3 Michael Stapelberg <michael+i3@stapelberg.de>
6 This document is intended to be the first thing you read before looking and/or touching
7 i3’s source code. It should contain all important information to help you understand
8 why things are like they are. If it does not mention something you find necessary, please
9 do not hesitate to contact me.
13 A window manager is not necessarily needed to run X, but it is usually used in combination
14 to facilitate some things. The window manager's job is to take care of the placement of
15 windows, to provide the user some mechanisms to change the position/size of windows and
16 to communicate with clients to a certain extent (for example handle fullscreen requests
17 of clients such as MPlayer).
19 There are no different contexts in which X11 clients run, so a window manager is just another
20 client, like all other X11 applications. However, it handles some events which normal clients
23 In the case of i3, the tasks (and order of them) are the following:
25 . Grab the key bindings (events will be sent upon keypress/keyrelease)
26 . Iterate through all existing windows (if the window manager is not started as the first
27 client of X) and manage them (= reparent them, create window decorations)
28 . When new windows are created, manage them
29 . Handle the client’s `_WM_STATE` property, but only the `_WM_STATE_FULLSCREEN`
30 . Handle the client’s `WM_NAME` property
31 . Handle the client’s size hints to display them proportionally
32 . Handle enter notifications (focus follows mouse)
33 . Handle button (as in mouse buttons) presses for focus/raise on click
34 . Handle expose events to re-draw own windows such as decorations
35 . React to the user’s commands: Change focus, Move windows, Switch workspaces,
36 Change the layout mode of a container (default/stacking), Start a new application,
37 Restart the window manager
39 In the following chapters, each of these tasks and their implementation details will be discussed.
41 === Tiling window managers
43 Traditionally, there are two approaches to managing windows: The most common one nowadays is
44 floating, which means the user can freely move/resize the windows. The other approach is called
45 tiling, which means that your window manager distributing windows to use as much space as
46 possible while not overlapping.
48 The idea behind tiling is that you should not need to waste your time moving/resizing windows
49 while you usually want to get some work done. After all, most users sooner or later tend to
50 lay out their windows in a way which corresponds to tiling or stacking mode in i3. Therefore,
51 why not let i3 do this for you? Certainly, it’s faster than you could ever do it.
53 The problem with most tiling window managers is that they are too unflexible. In my opinion, a
54 window manager is just another tool, and similar to vim which can edit all kinds of text files
55 (like source code, HTML, …) and is not limited to a specific file type, a window manager should
56 not limit itself to a certain layout (like dwm, awesome, …) but provide mechanisms for you to
57 easily create the layout you need at the moment.
61 To accomplish flexible layouts, we decided to simply use a table. The table grows and shrinks
62 as you need it. Each cell holds a container which then holds windows (see picture below). You
63 can use different layouts for each container (default layout and stacking layout).
65 So, when you open a terminal and immediately open another one, they reside in the same container,
66 in default layout. The layout table has exactly one column, one row and therefore one cell.
67 When you move one of the terminals to the right, the table needs to grow. It will be expanded
68 to two columns and one row. This enables you to have different layouts for each container.
69 The table then looks like this:
71 [width="15%",cols="^,^"]
76 When moving terminal 2 to the bottom, the table will be expanded again.
78 [width="15%",cols="^,^"]
84 You can really think of the layout table like a traditional HTML table, if you’ve ever
85 designed one. Especially col- and rowspan work equally. Below you see an example of
86 colspan=2 for the first container (which has T1 as window).
88 [width="15%",cols="^asciidoc"]
92 [cols="^,^",frame="none"]
98 Furthermore, you can freely resize table cells.
103 Contains data definitions used by nearly all files. You really need to read this first.
106 Contains forward definitions for all public functions, aswell as doxygen-compatible
107 comments (so if you want to get a bit more of the big picture, either browse all
108 header files or use doxygen if you prefer that).
111 Contains all functions which are specific to a certain client (make it
112 fullscreen, see if its class/name matches a pattern, kill it, …).
115 Parsing commands and actually execute them (focussing, moving, …).
118 Parses the configuration file.
121 Contains debugging functions to print unhandled X events.
124 Contains functions for floating mode (mostly resizing/dragging).
127 Contains all handlers for all kind of X events (new window title, new hints,
128 unmapping, key presses, button presses, …).
131 Renders your layout (screens, workspaces, containers).
134 Initializes the window manager.
137 Looks at existing or new windows and decides whether to manage them. If so, it
138 reparents the window and inserts it into our data structures.
141 Contains the functions to resize columns/rows in the table.
144 Manages the most important internal data structure, the design table.
147 Contains useful functions which are not really dependant on anything.
150 Contains wrappers to use xcb more easily.
153 (Re-)initializes the available screens and converts them to virtual screens (see below).
157 See include/data.h for documented data structures. The most important ones are explained
160 image:bigpicture.png[The Big Picture]
162 So, the hierarchy is:
164 . *Virtual screens* (Screen 0 in this example)
165 . *Workspaces* (Workspace 1 in this example)
166 . *Table* (There can only be one table per Workspace)
167 . *Container* (left and right in this example)
168 . *Client* (The two clients in the left container)
172 A virtual screen (type `i3Screen`) is generated from the connected screens obtained
173 through Xinerama. The difference to the raw Xinerama monitors as seen when using +xrandr(1)+
174 is that it falls back to the lowest common resolution of the logical screens.
176 For example, if your notebook has 1280x800 and you connect a video projector with
177 1024x768, set up in clone mode (+xrandr \--output VGA \--mode 1024x768 \--same-as LVDS+),
178 i3 will have one virtual screen.
180 However, if you configure it using +xrandr \--output VGA \--mode 1024x768 \--right-of LVDS+,
181 i3 will generate two virtual screens. For each virtual screen, a new workspace will be
182 assigned. New workspaces are created on the screen you are currently on.
186 A workspace is identified by its number. Basically, you could think of workspaces
187 as different desks in your bureau, if you like the desktop methaphor. They just contain
188 different sets of windows and are completely separate of each other. Other window
189 managers also call this ``Virtual desktops''.
193 Each workspace has a table, which is just a two-dimensional dynamic array containing
194 Containers (see below). This table grows and shrinks as you need it (by moving windows
195 to the right you can create a new column in the table, by moving them to the bottom
196 you create a new row).
200 A container is the content of a table’s cell. It holds an arbitrary amount of windows
201 and has a specific layout (default layout or stack layout). Containers can consume
202 multiple table cells by modifying their colspan/rowspan attribute.
206 A client is x11-speak for a window.
210 i3 makes heavy use of the list macros defined in BSD operating systems. To ensure
211 that the operating system on which i3 is compiled has all the awaited features,
212 i3 comes with `include/queue.h`. On BSD systems, you can use man `queue(3)`. On Linux,
213 you have to use google.
215 The lists used are `SLIST` (single linked lists) and `CIRCLEQ` (circular queues).
216 Usually, only forward traversal is necessary, so an `SLIST` works fine. However,
217 for the windows inside a container, a `CIRCLEQ` is necessary to go from the currently
218 selected window to the window above/below.
220 == Naming conventions
222 There is a row of standard variables used in many events. The following names should be
225 * ``conn'' is the xcb_connection_t
226 * ``event'' is the event of the particular type
227 * ``container'' names a container
228 * ``client'' names a client, for example when using a `CIRCLEQ_FOREACH`
230 == Startup (src/mainx.c, main())
232 * Establish the xcb connection
233 * Check for XKB extension on the separate X connection
234 * Check for Xinerama screens
235 * Grab the keycodes for which bindings exist
236 * Manage all existing windows
237 * Enter the event loop
241 === Grabbing the bindings
243 Grabbing the bindings is quite straight-forward. You pass X your combination of modifiers and
244 the keycode you want to grab and whether you want to grab them actively or passively. Most
245 bindings (everything except for bindings using Mode_switch) are grabbed passively, that is,
246 just the window manager gets the event and cannot replay it.
248 We need to grab bindings that use Mode_switch actively because of a bug in X. When the window
249 manager receives the keypress/keyrelease event for an actively grabbed keycode, it has to decide
250 what to do with this event: It can either replay it so that other applications get it or it
251 can prevent other applications from receiving it.
253 So, why do we need to grab keycodes actively? Because X does not set the state-property of
254 keypress/keyrelease events properly. The Mode_switch bit is not set and we need to get it
255 using XkbGetState. This means we cannot pass X our combination of modifiers containing Mode_switch
256 when grabbing the key and therefore need to grab the keycode itself without any modiffiers.
257 This means, if you bind Mode_switch + keycode 38 ("a"), i3 will grab keycode 38 ("a") and
258 check on each press of "a" if the Mode_switch bit is set using XKB. If yes, it will handle
259 the event, if not, it will replay the event.
261 === Handling a keypress
263 As mentioned in "Grabbing the bindings", upon a keypress event, i3 first gets the correct state.
265 Then, it looks through all bindings and gets the one which matches the received event.
267 The bound command is parsed directly in command mode.
269 == Manage windows (src/mainx.c, manage_window() and reparent_window())
271 `manage_window()` does some checks to decide whether the window should be managed at all:
273 * Windows have to be mapped, that is, visible on screen
274 * The override_redirect must not be set. Windows with override_redirect shall not be
275 managed by a window manager
277 Afterwards, i3 gets the intial geometry and reparents the window if it wasn’t already
280 Reparenting means that for each window which is reparented, a new window, slightly larger
281 than the original one, is created. The original window is then reparented to the bigger one
284 After reparenting, the window type (`_NET_WM_WINDOW_TYPE`) is checked to see whether this
285 window is a dock (`_NET_WM_WINDOW_TYPE_DOCK`), like dzen2 for example. Docks are handled
286 differently, they don’t have decorations and are not assigned to a specific container.
287 Instead, they are positioned at the bottom of the screen. To get the height which needsd
288 to be reserved for the window, the `_NET_WM_STRUT_PARTIAL` property is used.
290 == What happens when an application is started?
292 i3 does not care for applications. All it notices is when new windows are mapped (see
293 `src/handlers.c`, `handle_map_notify_event()`). The window is then reparented (see section
296 After reparenting the window, `render_layout()` is called which renders the internal
297 layout table. The window was placed in the currently focused container and
298 therefore the new window and the old windows (if any) need te be moved/resized
299 so that the currently active layout (default mode/stacking mode) is rendered
300 correctly. To move/resize windows, a window is ``configured'' in X11-speak.
302 Some applications, such as MPlayer obivously assume the window manager is stupid
303 and therefore configure their windows by themselves. This generates an event called
304 configurenotify. i3 handles these events and pushes the window back to its position/size.
308 Only the _NET_WM_STATE_FULLSCREEN atom is handled. It calls ``toggle_fullscreen()'' for the
309 specific client which just configures the client to use the whole screen on which it
310 currently is. Also, it is set as fullscreen_client for the i3Screen.
314 When the WM_NAME property of a window changes, its decoration (containing the title)
319 Size hints specify the minimum/maximum size for a given window aswell as its aspect ratio.
320 At the moment, as i3 does not have a floating mode yet, only the aspect ratio is parsed.
321 This is important for clients like mplayer, who only set the aspect ratio and resize their
322 window to be as small as possible (but only with some video outputs, for example in Xv,
323 while when using x11, mplayer does the necessary centering for itself).
325 So, when an aspect ratio was specified, i3 adjusts the height of the window until the
326 size maintains the correct aspect ratio. For the code to do this, see src/layout.c,
327 function resize_client().
329 == Rendering (src/layout.c, render_layout() and render_container())
331 There are two entry points to rendering: render_layout() and render_container(). The
332 former one renders all virtual screens, the currently active workspace of each virtual
333 screen and all containers (inside the table cells) of these workspaces using
334 render_container(). Therefore, if you need to render only a single container, for
335 example because a window was removed, added or changed its title, you should directly
336 call render_container().
338 Rendering consists of two steps: In the first one, in render_layout(), each container
339 gets its position (screen offset + offset in the table) and size (container's width
340 times colspan/rowspan). Then, render_container() is called:
342 render_container() then takes different approaches, depending on the mode the container
347 On the frame (the window which was created around the client’s window for the decorations),
348 a black rectangle is drawn as a background for windows like MPlayer, which don’t completely
353 Each clients gets the container’s width and an equal amount of height.
357 In stack mode, a window containing the decorations of all windows inside the container
358 is placed at the top. The currently focused window is then given the whole remaining
361 === Window decorations
363 The window decorations consist of a rectangle in the appropriate color (depends on whether
364 this window is the currently focused one or the last focused one in a not focused container
365 or not focused at all) forming the background. Afterwards, two lighter lines are drawn
366 and the last step is drawing the window’s title (see WM_NAME) onto it.
368 === Fullscreen windows
370 For fullscreen windows, the `rect` (x, y, width, height) is not changed to allow the client
371 to easily go back to its previous position. Instead, fullscreen windows are skipped
374 === Resizing containers
376 By clicking and dragging the border of a container, you can resize it freely.
380 == User commands / commandmode (src/commands.c)
382 Like in vim, you can control i3 using commands. They are intended to be a powerful
383 alternative to lots of shortcuts, because they can be combined. There are a few special
384 commands, which are the following:
387 Starts the given command by passing it to `/bin/sh`.
390 Restarts i3 by executing `argv[0]` (the path with which you started i3) without forking.
393 "With". This is used to select a bunch of windows. Currently, only selecting the whole
394 container in which the window is in, is supported by specifying "w".
397 Toggle fullscreen, stacking, default mode for the current window/container.
399 The other commands are to be combined with a direction. The directions are h, j, k and l,
400 like in vim (h = left, j = down, k = up, l = right). When you just specify the direction
401 keys, i3 will move the focus in that direction. You can provide "m" or "s" before the
402 direction to move a window respectively or snap.
406 * Forgetting to call `xcb_flush(conn);` after sending a request. This usually leads to
407 code which looks like it works fine but which does not work under certain conditions.
409 == Using git / sending patches
411 For a short introduction into using git, see TODO.
413 When you want to send a patch because you fixed a bug or implemented a cool feature (please
414 talk to us before working on features to see whether they are maybe already implemented, not
415 possible because of some reason or don’t fit into the concept), please use git to create
418 First of all, update your working copy to the latest version of the master branch:
424 Afterwards, make the necessary changes for your bugfix/feature. Then, review the changes
425 using +git diff+ (you might want to enable colors in the diff using +git config diff.color auto+).
426 When you are definitely done, use +git commit -a+ to commit all changes you’ve made.
428 Then, use the following command to generate a patchfile which we can directly apply to
429 the branch, preserving your commit message and name:
431 -----------------------
432 git format-patch origin
433 -----------------------
435 Just send us the generated file via mail.