Context:
Motif hints [1] allow applications to request specific window manager
frame decorations. Most applications like alacritty, chromium, and
godot, use the hints as a binary flag, setting or un-setting
`MWM_DECOR_ALL`.
Previously [2], we had disallowed applications to set the "normal"
border style through motif hints. This effectively meant that users that
had set `default_border pixel` would not see applications spawning with
normal decorations [3].
However, that meant that applications like godot [4] could not toggle
their border between none and normal so the behaviour changed with
v4.21 [5].
That change however also allowed applications to override the default
none/pixel border style the user set. For example, alacritty can be
configured to either have all or no decorations [6] and they always set
the motif hint on startup, completely overriding i3 user's preference:
1. If decorations are disabled with alacritty's config then they will
override `default_border normal` and no title will be used.
2. If decorations are enabled (also the default behavior) with
alacritty's config then they will override `default_border pixel` and
a title will be used.
This patch redefines how we interpret motif hints. When a client sets
`MWM_DECOR_ALL`, we interpret it as "the maximum decoration the user has
allowed for this window". I.e., if a client was all decorations and the
user expects the window to not have a title, we don't include the title
in "all" decorations.
The user's preference is determined by these:
1. For new tiling windows, as set by `default_border`
2. For new floating windows, as set by `default_floating_border`
3. For all windows that the user runs the `border` command, whatever is
the result of that command for that window.
Example:
- User opens new tiling window with `default_border pixel` => maximum
decoration = PIXEL
- Window requests all/title decorations => i3 enforces the user maximum
decoration, PIXEL (no change)
- Window requests no decorations => i3 accepts it and sets border to
NONE, maximum decoration remains PIXEL
- User toggles the border, next style is NORMAL => maximum decoration is
now NORMAL
- Window requests no decorations => i3 accepts it and sets border to
NONE
- Window requests all/title decorations => i3 accepts it and sets the
maximum border, NORMAL
- User toggles the border, next style is NONE => maximum decoration is
now NONE
- Window requests all/title decorations => i3 enforces the user maximum
decoration, NONE (no change)
With this, we will still allow behaviour where windows can toggle their
border style with motif hints [4][7].
Reference/footnotes:
[1]: https://linux.die.net/man/3/vendorshell
[2]: https://github.com/i3/i3/pull/2386
[3]: Notice how there is apparently a gap because `default border none`
settings would not be respected if an application wanted just "border"
decorations but this was never reported, probably because of the rare
conjunction of applications requesting that and users defaulting to none
borders.
[4]: https://github.com/godotengine/godot/issues/40037
[5]: https://github.com/i3/i3/pull/5135
[6]: Set by an underlying library here:
fafdedfb7d/src/platform_impl/linux/x11/util/hint.rs (L113-L142)
called by alactitty here:
4ddb608563/alacritty/src/display/window.rs (L341)
[7]: https://github.com/i3/i3/issues/3678Closes#3678Fixes#5149
f6097d4a37