functionality.

https://gitlab.freedesktop.org/wayland/wayland-protocols/-/issues/116

[josswright]

Ugh. Thanks for replying! Looks like, as of this comment, it's still being actively debated by people wanting fullscreen transparent terminals, so here's hoping that it can be resolved sensibly.

[josswright]

Just to add, in case anyone else stumbles across this, two potential workarounds for a specific, fullscreen terminal. (I use thits for focused writing.)

Tinted background image: kitty --start-as=fullscreen -o background_tint=0.9 -o background_image_layout=cscaled -o background_image=<path_to_background_png>

Alternatively, switch to an empty workspace and hide the bar, so you get effective fullscreen for that terminal. If you use waybar under sway, you can toggle hiding it with a kill -SIGUSR1:

killall -SIGUSR1 waybar
kitty
killall -SIGUSR1 waybar

Both are just minor hacks with annoyances, so I hope that the fundamental wayland issue will be resolved, but for my usage the second is just about working for now.