tiling window managers are wonderful. ultra-flexible text editors are also wonderful. for a spell, i thought i'd found the ideal solution in would have been, save for the fact that i use ordinary, graphical windows as much, if not more than, text buffers, and sometimes those windows are from dodgy programs (e.g., steam) that have trouble with EXWM's fancy input methods.
but i still like emacs a lot. hell, it switches light and dark mode on my machine (still)! so, inspired by such posts as (\sqrt{-1})'s, i set out to get a common set of keybindings between emacs and i3, along with some sane defaults around opening terminals, splitting windows, etc.
i first tried a script with xdotool
and emacsclient
, as in the above-referenced
article, and that worked… but proved to be too slow: i saw lags of up to a
second
timing the script gave a latency of 30 to 100 ms from invocation to exit,
which is still pretty slow but not a dealbreaker. i still don't know where the
rest of the latency came from.
between sending input to emacs and it actually registering. i don't know
if this is because of my emacs version, other packages, emacsclient
weirdness, whatever, but that wasn't going to cut it. plus, it seems wasteful to launch a whole shell-plus just to register a keypress, especially for some of the most commonly pressed key combinations i use. so i did the only rational thing: i patched i3.
my objective was: instead of unilaterally handling commands bound via i3's
bindsym
, add an option to check the currently focused window to see if it's
emacs, and if it is, pass the keypress event through to it.
note that this feature has been requested in the past, and the i3
maintainers have deemed it to be out of scope. i would make this a more
fully-fledged patch if that were not the case.
if emacs
decides "no, i3 should actually handle this," it can use i3-msg
to route the action back.
i succeeded in that, though it might not be the most elegant thing in the world. if you know about web@khz.ac.
relevant i3 code #
i3 uses xcb_grab_key()
with owner_events = 0
on the root src/bindings.c
looks like all unpatched code snippets refer to i3 4.25.1, if you want to follow along.
172struct Binding_Keycode *binding_keycode;
173TAILQ_FOREACH(binding_keycode, &(bind->keycodes_head), keycodes) {
174 const int keycode = binding_keycode->keycode;
175 const int mods = (binding_keycode->modifiers & 0xFFFF);
176 DLOG("Binding %p Grabbing keycode %d with mods %d\n", bind, keycode, mods);
177 xcb_grab_key(conn, 0, root, mods, keycode, XCB_GRAB_MODE_ASYNC,
178 XCB_GRAB_MODE_ASYNC);
179}
this code isn't super relevant, except that i3 entirely steals its bindings from
anyone else by intercepting on the root window. if you're thinking that setting
owner_events = 1
to allow event passthrough so we don't have to re-emit… that would be great, but that appears to instruct only the root window. which is not what we want.
in i3's handle_event()
in src/handlers.c
, if it gets an
1481switch (type) {
1482case XCB_KEY_PRESS:
1483case XCB_KEY_RELEASE:
1484 handle_key_press((xcb_key_press_event_t *)event);
1485 break;
1486 // ...
1487}
handle_key_press()
(src/key_press.c
) looks like this — it receives a keypress event, looks up a binding based on that event, and, if it finds one, runs the associated command: yes, i do know one of the lines is too long. i opted to leave it that way, as that's how it is in the i3 source. i should note, though: i3 has really nice source code! i found it very readable and pleasant to work inside.
12/*
13 * There was a KeyPress or KeyRelease (both events have the same fields). We
14 * compare this key code with our bindings table and pass the bound action to
15 * parse_command().
16 *
17 */
18void handle_key_press(xcb_key_press_event_t *event) {
19 const bool key_release = (event->response_type == XCB_KEY_RELEASE);
20
21 last_timestamp = event->time;
22
23 DLOG("%s %d, state raw = 0x%x\n", (key_release ? "KeyRelease" : "KeyPress"), event->detail, event->state);
24
25 Binding *bind = get_binding_from_xcb_event((xcb_generic_event_t *)event);
26
27 /* if we couldn't find a binding, we are done */
28 if (bind == NULL) {
29 return;
30 }
31
32 CommandResult *result = run_binding(bind, NULL);
33 command_result_free(result);
34}
notably, this function receives the original xcb_key_press_event_t
from xcb_send_event()
. unfortunately, the window receiving the event will still lose focus, as i3 is intercepting key events globally. i haven't fixed this; let me know if you know how.
this looks like a reasonable place to make a change!
the patch #
Binding
struct changes
i decided to modify Binding
(include/data.h
) with an extra field to indicate a class of window which should, for that binding, receive events directly:
/**
* Holds a keybinding, consisting of a keycode combined with modifiers and the
* command which is executed as soon as the key is pressed (see
* src/config_parser.c)
*
*/
struct Binding {
// ...
/** Window class to use for key passthrough. Currently an exact string match. */
struct {
char *class;
} passthrough;
};
i also modified the binding initialization to set up passthrough, if provided: there is, of course, associated cleanup code, which i've omitted for brevity. look at the patch file (linked at the end) if you want to see it.
/*
* Adds a binding from config parameters given as strings and returns a
* pointer to the binding structure. Returns NULL if the input code could not
* be parsed.
*
*/
Binding *configure_binding(const char *bindtype, const char *modifiers, const char *input_code,
const char *release, const char *border, const char *whole_window,
const char *exclude_titlebar, const char *command, const char *modename,
bool pango_markup, const char *passthrough) {
// ...
// XXX: should change this to be configurable, but I only care about Emacs, so.
if (passthrough) {
new_binding->passthrough.class = sstrdup("Emacs");
} else {
new_binding->passthrough.class = NULL;
}
return new_binding;
}
handle_key_press()
now has to look at that setting and decide whether to pass
the key event through. if bind->passthrough.class
is set for that binding, we get the currently focused window, check its class, and if that class matches, we re-send the key event to that focused window with interception disabled (else it would just go straight back to i3):
void handle_key_press(xcb_key_press_event_t *event) {
// ...
DLOG("PATCH: checking if we should pass keypress through\n");
if (bind->passthrough.class) {
xcb_generic_error_t *focus_error;
xcb_get_input_focus_reply_t *input_focus = xcb_get_input_focus_reply(
conn, xcb_get_input_focus(conn), &focus_error);
if (focus_error != NULL) {
DLOG("PATCH: could not get focused window");
free(focus_error);
} else {
Con *con = con_by_window_id(input_focus->focus);
const xcb_window_t focus = input_focus->focus;
free(input_focus);
const bool should_pass =
con && con->window->class_class &&
strcmp(con->window->class_class, bind->passthrough.class) == 0;
if (should_pass) {
DLOG("PATCH: forwarding keypress (%d %s %s @ %d %d)\n", focus,
con->name, con->window->class_class, event->event_x,
event->event_y);
event->event = focus;
xcb_send_event(conn, false, focus, XCB_EVENT_MASK_NO_EVENT,
(const char *)event);
return;
}
}
}
DLOG("PATCH: handling keypress normally\n");
CommandResult *result = run_binding(bind, NULL);
command_result_free(result);
}
modifying the parser
i3 includes a parser generator, which reads what appears to be an i3-specific me to do it, email me.
the parser configuration for bindsym
/ bindcode
(parser-specs/config.spec
), after modification, looks like this:
state BINDING:
passthrough = '--passthrough'
->
key = word
-> BINDCOMMAND
state BINDCOMMAND:
passthrough = '--passthrough'
->
command = string
-> call cfg_binding(..., $passthrough, $command)
this section of the parser config defines two parser states: BINDING
(parsing a
bindsym
command, but we haven't parsed a keysym yet) and BINDCOMMAND
(the same,
but after we've parsed the keysym).
the right way to do this, should i have
wanted to have syntax like --passthrough "Emacs"
, would be to move to a new
parsing state upon encountering this flag and eating the next token as
passthrough
. perhaps someday.
i3's parsing variable = <stuff>
and passing that variable to a call
command as a char*
— non-null if encountered and null if not. hence, if the flag --passthrough
appears while parsing, $passthrough
evaluates to the string "--passthrough"
rather than NULL
. then if (passthrough) { /* ... */ }
gets evaluated in
configure_binding()
, and the rest is history.
the emacs side #
now that key passthrough works, all we need is a bit of elisp and life is good. a lot of this is heavily pulled from the (\sqrt{-1}) post linked above. basically, i want to integrate two actions: window movement and opening terminals.
window movement
to start, we need a way for emacs to send messages back to i3 if we try to move beyond an existing window:
(defmacro nausicaa/i3-msg (&rest args)
"Call i3-msg with ARGS."
`(start-process "emacs-to-i3" nil "i3-msg" ,@args))
when either moving windows or moving between windows, emacs should attempt to select one of its own windows in the given direction. failing that, it should instruct i3 to do so:
(defun nausicaa/emacs-i3-windmove (dir)
"Select window in DIR, if it exists; if not, i3-select it."
(let ((other-window (nausicaa/find-other-window dir)))
(if (or (null other-window) (window-minibuffer-p other-window))
(nausicaa/i3-msg "focus" (symbol-name dir))
(nausicaa/do-window-select dir))))
(defun nausicaa/emacs-i3-move-window (dir)
"Do some stuff to move window in DIR.
I should check out `evil-move-window' at some point."
(let ((other-window (windmove-find-other-window dir)))
(cond
((and other-window (not (window-minibuffer-p other-window)))
(window-swap-states (selected-window) other-window))
(t (nausicaa/i3-msg "move" (symbol-name dir))))))
nausicaa/find-other-window
is a function that really just invokes the appropriate windmove command. i wrote it because my existing windmove commands have advice around them (placed there by doom, i expect) that allows them to select popup windows and the minibuffer, which i wanted to reuse:
(defun nausicaa/find-other-window (&rest args)
"Pass ARGS through to `windmove-find-other-window'.
Exists solely so I can reuse `+popup--ignore-window-parameters-a'."
(apply #'windmove-find-other-window args))
(defun nausicaa/do-window-select (&rest args)
"Pass ARGS through to `windmove-do-window-select'.
Exists solely so I can reuse `+popup--ignore-window-parameters-a'."
(apply #'windmove-do-window-select args))
(advice-add 'nausicaa/find-other-window
:around #'+popup--ignore-window-parameters-a)
(advice-add 'nausicaa/do-window-select
:around #'+popup--ignore-window-parameters-a)
arguably the right way to do this is to add that advice to
windmove-find-other-window
, which i might do at some point.
terminals
i am always launching terminals —
sometimes
fifty
a
day.
i typically use mistty as a terminal, since it has delightful integration with the rest of emacs, but it tends to choke on more difficult text rendering tasks, for which alacritty is better suited. at any given moment, in any given directory, i might want to launch either of them, so i wrote a few scripts to invoke either mistty or alacritty from either emacs or i3.
i3 is configured to launch both mistty and alacritty, depending on context, using two scripts:
bindsym --passthrough $super+Return exec mistty-create
bindsym --passthrough $super+Control+Return exec alacritty-create
if those keys pass through to emacs, emacs either launches a mistty session or just shells out to the script:
(defun nausicaa/launch-alacritty ()
(interactive)
(async-start-process "alacritty-create" "bash" nil "-c" "exec alacritty-create"))
(map!
"s-<return>" #'mistty-create
"C-s-<return>" #'nausicaa/launch-alacritty)
mistty-create
is a shell script that tells emacs to open a new frame with mistty in it:
pkgs.writeShellApplication {
name = "mistty-create";
text = ''
${config.programs.emacs.package}/bin/emacsclient -e "(progn (other-frame-prefix) (mistty-create))"
'';
}
alacritty-create
instructs the current alacritty process to create a new window in the current working directory:
pkgs.writeShellApplication {
name = "alacritty-create";
text = ''
if ! ${pkgs.alacritty}/bin/alacritty msg create-window --working-directory "$PWD"; then
env -u INSIDE_EMACS ${pkgs.alacritty}/bin/alacritty "$@" >/dev/null 2>&1 &
disown %env
fi
'';
}
this script has the wonderful property that, if invoked inside emacs, you get an alacritty window in whatever project directory you're currently in, yielding roughly equally ergonomic behavior between mistty and alacritty. it's great.
results #
i3 and emacs play really nicely together now. if you want the patch for i3, it's here. i'll eventually post my full configuration with keycodes, but the above should be enough to get something working.
and if you're like me, and want to do i3 development on nix, here's what i used
for a shell.nix
:
{ pkgs ? import <nixpkgs> { } }:
pkgs.mkShell {
nativeBuildInputs = with pkgs; [
pkg-config
makeWrapper
meson
ninja
installShellFiles
perl
asciidoc
xmlto
docbook_xml_dtd_45
docbook_xsl
findXMLCatalogs
];
buildInputs = with pkgs.buildPackages; [
libxcb
libxcb-util
libxcb-wm
libxcb-keysyms
libxkbcommon
xcbutilxrm
libstartup_notification
libx11
pcre2
libev
yajl
xcb-util-cursor
perl
pango
perlPackages.AnyEventI3
perlPackages.X11XCB
perlPackages.IPCRun
perlPackages.ExtUtilsPkgConfig
perlPackages.InlineC
];
}