Hacking i3: How To
==================
-Michael Stapelberg <michael+i3@stapelberg.de>
-July 2011
+Michael Stapelberg <michael@i3wm.org>
+February 2013
This document is intended to be the first thing you read before looking and/or
touching i3’s source code. It should contain all important information to help
you understand why things are like they are. If it does not mention something
you find necessary, please do not hesitate to contact me.
+== Building i3
+
+You can build i3 like you build any other software package which uses autotools.
+Here’s a memory refresher:
+
+ $ autoreconf -fi
+ $ mkdir -p build && cd build
+ $ ../configure
+ $ make -j8
+
+(The autoreconf -fi step is unnecessary if you are building from a release tarball,
+ but shouldn’t hurt either.)
+
+=== Build system features
+
+* We use the AX_ENABLE_BUILDDIR macro to enforce builds happening in a separate
+ directory. This is a prerequisite for the AX_EXTEND_SRCDIR macro and building
+ in a separate directory is common practice anyway. In case this causes any
+ trouble when packaging i3 for your distribution, please open an issue.
+
+* “make check” runs the i3 testsuite. See docs/testsuite for details.
+
+* “make distcheck” (runs testsuite on “make dist” result, tiny bit quicker
+ feedback cycle than waiting for the travis build to catch the issue).
+
+* “make uninstall” (occasionally requested by users who compile from source)
+
+* “make” will build manpages/docs by default if the tools are installed.
+ Conversely, manpages/docs are not tried to be built for users who don’t want
+ to install all these dependencies to get started hacking on i3.
+
+* non-release builds will enable address sanitizer by default. Use the
+ --disable-sanitizers configure option to turn off all sanitizers, and see
+ --help for available sanitizers.
+
+* Support for pre-compiled headers (PCH) has been dropped for now in the
+ interest of simplicity. If you need support for PCH, please open an issue.
+
+* Coverage reports are now generated using “make check-code-coverage”, which
+ requires specifying --enable-code-coverage when calling configure.
+
+== Using git / sending patches
+
+For a short introduction into using git, see
+https://web.archive.org/web/20121024222556/http://www.spheredev.org/wiki/Git_for_the_lazy
+or, for more documentation, see https://git-scm.com/documentation
+
+Please talk to us before working on new features to see whether they will be
+accepted. A good way for this is to open an issue and asking for opinions on it.
+Even for accepted features, this can be a good way to refine an idea upfront. However,
+we don't want to see certain features in i3, e.g., switching window focus in an
+Alt+Tab like way.
+
+When working on bugfixes, please make sure you mention that you are working on
+it in the corresponding bug report at https://github.com/i3/i3/issues. In case
+there is no bug report yet, please create one.
+
+After you are done, please submit your work for review as a pull request at
+https://github.com/i3/i3.
+
+Do not send emails to the mailing list or any author directly, and don’t submit
+them in the bugtracker, since all reviews should be done in public at
+https://github.com/i3/i3. In order to make your review go as fast as possible, you
+could have a look at previous reviews and see what the common mistakes are.
+
+=== Which branch to use?
+
+Work on i3 generally happens in two branches: “master” and “next” (the latter
+being the default branch, the one that people get when they check out the git
+repository).
+
+The contents of “master” are always stable. That is, it contains the source code
+of the latest release, plus any bugfixes that were applied since that release.
+
+New features are only found in the “next” branch. Therefore, if you are working
+on a new feature, use the “next” branch. If you are working on a bugfix, use the
+“next” branch, too, but make sure your code also works on “master”.
+
== Window Managers
A window manager is not necessarily needed to run X, but it is usually used in
the first client of X) and manage them (reparent them, create window
decorations, etc.)
. When new windows are created, manage them
-. Handle the client’s `_WM_STATE` property, but only the `_WM_STATE_FULLSCREEN`
+. Handle the client’s `_WM_STATE` property, but only `_WM_STATE_FULLSCREEN` and
+ `_NET_WM_STATE_DEMANDS_ATTENTION`
. Handle the client’s `WM_NAME` property
. Handle the client’s size hints to display them proportionally
. Handle the client’s urgency hint
corresponds to tiling or stacking mode in i3. Therefore, why not let i3 do this
for you? Certainly, it’s faster than you could ever do it.
-The problem with most tiling window managers is that they are too unflexible.
+The problem with most tiling window managers is that they are too inflexible.
In my opinion, a window manager is just another tool, and similar to vim which
can edit all kinds of text files (like source code, HTML, …) and is not limited
to a specific file type, a window manager should not limit itself to a certain
layout (like dwm, awesome, …) but provide mechanisms for you to easily create
the layout you need at the moment.
-=== The layout table
-
-*********************************************************************************
-This section has not been updated for v4.0 yet, sorry! We wanted to release on
-time, but we will update this soon. Please talk to us on IRC if you need to
-know stuff *NOW* :).
-*********************************************************************************
+=== The layout tree
-/////////////////////////////////////////////////////////////////////////////////
-To accomplish flexible layouts, we decided to simply use a table. The table
-grows and shrinks as you need it. Each cell holds a container which then holds
-windows (see picture below). You can use different layouts for each container
-(default layout and stacking layout).
+The data structure which i3 uses to keep track of your windows is a tree. Every
+node in the tree is a container (type +Con+). Some containers represent actual
+windows (every container with a +window != NULL+), some represent split
+containers and a few have special purposes: they represent workspaces, outputs
+(like VGA1, LVDS1, …) or the X11 root window.
So, when you open a terminal and immediately open another one, they reside in
-the same container, in default layout. The layout table has exactly one column,
-one row and therefore one cell. When you move one of the terminals to the
-right, the table needs to grow. It will be expanded to two columns and one row.
-This enables you to have different layouts for each container. The table then
-looks like this:
-
-[width="15%",cols="^,^"]
-|========
-| T1 | T2
-|========
-
-When moving terminal 2 to the bottom, the table will be expanded again.
-
-[width="15%",cols="^,^"]
-|========
-| T1 |
-| | T2
-|========
-
-You can really think of the layout table like a traditional HTML table, if
-you’ve ever designed one. Especially col- and rowspan work similarly. Below,
-you see an example of colspan=2 for the first container (which has T1 as
-window).
-
-[width="15%",cols="^asciidoc"]
-|========
-| T1
-|
-[cols="^,^",frame="none"]
-!========
-! T2 ! T3
-!========
-|========
+the same split container, which uses the default layout. In case of an empty
+workspace, the split container we are talking about is the workspace.
-Furthermore, you can freely resize table cells.
-/////////////////////////////////////////////////////////////////////////////////
+To get an impression of how different layouts are represented, just play around
+and look at the data structures -- they are exposed as a JSON hash. See
+https://i3wm.org/docs/ipc.html#_tree_reply for documentation on that and an
+example.
== Files
doxygen-compatible comments (so if you want to get a bit more of the big
picture, either browse all header files or use doxygen if you prefer that).
-src/cfgparse.l::
-Contains the lexer for i3’s configuration file, written for +flex(1)+.
-
-src/cfgparse.y::
-Contains the parser for i3’s configuration file, written for +bison(1)+.
+src/config_parser.c::
+Contains a custom configuration parser. See src/command_parser.c for rationale
+ on why we use a custom parser.
src/click.c::
Contains all functions which handle mouse button clicks (right mouse button
clicks initiate resizing and thus are relatively complex).
-src/cmdparse.l::
-Contains the lexer for i3 commands, written for +flex(1)+.
-
-src/cmdparse.y::
-Contains the parser for i3 commands, written for +bison(1)+.
+src/command_parser.c::
+Contains a hand-written parser to parse commands (commands are what
+you bind on keys and what you can send to i3 using the IPC interface, like
+'move left' or 'workspace 4').
src/con.c::
Contains all functions which deal with containers directly (creating
src/config.c::
Contains all functions handling the configuration file (calling the parser
-(src/cfgparse.y) with the correct path, switching key bindings mode).
-
-src/debug.c::
-Contains debugging functions to print unhandled X events.
+src/config_parser.c) with the correct path, switching key bindings mode).
src/ewmh.c::
-iFunctions to get/set certain EWMH properties easily.
+Functions to get/set certain EWMH properties easily.
src/floating.c::
Contains functions for floating mode (mostly resizing/dragging).
Contains code for loading layouts from JSON files.
src/log.c::
-Handles the setting of loglevels, contains the logging functions.
+Contains the logging functions.
src/main.c::
Initializes the window manager.
src/resize.c::
Contains the functions to resize containers.
+src/restore_layout.c::
+Everything for restored containers that is not pure state parsing (which can be
+found in load_layout.c).
+
src/sighandler.c::
Handles +SIGSEGV+, +SIGABRT+ and +SIGFPE+ by showing a dialog that i3 crashed.
You can chose to let it dump core, to restart it in-place or to restart it
function, which was moved into its own file because it is so long.
src/util.c::
-Contains useful functions which are not really dependant on anything.
+Contains useful functions which are not really dependent on anything.
src/window.c::
Handlers to update X11 window properties like +WM_CLASS+, +_NET_WM_NAME+,
== Data structures
-*********************************************************************************
-This section has not been updated for v4.0 yet, sorry! We wanted to release on
-time, but we will update this soon. Please talk to us on IRC if you need to
-know stuff *NOW* :).
-*********************************************************************************
-
-/////////////////////////////////////////////////////////////////////////////////
See include/data.h for documented data structures. The most important ones are
explained right here.
+/////////////////////////////////////////////////////////////////////////////////
+// TODO: update image
+
image:bigpicture.png[The Big Picture]
/////////////////////////////////////////////////////////////////////////////////
So, the hierarchy is:
. *X11 root window*, the root container
-. *Virtual screens* (Screen 0 in this example)
+. *Output container* (LVDS1 in this example)
. *Content container* (there are also containers for dock windows)
. *Workspaces* (Workspace 1 in this example, with horizontal orientation)
. *Split container* (vertically split)
The data type is +Con+, in all cases.
-=== Virtual screens
+=== X11 root window
-A virtual screen (type `i3Screen`) is generated from the connected outputs
-obtained through RandR. The difference to the raw RandR outputs as seen
-when using +xrandr(1)+ is that it falls back to the lowest common resolution of
-the actual enabled outputs.
+The X11 root window is a single window per X11 display (a display is identified
+by +:0+ or +:1+ etc.). The root window is what you draw your background image
+on. It spans all the available outputs, e.g. +VGA1+ is a specific part of the
+root window and +LVDS1+ is a specific part of the root window.
+
+=== Output container
+
+Every active output obtained through RandR is represented by one output
+container. Outputs are considered active when a mode is configured (meaning
+something is actually displayed on the output) and the output is not a clone.
For example, if your notebook has a screen resolution of 1280x800 px and you
connect a video projector with a resolution of 1024x768 px, set it up in clone
-mode (+xrandr \--output VGA1 \--mode 1024x768 \--same-as LVDS1+), i3 will have
-one virtual screen.
+mode (+xrandr \--output VGA1 \--mode 1024x768 \--same-as LVDS1+), i3 will
+reduce the resolution to the lowest common resolution and disable one of the
+cloned outputs afterwards.
However, if you configure it using +xrandr \--output VGA1 \--mode 1024x768
-\--right-of LVDS1+, i3 will generate two virtual screens. For each virtual
-screen, a new workspace will be assigned. New workspaces are created on the
-screen you are currently on.
+\--right-of LVDS1+, i3 will set both outputs active. For each output, a new
+workspace will be assigned. New workspaces are created on the output you are
+currently on.
+
+=== Content container
+
+Each output has multiple children. Two of them are dock containers which hold
+dock clients. The other one is the content container, which holds the actual
+content (workspaces) of this output.
=== Workspace
A workspace is identified by its name. Basically, you could think of
workspaces as different desks in your office, if you like the desktop
-methaphor. They just contain different sets of windows and are completely
+metaphor. They just contain different sets of windows and are completely
separate of each other. Other window managers also call this ``Virtual
desktops''.
-=== The layout table
-
-*********************************************************************************
-This section has not been updated for v4.0 yet, sorry! We wanted to release on
-time, but we will update this soon. Please talk to us on IRC if you need to
-know stuff *NOW* :).
-*********************************************************************************
+=== Split container
-/////////////////////////////////////////////////////////////////////////////////
+A split container is a container which holds an arbitrary amount of split
+containers or X11 window containers. It has an orientation (horizontal or
+vertical) and a layout.
-Each workspace has a table, which is just a two-dimensional dynamic array
-containing Containers (see below). This table grows and shrinks as you need it
-(by moving windows to the right you can create a new column in the table, by
-moving them to the bottom you create a new row).
+Split containers (and X11 window containers, which are a subtype of split
+containers) can have different border styles.
-/////////////////////////////////////////////////////////////////////////////////
+=== X11 window container
-=== Container
-
-*********************************************************************************
-This section has not been updated for v4.0 yet, sorry! We wanted to release on
-time, but we will update this soon. Please talk to us on IRC if you need to
-know stuff *NOW* :).
-*********************************************************************************
-
-/////////////////////////////////////////////////////////////////////////////////
-
-A container is the content of a table’s cell. It holds an arbitrary amount of
-windows and has a specific layout (default layout, stack layout or tabbed
-layout). Containers can consume multiple table cells by modifying their
-colspan/rowspan attribute.
-
-/////////////////////////////////////////////////////////////////////////////////
-
-=== Client
-
-A client is x11-speak for a window.
+An X11 window container holds exactly one X11 window. These are the leaf nodes
+of the layout tree, they cannot have any children.
== List/queue macros
* The override_redirect must not be set. Windows with override_redirect shall
not be managed by a window manager
-Afterwards, i3 gets the intial geometry and reparents the window (see
+Afterwards, i3 gets the initial geometry and reparents the window (see
`reparent_window()`) if it wasn’t already managed.
Reparenting means that for each window which is reparented, a new window,
whether this window is a dock (`_NET_WM_WINDOW_TYPE_DOCK`), like dzen2 for
example. Docks are handled differently, they don’t have decorations and are not
assigned to a specific container. Instead, they are positioned at the bottom
-of the screen. To get the height which needs to be reserved for the window,
-the `_NET_WM_STRUT_PARTIAL` property is used.
+or top of the screen (in the appropriate dock area containers). To get the
+height which needs to be reserved for the window, the `_NET_WM_STRUT_PARTIAL`
+property is used.
Furthermore, the list of assignments (to other workspaces, which may be on
other screens) is checked. If the window matches one of the user’s criteria,
== What happens when an application is started?
-i3 does not care for applications. All it notices is when new windows are
+i3 does not care about applications. All it notices is when new windows are
mapped (see `src/handlers.c`, `handle_map_request()`). The window is then
reparented (see section "Manage windows").
== _NET_WM_STATE
-Only the _NET_WM_STATE_FULLSCREEN atom is handled. It calls
-``toggle_fullscreen()'' for the specific client which just configures the
-client to use the whole screen on which it currently is. Also, it is set as
-fullscreen_client for the i3Screen.
+Only the _NET_WM_STATE_FULLSCREEN and _NET_WM_STATE_DEMANDS_ATTENTION atoms
+are handled.
+
+The former calls ``toggle_fullscreen()'' for the specific client which just
+configures the client to use the whole screen on which it currently is.
+Also, it is set as fullscreen_client for the i3Screen.
+
+The latter is used to set, read and display urgency hints.
== WM_NAME
== Rendering (src/layout.c, render_layout() and render_container())
-*********************************************************************************
-This section has not been updated for v4.0 yet, sorry! We wanted to release on
-time, but we will update this soon. Please talk to us on IRC if you need to
-know stuff *NOW* :).
-*********************************************************************************
-
-/////////////////////////////////////////////////////////////////////////////////
-
-
-There are several entry points to rendering: `render_layout()`,
-`render_workspace()` and `render_container()`. The former one calls
-`render_workspace()` for every screen, which in turn will call
-`render_container()` for every container inside its layout table. Therefore, if
-you need to render only a single container, for example because a window was
-removed, added or changed its title, you should directly call
-render_container().
-
-Rendering consists of two steps: In the first one, in `render_workspace()`, each
-container gets its position (screen offset + offset in the table) and size
-(container's width times colspan/rowspan). Then, `render_container()` is called,
-which takes different approaches, depending on the mode the container is in:
-
-=== Common parts
-
-On the frame (the window which was created around the client’s window for the
-decorations), a black rectangle is drawn as a background for windows like
-MPlayer, which do not completely fit into the frame.
-
-=== Default mode
-
-Each clients gets the container’s width and an equal amount of height.
-
-=== Stack mode
-
-In stack mode, a window containing the decorations of all windows inside the
-container is placed at the top. The currently focused window is then given the
-whole remaining space.
-
-=== Tabbed mode
-
-Tabbed mode is like stack mode, except that the window decorations are drawn
-in one single line at the top of the container.
-
-=== Window decorations
+Rendering in i3 version 4 is the step which assigns the correct sizes for
+borders, decoration windows, child windows and the stacking order of all
+windows. In a separate step (+x_push_changes()+), these changes are pushed to
+X11.
+
+Keep in mind that all these properties (+rect+, +window_rect+ and +deco_rect+)
+are temporary, meaning they will be overwritten by calling +render_con+.
+Persistent position/size information is kept in +geometry+.
+
+The entry point for every rendering operation (except for the case of moving
+floating windows around) currently is +tree_render()+ which will re-render
+everything that’s necessary (for every output, only the currently displayed
+workspace is rendered). This behavior is expected to change in the future,
+since for a lot of updates, re-rendering everything is not actually necessary.
+Focus was on getting it working correct, not getting it work very fast.
+
+What +tree_render()+ actually does is calling +render_con()+ on the root
+container and then pushing the changes to X11. The following sections talk
+about the different rendering steps, in the order of "top of the tree" (root
+container) to the bottom.
+
+=== Rendering the root container
+
+The i3 root container (`con->type == CT_ROOT`) represents the X11 root window.
+It contains one child container for every output (like LVDS1, VGA1, …), which
+is available on your computer.
+
+Rendering the root will first render all tiling windows and then all floating
+windows. This is necessary because a floating window can be positioned in such
+a way that it is visible on two different outputs. Therefore, by first
+rendering all the tiling windows (of all outputs), we make sure that floating
+windows can never be obscured by tiling windows.
+
+Essentially, though, this code path will just call +render_con()+ for every
+output and +x_raise_con(); render_con()+ for every floating window.
+
+In the special case of having a "global fullscreen" window (fullscreen mode
+spanning all outputs), a shortcut is taken and +x_raise_con(); render_con()+ is
+only called for the global fullscreen window.
+
+=== Rendering an output
+
+Output containers (`con->layout == L_OUTPUT`) represent a hardware output like
+LVDS1, VGA1, etc. An output container has three children (at the moment): One
+content container (having workspaces as children) and the top/bottom dock area
+containers.
+
+The rendering happens in the function +render_l_output()+ in the following
+steps:
+
+1. Find the content container (`con->type == CT_CON`)
+2. Get the currently visible workspace (+con_get_fullscreen_con(content,
+ CF_OUTPUT)+).
+3. If there is a fullscreened window on that workspace, directly render it and
+ return, thus ignoring the dock areas.
+4. Sum up the space used by all the dock windows (they have a variable height
+ only).
+5. Set the workspace rects (x/y/width/height) based on the position of the
+ output (stored in `con->rect`) and the usable space
+ (`con->rect.{width,height}` without the space used for dock windows).
+6. Recursively raise and render the output’s child containers (meaning dock
+ area containers and the content container).
+
+=== Rendering a workspace or split container
+
+From here on, there really is no difference anymore. All containers are of
+`con->type == CT_CON` (whether workspace or split container) and some of them
+have a `con->window`, meaning they represent an actual window instead of a
+split container.
+
+==== Default layout
+
+In default layout, containers are placed horizontally or vertically next to
+each other (depending on the `con->orientation`). If a child is a leaf node (as
+opposed to a split container) and has border style "normal", appropriate space
+will be reserved for its window decoration.
+
+==== Stacked layout
+
+In stacked layout, only the focused window is actually shown (this is achieved
+by calling +x_raise_con()+ in reverse focus order at the end of +render_con()+).
+
+The available space for the focused window is the size of the container minus
+the height of the window decoration for all windows inside this stacked
+container.
-The window decorations consist of a rectangle in the appropriate color (depends
-on whether this window is the currently focused one, the last focused one in a
-not focused container or not focused at all) forming the background.
-Afterwards, two lighter lines are drawn and the last step is drawing the
-window’s title (see WM_NAME) onto it.
+If border style is "1pixel" or "none", no window decoration height will be
+reserved (or displayed later on), unless there is more than one window inside
+the stacked container.
+
+==== Tabbed layout
+
+Tabbed layout works precisely like stacked layout, but the window decoration
+position/size is different: They are placed next to each other on a single line
+(fixed height).
+
+==== Dock area layout
+
+This is a special case. Users cannot choose the dock area layout, but it will be
+set for the dock area containers. In the dockarea layout (at the moment!),
+windows will be placed above each other.
+
+=== Rendering a window
+
+A window’s size and position will be determined in the following way:
+
+1. Subtract the border if border style is not "none" (but "normal" or "1pixel").
+2. Subtract the X11 border, if the window has an X11 border > 0.
+3. Obey the aspect ratio of the window (think MPlayer).
+4. Obey the height- and width-increments of the window (think terminal emulator
+ which can only be resized in one-line or one-character steps).
+
+== Pushing updates to X11 / Drawing
+
+A big problem with i3 before version 4 was that we just sent requests to X11
+anywhere in the source code. This was bad because nobody could understand the
+entirety of our interaction with X11, it lead to subtle bugs and a lot of edge
+cases which we had to consider all over again.
+
+Therefore, since version 4, we have a single file, +src/x.c+, which is
+responsible for repeatedly transferring parts of our tree datastructure to X11.
+
++src/x.c+ consists of multiple parts:
+
+1. The state pushing: +x_push_changes()+, which calls +x_push_node()+.
+2. State modification functions: +x_con_init+, +x_reinit+,
+ +x_reparent_child+, +x_move_win+, +x_con_kill+, +x_raise_con+, +x_set_name+
+ and +x_set_warp_to+.
+3. Expose event handling (drawing decorations): +x_deco_recurse()+ and
+ +x_draw_decoration()+.
+
+=== Pushing state to X11
+
+In general, the function +x_push_changes+ should be called to push state
+changes. Only when the scope of the state change is clearly defined (for
+example only the title of a window) and its impact is known beforehand, one can
+optimize this and call +x_push_node+ on the appropriate con directly.
+
++x_push_changes+ works in the following steps:
+
+1. Clear the eventmask for all mapped windows. This leads to not getting
+ useless ConfigureNotify or EnterNotify events which are caused by our
+ requests. In general, we only want to handle user input.
+2. Stack windows above each other, in reverse stack order (starting with the
+ most obscured/bottom window). This is relevant for floating windows which
+ can overlap each other, but also for tiling windows in stacked or tabbed
+ containers. We also update the +_NET_CLIENT_LIST_STACKING+ hint which is
+ necessary for tab drag and drop in Chromium.
+3. +x_push_node+ will be called for the root container, recursively calling
+ itself for the container’s children. This function actually pushes the
+ state, see the next paragraph.
+4. If the pointer needs to be warped to a different position (for example when
+ changing focus to a different output), it will be warped now.
+5. The eventmask is restored for all mapped windows.
+6. Window decorations will be rendered by calling +x_deco_recurse+ on the root
+ container, which then recursively calls itself for the children.
+7. If the input focus needs to be changed (because the user focused a different
+ window), it will be updated now.
+8. +x_push_node_unmaps+ will be called for the root container. This function
+ only pushes UnmapWindow requests. Separating the state pushing is necessary
+ to handle fullscreen windows (and workspace switches) in a smooth fashion:
+ The newly visible windows should be visible before the old windows are
+ unmapped.
+
++x_push_node+ works in the following steps:
+
+1. Update the window’s +WM_NAME+, if changed (the +WM_NAME+ is set on i3
+ containers mainly for debugging purposes).
+2. Reparents a child window into the i3 container if the container was created
+ for a specific managed window.
+3. If the size/position of the i3 container changed (due to opening a new
+ window or switching layouts for example), the window will be reconfigured.
+ Also, the pixmap which is used to draw the window decoration/border on is
+ reconfigured (pixmaps are size-dependent).
+4. Size/position for the child window is adjusted.
+5. The i3 container is mapped if it should be visible and was not yet mapped.
+ When mapping, +WM_STATE+ is set to +WM_STATE_NORMAL+. Also, the eventmask of
+ the child window is updated and the i3 container’s contents are copied from
+ the pixmap.
+6. +x_push_node+ is called recursively for all children of the current
+ container.
+
++x_push_node_unmaps+ handles the remaining case of an i3 container being
+unmapped if it should not be visible anymore. +WM_STATE+ will be set to
++WM_STATE_WITHDRAWN+.
+
+
+=== Drawing window decorations/borders/backgrounds
+
++x_draw_decoration+ draws window decorations. It is run for every leaf
+container (representing an actual X11 window) and for every non-leaf container
+which is in a stacked/tabbed container (because stacked/tabbed containers
+display a window decoration for split containers, which consists of a representation
+of the child container's names.
+
+Then, parameters are collected to be able to determine whether this decoration
+drawing is actually necessary or was already done. This saves a substantial
+number of redraws (depending on your workload, but far over 50%).
+
+Assuming that we need to draw this decoration, we start by filling the empty
+space around the child window (think of MPlayer with a specific aspect ratio)
+in the user-configured client background color.
+
+Afterwards, we draw the appropriate border (in case of border styles "normal"
+and "1pixel") and the top bar (in case of border style "normal").
+
+The last step is drawing the window title on the top bar.
-=== Fullscreen windows
-For fullscreen windows, the `rect` (x, y, width, height) is not changed to
-allow the client to easily go back to its previous position. Instead,
-fullscreen windows are skipped when rendering.
+/////////////////////////////////////////////////////////////////////////////////
-=== Resizing containers
+== Resizing containers
By clicking and dragging the border of a container, you can resize the whole
column (respectively row) which this container is in. This is necessary to keep
/////////////////////////////////////////////////////////////////////////////////
-== User commands / commandmode (src/cmdparse.{l,y})
-
-*********************************************************************************
-This section has not been updated for v4.0 yet, sorry! We wanted to release on
-time, but we will update this soon. Please talk to us on IRC if you need to
-know stuff *NOW* :).
-*********************************************************************************
-
-/////////////////////////////////////////////////////////////////////////////////
-
-
-Like in vim, you can control i3 using commands. They are intended to be a
-powerful alternative to lots of shortcuts, because they can be combined. There
-are a few special commands, which are the following:
-
-exec <command>::
-Starts the given command by passing it to `/bin/sh`.
-
-restart::
-Restarts i3 by executing `argv[0]` (the path with which you started i3) without
-forking.
-
-w::
-"With". This is used to select a bunch of windows. Currently, only selecting
-the whole container in which the window is in, is supported by specifying "w".
-
-f, s, d::
-Toggle fullscreen, stacking, default mode for the current window/container.
-
-The other commands are to be combined with a direction. The directions are h,
-j, k and l, like in vim (h = left, j = down, k = up, l = right). When you just
-specify the direction keys, i3 will move the focus in that direction. You can
-provide "m" or "s" before the direction to move a window respectively or snap.
-
-/////////////////////////////////////////////////////////////////////////////////
+== User commands (parser-specs/commands.spec)
+
+In the configuration file and when using i3 interactively (with +i3-msg+, for
+example), you use commands to make i3 do things, like focus a different window,
+set a window to fullscreen, and so on. An example command is +floating enable+,
+which enables floating mode for the currently focused window. See the
+appropriate section in the link:userguide.html[User’s Guide] for a reference of
+all commands.
+
+In earlier versions of i3, interpreting these commands was done using lex and
+yacc, but experience has shown that lex and yacc are not well suited for our
+command language. Therefore, starting from version 4.2, we use a custom parser
+for user commands and the configuration file.
+The input specification for this parser can be found in the file
++parser-specs/*.spec+. Should you happen to use Vim as an editor, use
+:source parser-specs/highlighting.vim to get syntax highlighting for this file
+(highlighting files for other editors are welcome).
+
+.Excerpt from commands.spec
+-----------------------------------------------------------------------
+state INITIAL:
+ '[' -> call cmd_criteria_init(); CRITERIA
+ 'move' -> MOVE
+ 'exec' -> EXEC
+ 'workspace' -> WORKSPACE
+ 'exit' -> call cmd_exit()
+ 'restart' -> call cmd_restart()
+ 'reload' -> call cmd_reload()
+-----------------------------------------------------------------------
+
+The input specification is written in an extremely simple format. The
+specification is then converted into C code by the Perl script
+generate-commands-parser.pl (the output file names begin with GENERATED and the
+files are stored in the +include+ directory). The parser implementation
++src/commands_parser.c+ includes the generated C code at compile-time.
+
+The above excerpt from commands.spec illustrates nearly all features of our
+specification format: You describe different states and what can happen within
+each state. State names are all-caps; the state in the above excerpt is called
+INITIAL. A list of tokens and their actions (separated by an ASCII arrow)
+follows. In the excerpt, all tokens are literals, that is, simple text strings
+which will be compared with the input. An action is either the name of a state
+in which the parser will transition into, or the keyword 'call', followed by
+the name of a function (and optionally a state).
+
+=== Example: The WORKSPACE state
+
+Let’s have a look at the WORKSPACE state, which is a good example of all
+features. This is its definition:
+
+.WORKSPACE state (commands.spec)
+----------------------------------------------------------------
+# workspace next|prev|next_on_output|prev_on_output
+# workspace back_and_forth
+# workspace <name>
+# workspace number <number>
+state WORKSPACE:
+ direction = 'next_on_output', 'prev_on_output', 'next', 'prev'
+ -> call cmd_workspace($direction)
+ 'back_and_forth'
+ -> call cmd_workspace_back_and_forth()
+ 'number'
+ -> WORKSPACE_NUMBER
+ workspace = string
+ -> call cmd_workspace_name($workspace)
+----------------------------------------------------------------
+
+As you can see from the commands, there are multiple different valid variants
+of the workspace command:
+
+workspace <direction>::
+ The word 'workspace' can be followed by any of the tokens 'next',
+ 'prev', 'next_on_output' or 'prev_on_output'. This command will
+ switch to the next or previous workspace (optionally on the same
+ output). +
+ There is one function called +cmd_workspace+, which is defined
+ in +src/commands.c+. It will handle this kind of command. To know which
+ direction was specified, the direction token is stored on the stack
+ with the name "direction", which is what the "direction = " means in
+ the beginning. +
+
+NOTE: Note that you can specify multiple literals in the same line. This has
+ exactly the same effect as if you specified `direction =
+ 'next_on_output' -> call cmd_workspace($direction)` and so forth. +
+
+NOTE: Also note that the order of literals is important here: If 'next' were
+ ordered before 'next_on_output', then 'next_on_output' would never
+ match.
+
+workspace back_and_forth::
+ This is a very simple case: When the literal 'back_and_forth' is found
+ in the input, the function +cmd_workspace_back_and_forth+ will be
+ called without parameters and the parser will return to the INITIAL
+ state (since no other state was specified).
+workspace <name>::
+ In this case, the workspace command is followed by an arbitrary string,
+ possibly in quotes, for example "workspace 3" or "workspace bleh". +
+ This is the first time that the token is actually not a literal (not in
+ single quotes), but just called string. Other possible tokens are word
+ (the same as string, but stops matching at a whitespace) and end
+ (matches the end of the input).
+workspace number <number>::
+ The workspace command has to be followed by the keyword +number+. It
+ then transitions into the state +WORKSPACE_NUMBER+, where the actual
+ parameter will be read.
+
+=== Introducing a new command
+
+The following steps have to be taken in order to properly introduce a new
+command (or possibly extend an existing command):
+
+1. Define a function beginning with +cmd_+ in the file +src/commands.c+. Copy
+ the prototype of an existing function.
+2. After adding a comment on what the function does, copy the comment and
+ function definition to +include/commands.h+. Make the comment in the header
+ file use double asterisks to make doxygen pick it up.
+3. Write a test case (or extend an existing test case) for your feature, see
+ link:testsuite.html[i3 testsuite]. For now, it is sufficient to simply call
+ your command in all the various possible ways.
+4. Extend the parser specification in +parser-specs/commands.spec+. Run the
+ testsuite and see if your new function gets called with the appropriate
+ arguments for the appropriate input.
+5. Actually implement the feature.
+6. Document the feature in the link:userguide.html[User’s Guide].
== Moving containers
Afterwards, +con_focus+ will be called to fix the focus stack and the tree will
be flattened.
-=== Case 3: Moving to non-existant top/bottom
+=== Case 3: Moving to non-existent top/bottom
Like in case 1, the reference layout for this case is a single workspace in
horizontal orientation with two containers on it. Focus is on the left
Now, +con_focus+ will be called to fix the focus stack and the tree will be
flattened.
-=== Case 4: Moving to existant top/bottom
+=== Case 4: Moving to existent top/bottom
The reference layout for this case is a vertical workspace with two containers.
The bottom one is a h-split containing two containers (1 and 2). Focus is on
leads to code which looks like it works fine but which does not work under
certain conditions.
-== Using git / sending patches
-
-For a short introduction into using git, see
-http://www.spheredev.org/wiki/Git_for_the_lazy or, for more documentation, see
-http://git-scm.com/documentation
-
-When you want to send a patch because you fixed a bug or implemented a cool
-feature (please talk to us before working on features to see whether they are
-maybe already implemented, not possible for some some reason, or don’t fit
-into the concept), please use git to create a patchfile.
-
-First of all, update your working copy to the latest version of the master
-branch:
-
---------
-git pull
---------
-
-Afterwards, make the necessary changes for your bugfix/feature. Then, review
-the changes using +git diff+ (you might want to enable colors in the diff using
-+git config diff.color auto+). When you are definitely done, use +git commit
--a+ to commit all changes you’ve made.
-
-Then, use the following command to generate a patchfile which we can directly
-apply to the branch, preserving your commit message and name:
-
------------------------
-git format-patch origin
------------------------
-
-Just send us the generated file via email.
+* Forgetting to call `floating_fix_coordinates(con, old_rect, new_rect)` after
+ moving workspaces across outputs. Coordinates for floating containers are
+ not relative to workspace boundaries, so you must correct their coordinates
+ or those containers will show up in the wrong workspace or not at all.
+
+== Thought experiments
+
+In this section, we collect thought experiments, so that we don’t forget our
+thoughts about specific topics. They are not necessary to get into hacking i3,
+but if you are interested in one of the topics they cover, you should read them
+before asking us why things are the way they are or why we don’t implement
+things.
+
+=== Using cgroups per workspace
+
+cgroups (control groups) are a linux-only feature which provides the ability to
+group multiple processes. For each group, you can individually set resource
+limits, like allowed memory usage. Furthermore, and more importantly for our
+purposes, they serve as a namespace, a label which you can attach to processes
+and their children.
+
+One interesting use for cgroups is having one cgroup per workspace (or
+container, doesn’t really matter). That way, you could set different priorities
+and have a workspace for important stuff (say, writing a LaTeX document or
+programming) and a workspace for unimportant background stuff (say,
+JDownloader). Both tasks can obviously consume a lot of I/O resources, but in
+this example it doesn’t really matter if JDownloader unpacks the download a
+minute earlier or not. However, your compiler should work as fast as possible.
+Having one cgroup per workspace, you would assign more resources to the
+programming workspace.
+
+Another interesting feature is that an inherent problem of the workspace
+concept could be solved by using cgroups: When starting an application on
+workspace 1, then switching to workspace 2, you will get the application’s
+window(s) on workspace 2 instead of the one you started it on. This is because
+the window manager does not have any mapping between the process it starts (or
+gets started in any way) and the window(s) which appear.
+
+Imagine for example using dmenu: The user starts dmenu by pressing Mod+d, dmenu
+gets started with PID 3390. The user then decides to launch Firefox, which
+takes a long time. So they enter firefox into dmenu and press enter. Firefox
+gets started with PID 4001. When it finally finishes loading, it creates an X11
+window and uses MapWindow to make it visible. This is the first time i3
+actually gets in touch with Firefox. It decides to map the window, but it has
+no way of knowing that this window (even though it has the _NET_WM_PID property
+set to 4001) belongs to the dmenu the user started before.
+
+How do cgroups help with this? Well, when pressing Mod+d to launch dmenu, i3
+would create a new cgroup, let’s call it i3-3390-1. It launches dmenu in that
+cgroup, which gets PID 3390. As before, the user enters firefox and Firefox
+gets launched with PID 4001. This time, though, the Firefox process with PID
+4001 is *also* member of the cgroup i3-3390-1 (because fork()ing in a cgroup
+retains the cgroup property). Therefore, when mapping the window, i3 can look
+up in which cgroup the process is and can establish a mapping between the
+workspace and the window.
+
+There are multiple problems with this approach:
+
+. Every application has to properly set +_NET_WM_PID+. This is acceptable and
+ patches can be written for the few applications which don’t set the hint yet.
+. It does only work on Linux, since cgroups are a Linux-only feature. Again,
+ this is acceptable.
+. The main problem is that some applications create X11 windows completely
+ independent of UNIX processes. An example for this is Chromium (or
+ gnome-terminal), which, when being started a second time, communicates with
+ the first process and lets the first process open a new window. Therefore, if
+ you have a Chromium window on workspace 2 and you are currently working on
+ workspace 3, starting +chromium+ does not lead to the desired result (the
+ window will open on workspace 2).
+
+Therefore, my conclusion is that the only proper way of fixing the "window gets
+opened on the wrong workspace" problem is in the application itself. Most
+modern applications support freedesktop startup-notifications which can be
+used for this.
projects / i3 / i3 / blobdiff