3 Michael Stapelberg <michael@i3wm.org>
6 This document is intended to be the first thing you read before looking and/or
7 touching i3’s source code. It should contain all important information to help
8 you understand why things are like they are. If it does not mention something
9 you find necessary, please do not hesitate to contact me.
13 A window manager is not necessarily needed to run X, but it is usually used in
14 combination with X to facilitate some things. The window manager's job is to
15 take care of the placement of windows, to provide the user with some mechanisms
16 to change the position/size of windows and to communicate with clients to a
17 certain extent (for example handle fullscreen requests of clients such as
20 There are no different contexts in which X11 clients run, so a window manager
21 is just another client, like all other X11 applications. However, it handles
22 some events which normal clients usually don’t handle.
24 In the case of i3, the tasks (and order of them) are the following:
26 . Grab the key bindings (events will be sent upon keypress/keyrelease)
27 . Iterate through all existing windows (if the window manager is not started as
28 the first client of X) and manage them (reparent them, create window
30 . When new windows are created, manage them
31 . Handle the client’s `_WM_STATE` property, but only `_WM_STATE_FULLSCREEN` and
32 `_NET_WM_STATE_DEMANDS_ATTENTION`
33 . Handle the client’s `WM_NAME` property
34 . Handle the client’s size hints to display them proportionally
35 . Handle the client’s urgency hint
36 . Handle enter notifications (focus follows mouse)
37 . Handle button (as in mouse buttons) presses for focus/raise on click
38 . Handle expose events to re-draw own windows such as decorations
39 . React to the user’s commands: Change focus, Move windows, Switch workspaces,
40 Change the layout mode of a container (default/stacking/tabbed), start a new
41 application, restart the window manager
43 In the following chapters, each of these tasks and their implementation details
46 === Tiling window managers
48 Traditionally, there are two approaches to managing windows: The most common
49 one nowadays is floating, which means the user can freely move/resize the
50 windows. The other approach is called tiling, which means that your window
51 manager distributes windows to use as much space as possible while not
52 overlapping each other.
54 The idea behind tiling is that you should not need to waste your time
55 moving/resizing windows while you usually want to get some work done. After
56 all, most users sooner or later tend to lay out their windows in a way which
57 corresponds to tiling or stacking mode in i3. Therefore, why not let i3 do this
58 for you? Certainly, it’s faster than you could ever do it.
60 The problem with most tiling window managers is that they are too inflexible.
61 In my opinion, a window manager is just another tool, and similar to vim which
62 can edit all kinds of text files (like source code, HTML, …) and is not limited
63 to a specific file type, a window manager should not limit itself to a certain
64 layout (like dwm, awesome, …) but provide mechanisms for you to easily create
65 the layout you need at the moment.
69 The data structure which i3 uses to keep track of your windows is a tree. Every
70 node in the tree is a container (type +Con+). Some containers represent actual
71 windows (every container with a +window != NULL+), some represent split
72 containers and a few have special purposes: they represent workspaces, outputs
73 (like VGA1, LVDS1, …) or the X11 root window.
75 So, when you open a terminal and immediately open another one, they reside in
76 the same split container, which uses the default layout. In case of an empty
77 workspace, the split container we are talking about is the workspace.
79 To get an impression of how different layouts are represented, just play around
80 and look at the data structures -- they are exposed as a JSON hash. See
81 http://i3wm.org/docs/ipc.html#_tree_reply for documentation on that and an
86 include/atoms.xmacro::
87 A file containing all X11 atoms which i3 uses. This file will be included
88 various times (for defining, requesting and receiving the atoms), each time
89 with a different definition of xmacro().
92 Contains data definitions used by nearly all files. You really need to read
96 Contains forward definitions for all public functions, as well as
97 doxygen-compatible comments (so if you want to get a bit more of the big
98 picture, either browse all header files or use doxygen if you prefer that).
100 src/config_parser.c::
101 Contains a custom configuration parser. See src/command_parser.c for rationale
102 on why we use a custom parser.
105 Contains all functions which handle mouse button clicks (right mouse button
106 clicks initiate resizing and thus are relatively complex).
108 src/command_parser.c::
109 Contains a hand-written parser to parse commands (commands are what
110 you bind on keys and what you can send to i3 using the IPC interface, like
111 'move left' or 'workspace 4').
114 Contains all functions which deal with containers directly (creating
115 containers, searching containers, getting specific properties from containers,
119 Contains all functions handling the configuration file (calling the parser
120 (src/cfgparse.y) with the correct path, switching key bindings mode).
123 Contains debugging functions to print unhandled X events.
126 Functions to get/set certain EWMH properties easily.
129 Contains functions for floating mode (mostly resizing/dragging).
132 Contains all handlers for all kinds of X events (new window title, new hints,
133 unmapping, key presses, button presses, …).
136 Contains code for the IPC interface.
139 Contains code for loading layouts from JSON files.
142 Contains the logging functions.
145 Initializes the window manager.
148 Looks at existing or new windows and decides whether to manage them. If so, it
149 reparents the window and inserts it into our data structures.
152 A "match" is a data structure which acts like a mask or expression to match
153 certain windows or not. For example, when using commands, you can specify a
154 command like this: [title="*Firefox*"] kill. The title member of the match
155 data structure will then be filled and i3 will check each window using
156 match_matches_window() to find the windows affected by this command.
159 Contains code to move a container in a specific direction.
162 Functions to handle CT_OUTPUT cons.
165 The RandR API is used to get (and re-query) the configured outputs (monitors,
169 Renders the tree data structure by assigning coordinates to every node. These
170 values will later be pushed to X11 in +src/x.c+.
173 Contains the functions to resize containers.
176 Handles +SIGSEGV+, +SIGABRT+ and +SIGFPE+ by showing a dialog that i3 crashed.
177 You can chose to let it dump core, to restart it in-place or to restart it
178 in-place but forget about the layout.
181 Contains functions which open or close containers in the tree, change focus or
182 cleanup ("flatten") the tree. See also +src/move.c+ for another similar
183 function, which was moved into its own file because it is so long.
186 Contains useful functions which are not really dependant on anything.
189 Handlers to update X11 window properties like +WM_CLASS+, +_NET_WM_NAME+,
190 +CLIENT_LEADER+, etc.
193 Contains all functions related to workspaces (displaying, hiding, renaming…)
196 Transfers our in-memory tree (see +src/render.c+) to X11.
199 Contains wrappers to use xcb more easily.
202 XCursor functions (for cursor themes).
205 Legacy support for Xinerama. See +src/randr.c+ for the preferred API.
210 See include/data.h for documented data structures. The most important ones are
211 explained right here.
213 /////////////////////////////////////////////////////////////////////////////////
214 // TODO: update image
216 image:bigpicture.png[The Big Picture]
218 /////////////////////////////////////////////////////////////////////////////////
220 So, the hierarchy is:
222 . *X11 root window*, the root container
223 . *Output container* (LVDS1 in this example)
224 . *Content container* (there are also containers for dock windows)
225 . *Workspaces* (Workspace 1 in this example, with horizontal orientation)
226 . *Split container* (vertically split)
227 . *X11 window containers*
229 The data type is +Con+, in all cases.
233 The X11 root window is a single window per X11 display (a display is identified
234 by +:0+ or +:1+ etc.). The root window is what you draw your background image
235 on. It spans all the available outputs, e.g. +VGA1+ is a specific part of the
236 root window and +LVDS1+ is a specific part of the root window.
240 Every active output obtained through RandR is represented by one output
241 container. Outputs are considered active when a mode is configured (meaning
242 something is actually displayed on the output) and the output is not a clone.
244 For example, if your notebook has a screen resolution of 1280x800 px and you
245 connect a video projector with a resolution of 1024x768 px, set it up in clone
246 mode (+xrandr \--output VGA1 \--mode 1024x768 \--same-as LVDS1+), i3 will
247 reduce the resolution to the lowest common resolution and disable one of the
248 cloned outputs afterwards.
250 However, if you configure it using +xrandr \--output VGA1 \--mode 1024x768
251 \--right-of LVDS1+, i3 will set both outputs active. For each output, a new
252 workspace will be assigned. New workspaces are created on the output you are
255 === Content container
257 Each output has multiple children. Two of them are dock containers which hold
258 dock clients. The other one is the content container, which holds the actual
259 content (workspaces) of this output.
263 A workspace is identified by its name. Basically, you could think of
264 workspaces as different desks in your office, if you like the desktop
265 metaphor. They just contain different sets of windows and are completely
266 separate of each other. Other window managers also call this ``Virtual
271 A split container is a container which holds an arbitrary amount of split
272 containers or X11 window containers. It has an orientation (horizontal or
273 vertical) and a layout.
275 Split containers (and X11 window containers, which are a subtype of split
276 containers) can have different border styles.
278 === X11 window container
280 An X11 window container holds exactly one X11 window. These are the leaf nodes
281 of the layout tree, they cannot have any children.
285 i3 makes heavy use of the list macros defined in BSD operating systems. To
286 ensure that the operating system on which i3 is compiled has all the expected
287 features, i3 comes with `include/queue.h`. On BSD systems, you can use man
288 `queue(3)`. On Linux, you have to use google (or read the source).
290 The lists used are +SLIST+ (single linked lists), +CIRCLEQ+ (circular
291 queues) and +TAILQ+ (tail queues). Usually, only forward traversal is necessary,
292 so an `SLIST` works fine. If inserting elements at arbitrary positions or at
293 the end of a list is necessary, a +TAILQ+ is used instead. However, for the
294 windows inside a container, a +CIRCLEQ+ is necessary to go from the currently
295 selected window to the window above/below.
297 == Naming conventions
299 There is a row of standard variables used in many events. The following names
300 should be chosen for those:
302 * ``conn'' is the xcb_connection_t
303 * ``event'' is the event of the particular type
304 * ``con'' names a container
305 * ``current'' is a loop variable when using +TAILQ_FOREACH+ etc.
307 == Startup (src/mainx.c, main())
309 * Establish the xcb connection
310 * Check for XKB extension on the separate X connection, load Xcursor
311 * Check for RandR screens (with a fall-back to Xinerama)
312 * Grab the keycodes for which bindings exist
313 * Manage all existing windows
314 * Enter the event loop
318 === Grabbing the bindings
320 Grabbing the bindings is quite straight-forward. You pass X your combination of
321 modifiers and the keycode you want to grab and whether you want to grab them
322 actively or passively. Most bindings (everything except for bindings using
323 Mode_switch) are grabbed passively, that is, just the window manager gets the
324 event and cannot replay it.
326 We need to grab bindings that use Mode_switch actively because of a bug in X.
327 When the window manager receives the keypress/keyrelease event for an actively
328 grabbed keycode, it has to decide what to do with this event: It can either
329 replay it so that other applications get it or it can prevent other
330 applications from receiving it.
332 So, why do we need to grab keycodes actively? Because X does not set the
333 state-property of keypress/keyrelease events properly. The Mode_switch bit is
334 not set and we need to get it using XkbGetState. This means we cannot pass X
335 our combination of modifiers containing Mode_switch when grabbing the key and
336 therefore need to grab the keycode itself without any modifiers. This means,
337 if you bind Mode_switch + keycode 38 ("a"), i3 will grab keycode 38 ("a") and
338 check on each press of "a" if the Mode_switch bit is set using XKB. If yes, it
339 will handle the event, if not, it will replay the event.
341 === Handling a keypress
343 As mentioned in "Grabbing the bindings", upon a keypress event, i3 first gets
346 Then, it looks through all bindings and gets the one which matches the received
349 The bound command is parsed by the cmdparse lexer/parser, see +parse_cmd+ in
352 == Manage windows (src/main.c, manage_window() and reparent_window())
354 `manage_window()` does some checks to decide whether the window should be
357 * Windows have to be mapped, that is, visible on screen
358 * The override_redirect must not be set. Windows with override_redirect shall
359 not be managed by a window manager
361 Afterwards, i3 gets the initial geometry and reparents the window (see
362 `reparent_window()`) if it wasn’t already managed.
364 Reparenting means that for each window which is reparented, a new window,
365 slightly larger than the original one, is created. The original window is then
366 reparented to the bigger one (called "frame").
368 After reparenting, the window type (`_NET_WM_WINDOW_TYPE`) is checked to see
369 whether this window is a dock (`_NET_WM_WINDOW_TYPE_DOCK`), like dzen2 for
370 example. Docks are handled differently, they don’t have decorations and are not
371 assigned to a specific container. Instead, they are positioned at the bottom
372 or top of the screen (in the appropriate dock area containers). To get the
373 height which needs to be reserved for the window, the `_NET_WM_STRUT_PARTIAL`
376 Furthermore, the list of assignments (to other workspaces, which may be on
377 other screens) is checked. If the window matches one of the user’s criteria,
378 it may either be put in floating mode or moved to a different workspace. If the
379 target workspace is not visible, the window will not be mapped.
381 == What happens when an application is started?
383 i3 does not care about applications. All it notices is when new windows are
384 mapped (see `src/handlers.c`, `handle_map_request()`). The window is then
385 reparented (see section "Manage windows").
387 After reparenting the window, `render_tree()` is called which renders the
388 internal layout table. The new window has been placed in the currently focused
389 container and therefore the new window and the old windows (if any) need to be
390 moved/resized so that the currently active layout (default/stacking/tabbed mode)
391 is rendered correctly. To move/resize windows, a window is ``configured'' in
394 Some applications, such as MPlayer obviously assume the window manager is
395 stupid and try to configure their windows by themselves. This generates an
396 event called configurerequest. i3 handles these events and tells the window the
397 size it had before the configurerequest (with the exception of not yet mapped
398 windows, which get configured like they want to, and floating windows, which
399 can reconfigure themselves).
403 Only the _NET_WM_STATE_FULLSCREEN atom is handled. It calls
404 ``toggle_fullscreen()'' for the specific client which just configures the
405 client to use the whole screen on which it currently is. Also, it is set as
406 fullscreen_client for the i3Screen.
410 When the WM_NAME property of a window changes, its decoration (containing the
411 title) is re-rendered. Note that WM_NAME is in COMPOUND_TEXT encoding which is
412 totally uncommon and cumbersome. Therefore, the _NET_WM_NAME atom will be used
417 Like WM_NAME, this atom contains the title of a window. However, _NET_WM_NAME
418 is encoded in UTF-8. i3 will recode it to UCS-2 in order to be able to pass it
419 to X. Using an appropriate font (ISO-10646), you can see most special
420 characters (every special character contained in your font).
424 Size hints specify the minimum/maximum size for a given window as well as its
425 aspect ratio. This is important for clients like mplayer, who only set the
426 aspect ratio and resize their window to be as small as possible (but only with
427 some video outputs, for example in Xv, while when using x11, mplayer does the
428 necessary centering for itself).
430 So, when an aspect ratio was specified, i3 adjusts the height of the window
431 until the size maintains the correct aspect ratio. For the code to do this, see
432 src/layout.c, function resize_client().
434 == Rendering (src/layout.c, render_layout() and render_container())
436 Rendering in i3 version 4 is the step which assigns the correct sizes for
437 borders, decoration windows, child windows and the stacking order of all
438 windows. In a separate step (+x_push_changes()+), these changes are pushed to
441 Keep in mind that all these properties (+rect+, +window_rect+ and +deco_rect+)
442 are temporary, meaning they will be overwritten by calling +render_con+.
443 Persistent position/size information is kept in +geometry+.
445 The entry point for every rendering operation (except for the case of moving
446 floating windows around) currently is +tree_render()+ which will re-render
447 everything that’s necessary (for every output, only the currently displayed
448 workspace is rendered). This behavior is expected to change in the future,
449 since for a lot of updates, re-rendering everything is not actually necessary.
450 Focus was on getting it working correct, not getting it work very fast.
452 What +tree_render()+ actually does is calling +render_con()+ on the root
453 container and then pushing the changes to X11. The following sections talk
454 about the different rendering steps, in the order of "top of the tree" (root
455 container) to the bottom.
457 === Rendering the root container
459 The i3 root container (`con->type == CT_ROOT`) represents the X11 root window.
460 It contains one child container for every output (like LVDS1, VGA1, …), which
461 is available on your computer.
463 Rendering the root will first render all tiling windows and then all floating
464 windows. This is necessary because a floating window can be positioned in such
465 a way that it is visible on two different outputs. Therefore, by first
466 rendering all the tiling windows (of all outputs), we make sure that floating
467 windows can never be obscured by tiling windows.
469 Essentially, though, this code path will just call +render_con()+ for every
470 output and +x_raise_con(); render_con()+ for every floating window.
472 In the special case of having a "global fullscreen" window (fullscreen mode
473 spanning all outputs), a shortcut is taken and +x_raise_con(); render_con()+ is
474 only called for the global fullscreen window.
476 === Rendering an output
478 Output containers (`con->layout == L_OUTPUT`) represent a hardware output like
479 LVDS1, VGA1, etc. An output container has three children (at the moment): One
480 content container (having workspaces as children) and the top/bottom dock area
483 The rendering happens in the function +render_l_output()+ in the following
486 1. Find the content container (`con->type == CT_CON`)
487 2. Get the currently visible workspace (+con_get_fullscreen_con(content,
489 3. If there is a fullscreened window on that workspace, directly render it and
490 return, thus ignoring the dock areas.
491 4. Sum up the space used by all the dock windows (they have a variable height
493 5. Set the workspace rects (x/y/width/height) based on the position of the
494 output (stored in `con->rect`) and the usable space
495 (`con->rect.{width,height}` without the space used for dock windows).
496 6. Recursively raise and render the output’s child containers (meaning dock
497 area containers and the content container).
499 === Rendering a workspace or split container
501 From here on, there really is no difference anymore. All containers are of
502 `con->type == CT_CON` (whether workspace or split container) and some of them
503 have a `con->window`, meaning they represent an actual window instead of a
508 In default layout, containers are placed horizontally or vertically next to
509 each other (depending on the `con->orientation`). If a child is a leaf node (as
510 opposed to a split container) and has border style "normal", appropriate space
511 will be reserved for its window decoration.
515 In stacked layout, only the focused window is actually shown (this is achieved
516 by calling +x_raise_con()+ in reverse focus order at the end of +render_con()+).
518 The available space for the focused window is the size of the container minus
519 the height of the window decoration for all windows inside this stacked
522 If border style is "1pixel" or "none", no window decoration height will be
523 reserved (or displayed later on), unless there is more than one window inside
524 the stacked container.
528 Tabbed layout works precisely like stacked layout, but the window decoration
529 position/size is different: They are placed next to each other on a single line
532 ==== Dock area layout
534 This is a special case. Users cannot choose the dock area layout, but it will be
535 set for the dock area containers. In the dockarea layout (at the moment!),
536 windows will be placed above each other.
538 === Rendering a window
540 A window’s size and position will be determined in the following way:
542 1. Subtract the border if border style is not "none" (but "normal" or "1pixel").
543 2. Subtract the X11 border, if the window has an X11 border > 0.
544 3. Obey the aspect ratio of the window (think MPlayer).
545 4. Obey the height- and width-increments of the window (think terminal emulator
546 which can only be resized in one-line or one-character steps).
548 == Pushing updates to X11 / Drawing
550 A big problem with i3 before version 4 was that we just sent requests to X11
551 anywhere in the source code. This was bad because nobody could understand the
552 entirety of our interaction with X11, it lead to subtle bugs and a lot of edge
553 cases which we had to consider all over again.
555 Therefore, since version 4, we have a single file, +src/x.c+, which is
556 responsible for repeatedly transferring parts of our tree datastructure to X11.
558 +src/x.c+ consists of multiple parts:
560 1. The state pushing: +x_push_changes()+, which calls +x_push_node()+.
561 2. State modification functions: +x_con_init+, +x_reinit+,
562 +x_reparent_child+, +x_move_win+, +x_con_kill+, +x_raise_con+, +x_set_name+
564 3. Expose event handling (drawing decorations): +x_deco_recurse()+ and
565 +x_draw_decoration()+.
567 === Pushing state to X11
569 In general, the function +x_push_changes+ should be called to push state
570 changes. Only when the scope of the state change is clearly defined (for
571 example only the title of a window) and its impact is known beforehand, one can
572 optimize this and call +x_push_node+ on the appropriate con directly.
574 +x_push_changes+ works in the following steps:
576 1. Clear the eventmask for all mapped windows. This leads to not getting
577 useless ConfigureNotify or EnterNotify events which are caused by our
578 requests. In general, we only want to handle user input.
579 2. Stack windows above each other, in reverse stack order (starting with the
580 most obscured/bottom window). This is relevant for floating windows which
581 can overlap each other, but also for tiling windows in stacked or tabbed
582 containers. We also update the +_NET_CLIENT_LIST_STACKING+ hint which is
583 necessary for tab drag and drop in Chromium.
584 3. +x_push_node+ will be called for the root container, recursively calling
585 itself for the container’s children. This function actually pushes the
586 state, see the next paragraph.
587 4. If the pointer needs to be warped to a different position (for example when
588 changing focus to a differnt output), it will be warped now.
589 5. The eventmask is restored for all mapped windows.
590 6. Window decorations will be rendered by calling +x_deco_recurse+ on the root
591 container, which then recursively calls itself for the children.
592 7. If the input focus needs to be changed (because the user focused a different
593 window), it will be updated now.
594 8. +x_push_node_unmaps+ will be called for the root container. This function
595 only pushes UnmapWindow requests. Separating the state pushing is necessary
596 to handle fullscreen windows (and workspace switches) in a smooth fashion:
597 The newly visible windows should be visible before the old windows are
600 +x_push_node+ works in the following steps:
602 1. Update the window’s +WM_NAME+, if changed (the +WM_NAME+ is set on i3
603 containers mainly for debugging purposes).
604 2. Reparents a child window into the i3 container if the container was created
605 for a specific managed window.
606 3. If the size/position of the i3 container changed (due to opening a new
607 window or switching layouts for example), the window will be reconfigured.
608 Also, the pixmap which is used to draw the window decoration/border on is
609 reconfigured (pixmaps are size-dependent).
610 4. Size/position for the child window is adjusted.
611 5. The i3 container is mapped if it should be visible and was not yet mapped.
612 When mapping, +WM_STATE+ is set to +WM_STATE_NORMAL+. Also, the eventmask of
613 the child window is updated and the i3 container’s contents are copied from
615 6. +x_push_node+ is called recursively for all children of the current
618 +x_push_node_unmaps+ handles the remaining case of an i3 container being
619 unmapped if it should not be visible anymore. +WM_STATE+ will be set to
620 +WM_STATE_WITHDRAWN+.
623 === Drawing window decorations/borders/backgrounds
625 +x_draw_decoration+ draws window decorations. It is run for every leaf
626 container (representing an actual X11 window) and for every non-leaf container
627 which is in a stacked/tabbed container (because stacked/tabbed containers
628 display a window decoration for split containers, which at the moment just says
629 "another container").
631 Then, parameters are collected to be able to determine whether this decoration
632 drawing is actually necessary or was already done. This saves a substantial
633 number of redraws (depending on your workload, but far over 50%).
635 Assuming that we need to draw this decoration, we start by filling the empty
636 space around the child window (think of MPlayer with a specific aspect ratio)
637 in the user-configured client background color.
639 Afterwards, we draw the appropriate border (in case of border styles "normal"
640 and "1pixel") and the top bar (in case of border style "normal").
642 The last step is drawing the window title on the top bar.
645 /////////////////////////////////////////////////////////////////////////////////
647 == Resizing containers
649 By clicking and dragging the border of a container, you can resize the whole
650 column (respectively row) which this container is in. This is necessary to keep
651 the table layout working and consistent.
653 The resizing works similarly to the resizing of floating windows or movement of
656 * A new, invisible window with the size of the root window is created
658 * Another window, 2px width and as high as your screen (or vice versa for
659 horizontal resizing) is created. Its background color is the border color and
660 it is only there to inform the user how big the container will be (it
661 creates the impression of dragging the border out of the container).
662 * The +drag_pointer+ function of +src/floating.c+ is called to grab the pointer
663 and enter its own event loop which will pass all events (expose events) but
664 motion notify events. This function then calls the specified callback
665 (+resize_callback+) which does some boundary checking and moves the helper
666 window. As soon as the mouse button is released, this loop will be
668 * The new width_factor for each involved column (respectively row) will be
671 /////////////////////////////////////////////////////////////////////////////////
673 == User commands (parser-specs/commands.spec)
675 In the configuration file and when using i3 interactively (with +i3-msg+, for
676 example), you use commands to make i3 do things, like focus a different window,
677 set a window to fullscreen, and so on. An example command is +floating enable+,
678 which enables floating mode for the currently focused window. See the
679 appropriate section in the link:userguide.html[User’s Guide] for a reference of
682 In earlier versions of i3, interpreting these commands was done using lex and
683 yacc, but experience has shown that lex and yacc are not well suited for our
684 command language. Therefore, starting from version 4.2, we use a custom parser
685 for user commands (not yet for the configuration file).
686 The input specification for this parser can be found in the file
687 +parser-specs/commands.spec+. Should you happen to use Vim as an editor, use
688 :source parser-specs/highlighting.vim to get syntax highlighting for this file
689 (highlighting files for other editors are welcome).
691 .Excerpt from commands.spec
692 -----------------------------------------------------------------------
694 '[' -> call cmd_criteria_init(); CRITERIA
697 'workspace' -> WORKSPACE
698 'exit' -> call cmd_exit()
699 'restart' -> call cmd_restart()
700 'reload' -> call cmd_reload()
701 -----------------------------------------------------------------------
703 The input specification is written in an extremely simple format. The
704 specification is then converted into C code by the Perl script
705 generate-commands-parser.pl (the output file names begin with GENERATED and the
706 files are stored in the +include+ directory). The parser implementation
707 +src/commands_parser.c+ includes the generated C code at compile-time.
709 The above excerpt from commands.spec illustrates nearly all features of our
710 specification format: You describe different states and what can happen within
711 each state. State names are all-caps; the state in the above excerpt is called
712 INITIAL. A list of tokens and their actions (separated by an ASCII arrow)
713 follows. In the excerpt, all tokens are literals, that is, simple text strings
714 which will be compared with the input. An action is either the name of a state
715 in which the parser will transition into, or the keyword 'call', followed by
716 the name of a function (and optionally a state).
718 === Example: The WORKSPACE state
720 Let’s have a look at the WORKSPACE state, which is a good example of all
721 features. This is its definition:
723 .WORKSPACE state (commands.spec)
724 ----------------------------------------------------------------
725 # workspace next|prev|next_on_output|prev_on_output
726 # workspace back_and_forth
729 direction = 'next_on_output', 'prev_on_output', 'next', 'prev'
730 -> call cmd_workspace($direction)
732 -> call cmd_workspace_back_and_forth()
734 -> call cmd_workspace_name($workspace)
735 ----------------------------------------------------------------
737 As you can see from the commands, there are multiple different valid variants
738 of the workspace command:
740 workspace <direction>::
741 The word 'workspace' can be followed by any of the tokens 'next',
742 'prev', 'next_on_output' or 'prev_on_output'. This command will
743 switch to the next or previous workspace (optionally on the same
745 There is one function called +cmd_workspace+, which is defined
746 in +src/commands.c+. It will handle this kind of command. To know which
747 direction was specified, the direction token is stored on the stack
748 with the name "direction", which is what the "direction = " means in
751 NOTE: Note that you can specify multiple literals in the same line. This has
752 exactly the same effect as if you specified `direction =
753 'next_on_output' -> call cmd_workspace($direction)` and so forth. +
755 NOTE: Also note that the order of literals is important here: If 'next' were
756 ordered before 'next_on_output', then 'next_on_output' would never
759 workspace back_and_forth::
760 This is a very simple case: When the literal 'back_and_forth' is found
761 in the input, the function +cmd_workspace_back_and_forth+ will be
762 called without parameters and the parser will return to the INITIAL
763 state (since no other state was specified).
765 In this case, the workspace command is followed by an arbitrary string,
766 possibly in quotes, for example "workspace 3" or "workspace bleh". +
767 This is the first time that the token is actually not a literal (not in
768 single quotes), but just called string. Other possible tokens are word
769 (the same as string, but stops matching at a whitespace) and end
770 (matches the end of the input).
772 === Introducing a new command
774 The following steps have to be taken in order to properly introduce a new
775 command (or possibly extend an existing command):
777 1. Define a function beginning with +cmd_+ in the file +src/commands.c+. Copy
778 the prototype of an existing function.
779 2. After adding a comment on what the function does, copy the comment and
780 function definition to +include/commands.h+. Make the comment in the header
781 file use double asterisks to make doxygen pick it up.
782 3. Write a test case (or extend an existing test case) for your feature, see
783 link:testsuite.html[i3 testsuite]. For now, it is sufficient to simply call
784 your command in all the various possible ways.
785 4. Extend the parser specification in +parser-specs/commands.spec+. Run the
786 testsuite and see if your new function gets called with the appropriate
787 arguments for the appropriate input.
788 5. Actually implement the feature.
789 6. Document the feature in the link:userguide.html[User’s Guide].
793 The movement code is pretty delicate. You need to consider all cases before
794 making any changes or before being able to fully understand how it works.
796 === Case 1: Moving inside the same container
798 The reference layout for this case is a single workspace in horizontal
799 orientation with two containers on it. Focus is on the left container (1).
802 [width="15%",cols="^,^"]
807 When moving the left window to the right (command +move right+), tree_move will
808 look for a container with horizontal orientation and finds the parent of the
809 left container, that is, the workspace. Afterwards, it runs the code branch
810 commented with "the easy case": it calls TAILQ_NEXT to get the container right
811 of the current one and swaps both containers.
813 === Case 2: Move a container into a split container
815 The reference layout for this case is a horizontal workspace with two
816 containers. The right container is a v-split with two containers. Focus is on
817 the left container (1).
819 [width="15%",cols="^,^"]
825 When moving to the right (command +move right+), i3 will work like in case 1
826 ("the easy case"). However, as the right container is not a leaf container, but
827 a v-split, the left container (1) will be inserted at the right position (below
828 2, assuming that 2 is focused inside the v-split) by calling +insert_con_into+.
830 +insert_con_into+ detaches the container from its parent and inserts it
831 before/after the given target container. Afterwards, the on_remove_child
832 callback is called on the old parent container which will then be closed, if
835 Afterwards, +con_focus+ will be called to fix the focus stack and the tree will
838 === Case 3: Moving to non-existant top/bottom
840 Like in case 1, the reference layout for this case is a single workspace in
841 horizontal orientation with two containers on it. Focus is on the left
844 [width="15%",cols="^,^"]
849 This time however, the command is +move up+ or +move down+. tree_move will look
850 for a container with vertical orientation. As it will not find any,
851 +same_orientation+ is NULL and therefore i3 will perform a forced orientation
852 change on the workspace by creating a new h-split container, moving the
853 workspace contents into it and then changing the workspace orientation to
854 vertical. Now it will again search for parent containers with vertical
855 orientation and it will find the workspace.
857 This time, the easy case code path will not be run as we are not moving inside
858 the same container. Instead, +insert_con_into+ will be called with the focused
859 container and the container above/below the current one (on the level of
862 Now, +con_focus+ will be called to fix the focus stack and the tree will be
865 === Case 4: Moving to existant top/bottom
867 The reference layout for this case is a vertical workspace with two containers.
868 The bottom one is a h-split containing two containers (1 and 2). Focus is on
869 the bottom left container (1).
871 [width="15%",cols="^,^"]
877 This case is very much like case 3, only this time the forced workspace
878 orientation change does not need to be performed because the workspace already
879 is in vertical orientation.
881 === Case 5: Moving in one-child h-split
883 The reference layout for this case is a horizontal workspace with two
884 containers having a v-split on the left side with a one-child h-split on the
885 bottom. Focus is on the bottom left container (2(h)):
887 [width="15%",cols="^,^"]
893 In this case, +same_orientation+ will be set to the h-split container around
894 the focused container. However, when trying the easy case, the next/previous
895 container +swap+ will be NULL. Therefore, i3 will search again for a
896 +same_orientation+ container, this time starting from the parent of the h-split
899 After determining a new +same_orientation+ container (if it is NULL, the
900 orientation will be force-changed), this case is equivalent to case 2 or case
904 === Case 6: Floating containers
906 The reference layout for this case is a horizontal workspace with two
907 containers plus one floating h-split container. Focus is on the floating
910 TODO: nice illustration. table not possible?
912 When moving up/down, the container needs to leave the floating container and it
913 needs to be placed on the workspace (at workspace level). This is accomplished
914 by calling the function +attach_to_workspace+.
918 Without much ado, here is the list of cases which need to be considered:
920 * click to focus (tiling + floating) and raise (floating)
921 * click to focus/raise when in stacked/tabbed mode
922 * floating_modifier + left mouse button to drag a floating con
923 * floating_modifier + right mouse button to resize a floating con
924 * click on decoration in a floating con to either initiate a resize (if there
925 is more than one child in the floating con) or to drag the
926 floating con (if it’s the one at the top).
927 * click on border in a floating con to resize the floating con
928 * floating_modifier + right mouse button to resize a tiling con
929 * click on border/decoration to resize a tiling con
933 * Forgetting to call `xcb_flush(conn);` after sending a request. This usually
934 leads to code which looks like it works fine but which does not work under
937 * Forgetting to call `floating_fix_coordinates(con, old_rect, new_rect)` after
938 moving workspaces across outputs. Coordinates for floating containers are
939 not relative to workspace boundaries, so you must correct their coordinates
940 or those containers will show up in the wrong workspace or not at all.
942 == Using git / sending patches
946 For a short introduction into using git, see
947 http://web.archive.org/web/20121024222556/http://www.spheredev.org/wiki/Git_for_the_lazy
948 or, for more documentation, see http://git-scm.com/documentation
950 Please talk to us before working on new features to see whether they will be
951 accepted. There are a few things which we don’t want to see in i3, e.g. a
952 command which will focus windows in an alt+tab like way.
954 When working on bugfixes, please make sure you mention that you are working on
955 it in the corresponding bugreport at http://bugs.i3wm.org/. In case there is no
956 bugreport yet, please create one.
958 After you are done, please submit your work for review at http://cr.i3wm.org/
960 Do not send emails to the mailing list or any author directly, and don’t submit
961 them in the bugtracker, since all reviews should be done in public at
962 http://cr.i3wm.org/. In order to make your review go as fast as possible, you
963 could have a look at previous reviews and see what the common mistakes are.
965 === Which branch to use?
967 Work on i3 generally happens in two branches: “master” and “next”. Since
968 “master” is what people get when they check out the git repository, its
969 contents are always stable. That is, it contains the source code of the latest
970 release, plus any bugfixes that were applied since that release.
972 New features are only found in the “next” branch. Therefore, if you are working
973 on a new feature, use the “next” branch. If you are working on a bugfix, use
974 the “next” branch, too, but make sure your code also works on “master”.
976 == Thought experiments
978 In this section, we collect thought experiments, so that we don’t forget our
979 thoughts about specific topics. They are not necessary to get into hacking i3,
980 but if you are interested in one of the topics they cover, you should read them
981 before asking us why things are the way they are or why we don’t implement
984 === Using cgroups per workspace
986 cgroups (control groups) are a linux-only feature which provides the ability to
987 group multiple processes. For each group, you can individually set resource
988 limits, like allowed memory usage. Furthermore, and more importantly for our
989 purposes, they serve as a namespace, a label which you can attach to processes
992 One interesting use for cgroups is having one cgroup per workspace (or
993 container, doesn’t really matter). That way, you could set different priorities
994 and have a workspace for important stuff (say, writing a LaTeX document or
995 programming) and a workspace for unimportant background stuff (say,
996 JDownloader). Both tasks can obviously consume a lot of I/O resources, but in
997 this example it doesn’t really matter if JDownloader unpacks the download a
998 minute earlier or not. However, your compiler should work as fast as possible.
999 Having one cgroup per workspace, you would assign more resources to the
1000 programming workspace.
1002 Another interesting feature is that an inherent problem of the workspace
1003 concept could be solved by using cgroups: When starting an application on
1004 workspace 1, then switching to workspace 2, you will get the application’s
1005 window(s) on workspace 2 instead of the one you started it on. This is because
1006 the window manager does not have any mapping between the process it starts (or
1007 gets started in any way) and the window(s) which appear.
1009 Imagine for example using dmenu: The user starts dmenu by pressing Mod+d, dmenu
1010 gets started with PID 3390. The user then decides to launch Firefox, which
1011 takes a long time. So he enters firefox into dmenu and presses enter. Firefox
1012 gets started with PID 4001. When it finally finishes loading, it creates an X11
1013 window and uses MapWindow to make it visible. This is the first time i3
1014 actually gets in touch with Firefox. It decides to map the window, but it has
1015 no way of knowing that this window (even though it has the _NET_WM_PID property
1016 set to 4001) belongs to the dmenu the user started before.
1018 How do cgroups help with this? Well, when pressing Mod+d to launch dmenu, i3
1019 would create a new cgroup, let’s call it i3-3390-1. It launches dmenu in that
1020 cgroup, which gets PID 3390. As before, the user enters firefox and Firefox
1021 gets launched with PID 4001. This time, though, the Firefox process with PID
1022 4001 is *also* member of the cgroup i3-3390-1 (because fork()ing in a cgroup
1023 retains the cgroup property). Therefore, when mapping the window, i3 can look
1024 up in which cgroup the process is and can establish a mapping between the
1025 workspace and the window.
1027 There are multiple problems with this approach:
1029 . Every application has to properly set +_NET_WM_PID+. This is acceptable and
1030 patches can be written for the few applications which don’t set the hint yet.
1031 . It does only work on Linux, since cgroups are a Linux-only feature. Again,
1033 . The main problem is that some applications create X11 windows completely
1034 independent of UNIX processes. An example for this is Chromium (or
1035 gnome-terminal), which, when being started a second time, communicates with
1036 the first process and lets the first process open a new window. Therefore, if
1037 you have a Chromium window on workspace 2 and you are currently working on
1038 workspace 3, starting +chromium+ does not lead to the desired result (the
1039 window will open on workspace 2).
1041 Therefore, my conclusion is that the only proper way of fixing the "window gets
1042 opened on the wrong workspace" problem is in the application itself. Most
1043 modern applications support freedesktop startup-notifications which can be