Odd mouse interaction with flow control and links

[edwloef]

Describe the bug
Hovering over hyperlinks in Flow Control leads to the hyperlink underline flickering.

To Reproduce
Steps to reproduce the behavior:

1. Open a file containing hyperlinks in Flow Control.
2. Hover over the hyperlink with the mouse.
3. See error

Environment details

kitty 0.39.1 created by Kovid Goyal
Linux arch 6.13.5-arch1-1 #1 SMP PREEMPT_DYNAMIC Thu, 27 Feb 2025 18:09:44 +0000 x86_64
S{PRETTY_NAME} 6.13.5-arch1-1 (/dev/tty)

DISTRIB_ID="Arch"
DISTRIB_RELEASE="rolling"
DISTRIB_DESCRIPTION="Arch Linux"
Running under: Wayland (sway version 1.10.1) missing: blur
OpenGL: '4.6 (Core Profile) Mesa 24.3.4-arch1.1' Detected version: 4.6
Frozen: False
Fonts:
  medium: CascadiaMonoRoman-Regular: /usr/share/fonts/TTF/CascadiaMono.ttf:262144
          Features: ()
    bold: CascadiaMonoRoman-SemiBold: /usr/share/fonts/TTF/CascadiaMono.ttf:327680
          Features: ()
  italic: CascadiaMono-Italic: /usr/share/fonts/TTF/CascadiaMonoItalic.ttf:262144
          Features: ()
      bi: CascadiaMono-SemiBoldItalic: /usr/share/fonts/TTF/CascadiaMonoItalic.ttf:327680
          Features: ()
Paths:
  kitty: /usr/bin/kitty
  base dir: /usr/lib/kitty
  extensions dir: /usr/lib/kitty/kitty
  system shell: /bin/zsh
System color scheme: dark. Applied color theme type: none
Loaded config files:
  /home/edwin/.config/kitty/kitty.conf

Config options different from defaults:
clipboard_control            ('write-clipboard', 'write-primary', 'read-clipboard', 'read-primary')
close_on_child_death         True
confirm_os_window_close      0
cursor_blink_interval        (0.0, kitty.options.utils.EasingFunction(), kitty.options.utils.EasingFunction())
cursor_shape                 2
cursor_shape_unfocused       2
enable_audio_bell            False
font_family                  Cascadia Mono
placement_strategy           top-left
scrollback_indicator_opacity 0
scrollback_lines             9999
Added shortcuts:
	alt+0 →  goto_tab 10
	alt+1 →  goto_tab 1
	alt+2 →  goto_tab 2
	alt+3 →  goto_tab 3
	alt+4 →  goto_tab 4
	alt+5 →  goto_tab 5
	alt+6 →  goto_tab 6
	alt+7 →  goto_tab 7
	alt+8 →  goto_tab 8
	alt+9 →  goto_tab 9
Changed shortcuts:
	kitty_mod+f →  no-op
	kitty_mod+left →  no-op
	kitty_mod+p > f →  no-op, kitten hints --type hyperlink, kitten hints --type linenum, kitten hints --type hash --program -, kitten hints --type word --program -, kitten hints --type line --program -, kitten hints --type path, kitten hints --type path --program -
	kitty_mod+right →  no-op
Colors:
	active_tab_background        #ebdbb2   
	background                   #282828   
	color0                       #282828   
	color1                       #cc241d   
	color10                      #b8bb26   
	color11                      #fabd2f   
	color12                      #83a598   
	color13                      #d3869b   
	color14                      #8ec07c   
	color15                      #ebdbb2   
	color2                       #98971a   
	color3                       #d79921   
	color4                       #458588   
	color5                       #b16286   
	color6                       #689d6a   
	color7                       #a89984   
	color8                       #928374   
	color9                       #fb4934   
	cursor                       #ebdbb2   
	foreground                   #ebdbb2   
	inactive_tab_background      #928374   
	selection_background         #ebdbb2   
	selection_foreground         #282828   

Important environment variables seen by the kitty process:
	PATH                                /usr/local/sbin:/usr/local/bin:/usr/bin:/usr/lib/jvm/default/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl:/usr/lib/rustup/bin:/home/edwin/.cargo/bin
	LANG                                en_US.UTF-8
	EDITOR                              flow
	SHELL                               /bin/zsh
	DISPLAY                             :0
	WAYLAND_DISPLAY                     wayland-1
	USER                                edwin
	XCURSOR_SIZE                        24
	XDG_SEAT                            seat0
	XDG_SESSION_TYPE                    wayland
	XDG_SESSION_CLASS                   user
	XDG_VTNR                            1
	XDG_SESSION_ID                      1
	XDG_RUNTIME_DIR                     /run/user/1000

Additional context
The problem persists with kitty --config NONE and an empty Flow Control config. This may be related to Flow Control processing mouse reports even when no button is clicked.

Flow Control issue: neurocyte/flow#198

[kovidgoyal]

Run kitty with --dump-bytes, do the minimum required to reproduce the
issue and post the dump. Do it in a kitty window of 80x25 cells, you can
create such a window with

kitty --dump-bytes /tmp/dump.bin -o remember_window_size=n -o initial_window_width=80c -o initial_window_height=25c

assuming you aren't using a tiling window manager, if you are then you
will also need to make the window float.

[edwloef]

dump.bin.zip

[kovidgoyal]

Well that dump tells us why its happening, basically when the mouse moves, flow sends a synchronized screen update containing no actual new rendering, you can see this in action
by running

kitty --dump-commands flow test.txt

where test.txt contains a URL, when moving the mouse over the URL flow generates the following commands repeated for every pixel of mouse movement:

screen_set_mode 2026 1
screen_reset_mode 25 1
screen_cursor_position 1 1
select_graphic_rendition 0
screen_cursor_position 2 6
screen_set_mode 25 1
screen_reset_mode 2026 1

All that does is start a synchronized update of the screen, hide the cursor, move the cursor to top left, reset all cursor text styling attributes, move the cursor back to where it was and show the cursor again, the finally end synchronized update. This whole sequence does nothing at all, other that reset text styling attributes on the cursor.

The flickering happens because of a kitty limitation with synchronized screen updates where when one is started, hovered underlines are hidden because kitty assumes that some changes on the screen will happen so it doesnt bother to track the underline. Then once the synchronized update is committed, kitty again tracks the underline and re-shows it. Causing the flicker.

Ideally, flow shouldn't be doing this its just wasted processing for no effect. And at some point I will have to implement tracking of underlines during a synchronized update in kitty since if flow has this behavior am sure eventually more applications will start having it as well.