komorebi/docs/linux/usage/borders.md

Borders

komorebi puts a colored border around every window. It does not draw it: a KWin effect, KDE Rounded Corners, draws the border outside each window, in the gap between the tiles, and komorebi tells the effect how wide it is, how round the corners are and which color each window's border has. The border around the window that has the focus is blue, and the border around every other window is gray.

Installing the effect

The effect is not part of KWin, and KWin finds effects when it starts: log out and in again after installing it. On NixOS the flake's module installs it with komorebi, which is what services.komorebi.effects.borders.enable does (it is on by default); the effect is built so that KWin does not load it until komorebi asks. installation.md has the module's options.

komorebi loads the effect when it starts and borders are on, and unloads it when it exits or the borders are turned off. A machine that does not have the effect has no borders: komorebi says so once in its log, and leaves no room for them.

Turning borders on and off

komorebic border turns borders on or off. They are on by default.

komorebic border disable
komorebic border enable

Colors

A window's border has the color of what the window is to the layout:

Kind	Window	Default
single	the focused window	blue, 66 165 245
unfocused	every other window	gray, 128 128 128
unfocused-locked	a locked container that does not have the focus	red, 158 8 8
stack	a stack that has the focus	green, 0 165 66
monocle	a monocled window	pink, 255 51 153
floating	a floating window that has the focus	yellow, 245 245 165

komorebic border-colour sets the color of a kind, from its red, green and blue, each from 0 to 255; without --window-kind it sets single.

komorebic border-colour 255 128 0
komorebic border-colour --window-kind unfocused 64 64 64
komorebic border-colour --window-kind floating 200 200 0

The stock KDE Rounded Corners has one color for the active window and one for the others. The build the flake installs also takes a color for each window, which is what lets a locked, a floating, a stack and a monocled window have colors of their own. With the stock effect every kind is drawn as single or unfocused, whichever is closer, and komorebi says so once in its log.

Width and room

komorebic border-width sets how thick the border is, in pixels: 10 by default. The effect draws at most 20 pixels, and draws the border only where a window has a shadow, so a window with no shadow has no border.

While the borders are drawn, the layout leaves room for them: every tile gives up the width of the border on each side, so that the border is drawn in the gap between two windows and does not fall on the window next to it. komorebic border-offset leaves more room than the width, in pixels, which the effect draws nothing in. With borders off, or without the effect, the layout leaves no room at all. A change of the width or the offset reaches the layout the next time the workspace is tiled again, which komorebic retile does.

komorebic border-width 6
komorebic border-offset 2
komorebic retile

In komorebi.json

The same settings can be in komorebi.json: border, border_width and border_offset are what the three commands above set, and border_radius is how round the corners are, in pixels (10 by default), which has no command. The file sets them when the daemon starts and when the file changes; a key it leaves out leaves the setting as it is.

{
  "border": true,
  "border_width": 6,
  "border_offset": 2,
  "border_radius": 12
}

border_colours sets the colors of the kinds of window above, each as red, green and blue or as a hex color, and leaves out the kinds it does not name. A theme, which the theme key of the file gives too, replaces them.

{
  "border_colours": {
    "single": { "r": 255, "g": 128, "b": 0 },
    "unfocused": "#404040"
  }
}

What is put back

The effect keeps its settings in the user's kwinrc, in the group [Round-Corners]. komorebi writes them when it asks for the border, and when it exits or the borders are turned off it puts back what the user had there, also after a crash: the next run puts them back when it stops.