4. Client to Window Manager Communication

In general, these conventions are somewhat complex and will undoubtedly change as new window management paradigms are developed. Thus, there is a strong bias toward defining only those conventions that are essential and that apply generally to all window management paradigms. Clients designed to run with a particular window manager can easily define private protocols to add to these conventions, but they must be aware that their users may decide to run some other window manager no matter how much the designers of the private protocol are convinced that they have seen the "one true light" of user interfaces.

It is a principle of these conventions that a general client should neither know nor care which window manager is running or, indeed, if one is running at all. The conventions do not support all client functions without a window manager running; for example, the concept of Iconic is not directly supported by clients. If no window manager is running, the concept of Iconic does not apply. A goal of the conventions is to make it possible to kill and restart window managers without loss of functionality.

Each window manager will implement a particular window management policy; the choice of an appropriate window management policy for the user's circumstances is not one for an individual client to make but will be made by the user or the user's system administrator. This does not exclude the possibility of writing clients that use a private protocol to restrict themselves to operating only under a specific window manager. Rather, it merely ensures that no claim of general utility is made for such programs.

For example, the claim is often made: "The client I'm writing is important, and it needs to be on top." Perhaps it is important when it is being run in earnest, and it should then be run under the control of a window manager that recognizes "important" windows through some private protocol and ensures that they are on top. However, imagine, for example, that the "important" client is being debugged. Then, ensuring that it is always on top is no longer the appropriate window management policy, and it should be run under a window manager that allows other windows (for example, the debugger) to appear on top.

4.1. Client's Actions

• Hinting to the window manager about the resources they would like to obtain
• Cooperating with the window manager by accepting the resources they are allocated even if they are not those requested
• Being prepared for resource allocations to change at any time

4.1.1. Creating a Top-Level Window

A client usually would expect to create its top-level windows as children of one or more of the root windows by using some boilerplate like the following:

win = XCreateSimpleWindow(dpy, DefaultRootWindow(dpy), xsh.x, xsh.y,
	xsh.width, xsh.height, bw, bd, bg);

If a particular one of the root windows was required, however, it could use something like the following:

win = XCreateSimpleWindow(dpy, DefaultRootWindow(dpy), xsh.x, xsh.y,
	xsh.width, xsh.height, bw, bd, bg);

Ideally, it should be possible to override the choice of a root window and allow clients (including window managers) to treat a nonroot window as a pseudo-root. This would allow, for example, the testing of window managers and the use of application-specific window managers to control the subwindows owned by the members of a related suite of clients. Doing so properly requires an extension, the design of which is under study.

From the client's point of view, the window manager will regard its top-level window as being in one of three states:

• Normal
• Iconic
• Withdrawn

4.1.2. Client Properties

The window manager will examine the contents of these properties when the window makes the transition from the Withdrawn state and will monitor some properties for changes while the window is in the Iconic or Normal state. When the client changes one of these properties, it must use Replace mode to overwrite the entire property with new data; the window manager will retain no memory of the old value of the property. All fields of the property must be set to suitable values in a single Replace mode ChangeProperty request. This ensures that the full contents of the property will be available to a new window manager if the existing one crashes, if it is shut down and restarted, or if the session needs to be shut down and restarted by the session manager.

Convention

Clients writing or rewriting window manager properties must ensure that the entire content of each property remains valid at all times.

Some of these properties may contain the IDs of resources, such as windows or pixmaps. Clients should ensure that these resources exist for at least as long as the window on which the property resides.

If these properties are longer than expected, clients should ignore the remainder of the property. Extending these properties is reserved to the X Consortium; private extensions to them are forbidden. Private additional communication between clients and window managers should take place using separate properties. The only exception to this rule is the WM_PROTOCOLS property, which may be of arbitrary length and which may contain atoms representing private protocols; see section 4.1.2.7.

The next sections describe each of the properties the clients need to set, in turn. They are summarized in the table in section 4.4.

4.1.2.1. WM_NAME Property

The encoding used for this string (and all other uninterpreted string properties) is implied by the type of the property. The type atoms to be used for this purpose are described in section 2.7.1.

Window managers are expected to make an effort to display this information. Simply ignoring WM_NAME is not acceptable behavior. Clients can assume that at least the first part of this string is visible to the user and that if the information is not visible to the user, it is because the user has taken an explicit action to make it invisible.

On the other hand, there is no guarantee that the user can see the WM_NAME string even if the window manager supports window headlines. The user may have placed the headline off-screen or have covered it by other windows. WM_NAME should not be used for application-critical information or to announce asynchronous changes of an application's state that require timely user response. The expected uses are to permit the user to identify one of a number of instances of the same client and to provide the user with noncritical state information.

Even window managers that support headline bars will place some limit on the length of the WM_NAME string that can be visible; brevity here will pay dividends.

4.1.2.2. WM_ICON_NAME Property

Clients should not attempt to display this string in their icon pixmaps or windows; rather, they should rely on the window manager to do so.

4.1.2.3. WM_NORMAL_HINTS Property

The WM_SIZE_HINTS.flags bit definitions are as follows:

Name	Value	Field
USPosition	1	User-specified x, y
USSize	2	User-specified width, height
PPosition	4	Program-specified position
PSizeT}	8	Program-specified size
PMinSize	16	Program-specified minimum size
PMaxSize	32	Program-specified maximum size
PResizeInc	64	Program-specified resize increments
PAspect	128	Program-specified min and max aspect ratios
PBaseSize	256	Program-specified base size
PWinGravity	512	Program-specified window gravity

To indicate that the size and position of the window (when a transition from the Withdrawn state occurs) was specified by the user, the client should set the USPosition and USSize flags, which allow a window manager to know that the user specifically asked where the window should be placed or how the window should be sized and that further interaction is superfluous. To indicate that it was specified by the client without any user involvement, the client should set PPosition and PSize .

The size specifiers refer to the width and height of the client's window excluding borders.

The win_gravity may be any of the values specified for WINGRAVITY in the core protocol except for Unmap : NorthWest (1), North (2), NorthEast (3), West (4), Center (5), East (6), SouthWest (7), South (8), and SouthEast (9). It specifies how and whether the client window wants to be shifted to make room for the window manager frame.

If the win_gravity is Static , the window manager frame is positioned so that the inside border of the client window inside the frame is in the same position on the screen as it was when the client requested the transition from Withdrawn state. Other values of win_gravity specify a window reference point. For NorthWest , NorthEast , SouthWest , and SouthEast the reference point is the specified outer corner of the window (on the outside border edge). For North , South , East , and West the reference point is the center of the specified outer edge of the window border. For Center the reference point is the center of the window. The reference point of the window manager frame is placed at the location on the screen where the reference point of the client window was when the client requested the transition from Withdrawn state.

The min_width and min_height elements specify the minimum size that the window can be for the client to be useful. The max_width and max_height elements specify the maximum size. The base_width and base_height elements in conjunction with width_inc and height_inc define an arithmetic progression of preferred window widths and heights for nonnegative integers i and j:

$width\; =\; base\_width\; +\; (i\; \times \; width\_inc)$
height = base_height + (j × height_inc)

Window managers are encouraged to use i and j instead of width and height in reporting window sizes to users. If a base size is not provided, the minimum size is to be used in its place and vice versa.

The min_aspect and max_aspect fields are fractions with the numerator first and the denominator second, and they allow a client to specify the range of aspect ratios it prefers. Window managers that honor aspect ratios should take into account the base size in determining the preferred window size. If a base size is provided along with the aspect ratio fields, the base size should be subtracted from the window size prior to checking that the aspect ratio falls in range. If a base size is not provided, nothing should be subtracted from the window size. (The minimum size is not to be used in place of the base size for this purpose.)

4.1.2.4. WM_HINTS Property

The WM_HINTS.flags bit definitions are as follows:

Name	Value	Field
InputHint	1	input
StateHint	2	initial_state
IconPixmapHint	4	icon_pixmap
IconWindowHint	8	icon_window
IconPositionHint	16	icon_x & icon_y
IconMaskHint	32	icon_mask
WindowGroupHint	64	window_group
MessageHint	128	(this bit is obsolete)
UrgencyHint	256	urgency

Window managers are free to assume convenient values for all fields of the WM_HINTS property if a window is mapped without one.

The input field is used to communicate to the window manager the input focus model used by the client (see section 4.1.7).

Clients with the Globally Active and No Input models should set the input flag to False . Clients with the Passive and Locally Active models should set the input flag to True .

From the client's point of view, the window manager will regard the client's top-level window as being in one of three states:

• Normal
• Iconic
• Withdrawn

The value of the initial_state field determines the state the client wishes to be in at the time the top-level window is mapped from the Withdrawn state, as shown in the following table:

State	Value	Comments
NormalState	1	The window is visible
IconicState	3	The icon is visible

The icon_pixmap field may specify a pixmap to be used as an icon. This pixmap should be:

• One of the sizes specified in the WM_ICON_SIZE property on the root if it exists (see section 4.1.3.2).
• 1-bit deep. The window manager will select, through the defaults database, suitable background (for the 0 bits) and foreground (for the 1 bits) colors. These defaults can, of course, specify different colors for the icons of different clients.

The icon_window field is the ID of a window the client wants used as its icon. Most, but not all, window managers will support icon windows. Those that do not are likely to have a user interface in which small windows that behave like icons are completely inappropriate. Clients should not attempt to remedy the omission by working around it.

Clients that need more capabilities from the icons than a simple two-color bitmap should use icon windows. Rules for clients that do are set out in section 4.1.9.

The (icon_x,icon_y) coordinate is a hint to the window manager as to where it should position the icon. The policies of the window manager control the positioning of icons, so clients should not depend on attention being paid to this hint.

The window_group field lets the client specify that this window belongs to a group of windows. An example is a single client manipulating multiple children of the root window.

Conventions

1. The window_group field should be set to the ID of the group leader. The window group leader may be a window that exists only for that purpose; a placeholder group leader of this kind would never be mapped either by the client or by the window manager.
2. The properties of the window group leader are those for the group as a whole (for example, the icon to be shown when the entire group is iconified).

Window managers may provide facilities for manipulating the group as a whole. Clients, at present, have no way to operate on the group as a whole.

The messages bit, if set in the flags field, indicates that the client is using an obsolete window manager communication protocol,¹¹ rather than the WM_PROTOCOLS mechanism of section 4.1.2.7.

The UrgencyHint flag, if set in the flags field, indicates that the client deems the window contents to be urgent, requiring the timely response of the user. The window manager must make some effort to draw the user's attention to this window while this flag is set. The window manager must also monitor the state of this flag for the entire time the window is in the Normal or Iconic state and must take appropriate action when the state of the flag changes. The flag is otherwise independent of the window's state; in particular, the window manager is not required to deiconify the window if the client sets the flag on an Iconic window. Clients must provide some means by which the user can cause the UrgencyHint flag to be set to zero or the window to be withdrawn. The user's action can either mitigate the actual condition that made the window urgent, or it can merely shut off the alarm.

Rationale

This mechanism is useful for alarm dialog boxes or reminder windows, in cases where mapping the window is not enough (e.g. in the presence of multi-workspace or virtual desktop window managers), and where using an override-redirect window is too intrusive. For example, the window manager may attract attention to an urgent window by adding an indicator to its title bar or its icon. Window managers may also take additional action for a window that is newly urgent, such as by flashing its icon (if the window is iconic) or by raising it to the top of the stack.

4.1.2.5. WM_CLASS Property

The two strings, respectively, are:

• A string that names the particular instance of the application to which the client that owns this window belongs. Resources that are specified by instance name override any resources that are specified by class name. Instance names can be specified by the user in an operating-system specific manner. On POSIX-conformant systems, the following conventions are used:
  • If "-name NAME" is given on the command line, NAME is used as the instance name.
  • Otherwise, if the environment variable RESOURCE_NAME is set, its value will be used as the instance name.
  • Otherwise, the trailing part of the name used to invoke the program (argv[0] stripped of any directory names) is used as the instance name.
• A string that names the general class of applications to which the client that owns this window belongs. Resources that are specified by class apply to all applications that have the same class name. Class names are specified by the application writer. Examples of commonly used class names include: "Emacs", "XTerm", "XClock", "XLoad", and so on.

4.1.2.6. WM_TRANSIENT_FOR Property

It is important not to confuse WM_TRANSIENT_FOR with override-redirect. WM_TRANSIENT_FOR should be used in those cases where the pointer is not grabbed while the window is mapped (in other words, if other windows are allowed to be active while the transient is up). If other windows must be prevented from processing input (for example, when implementing pop-up menus), use override-redirect and grab the pointer while the window is mapped.

4.1.2.7. WM_PROTOCOLS Property

All the protocols in which a client can volunteer to take part involve the window manager sending the client a ClientMessage event and the client taking appropriate action. For details of the contents of the event, see section 4.2.8. In each case, the protocol transactions are initiated by the window manager.

The WM_PROTOCOLS property is not required. If it is not present, the client does not want to participate in any window manager protocols.

The X Consortium will maintain a registry of protocols to avoid collisions in the name space. The following table lists the protocols that have been defined to date.

Protocol	Section	Purpose
WM_TAKE_FOCUS	4.1.7	Assignment of input focus
WM_SAVE_YOURSELF	Appendix C	Save client state request (deprecated)
WM_DELETE_WINDOW	4.2.8.1	Request to delete top-level window

It is expected that this table will grow over time.

4.1.2.8. WM_COLORMAP_WINDOWS Property

4.1.2.9. WM_CLIENT_MACHINE Property

4.1.3. Window Manager Properties

4.1.3.1. WM_STATE Property

Some clients (such as xprop) will ask the user to click over a window on which the program is to operate. Typically, the intent is for this to be a top-level window. To find a top-level window, clients should search the window hierarchy beneath the selected location for a window with the WM_STATE property. This search must be recursive in order to cover all window manager reparenting possibilities. If no window with a WM_STATE property is found, it is recommended that programs use a mapped child-of-root window if one is present beneath the selected location.

The contents of the WM_STATE property are defined as follows:

Field	Type	Comments
state	CARD32	(see the next table)
icon	WINDOW	ID of icon window

The following table lists the WM_STATE.state values:

State	Value
WithdrawnState	0
NormalState	1
IconicState	3

Adding other fields to this property is reserved to the X Consortium. Values for the state field other than those defined in the above table are reserved for use by X Consortium.

The state field describes the window manager's idea of the state the window is in, which may not match the client's idea as expressed in the initial_state field of the WM_HINTS property (for example, if the user has asked the window manager to iconify the window). If it is NormalState , the window manager believes the client should be animating its window. If it is IconicState , the client should animate its icon window. In either state, clients should be prepared to handle exposure events from either window.

When the window is withdrawn, the window manager will either change the state field's value to WithdrawnState or it will remove the WM_STATE property entirely.

The icon field should contain the window ID of the window that the window manager uses as the icon for the window on which this property is set. If no such window exists, the icon field should be None . Note that this window could be but is not necessarily the same window as the icon window that the client may have specified in its WM_HINTS property. The WM_STATE icon may be a window that the window manager has supplied and that contains the client's icon pixmap, or it may be an ancestor of the client's icon window.

4.1.3.2. WM_ICON_SIZE Property

For more details see section 14.1.12 in Xlib - C Language X Interface.

4.1.4. Changing Window State

• NormalState - The client's top-level window is viewable.
• IconicState - The client's top-level window is iconic (whatever that means for this window manager). The client can assume that its top-level window is not viewable, its icon_window (if any) will be viewable and, failing that, its icon_pixmap (if any) or its WM_ICON_NAME will be displayed.
• WithdrawnState - Neither the client's top-level window nor its icon is visible.

Newly created top-level windows are in the Withdrawn state. Once the window has been provided with suitable properties, the client is free to change its state as follows:

• Withdrawn -> Normal - The client should map the window with WM_HINTS.initial_state being NormalState .
• Withdrawn -> Iconic - The client should map the window with WM_HINTS.initial_state being IconicState .
• Normal -> Iconic - The client should send a ClientMessage event as described later in this section.
• Normal -> Withdrawn - The client should unmap the window and follow it with a synthetic UnmapNotify event as described later in this section.
• Iconic -> Normal - The client should map the window. The contents of WM_HINTS.initial_state are irrelevant in this case.
• Iconic -> Withdrawn - The client should unmap the window and follow it with a synthetic UnmapNotify event as described later in this section.

Advice to Implementors

Clients can select for StructureNotify on their top-level windows to track transitions between Normal and Iconic states. Receipt of a MapNotify event will indicate a transition to the Normal state, and receipt of an UnmapNotify event will indicate a transition to the Iconic state.

When changing the state of the window to Withdrawn, the client must (in addition to unmapping the window) send a synthetic UnmapNotify event by using a SendEvent request with the following arguments:

Argument	Value
destination:	The root
propagate:	False
event-mask:	( SubstructureRedirect|SubstructureNotify )
event: an UnmapNotify with:
event:	The root
window:	The window itself
from-configure:	False

Rationale

The reason for requiring the client to send a synthetic UnmapNotify event is to ensure that the window manager gets some notification of the client's desire to change state, even though the window may already be unmapped when the desire is expressed.

Advice to Implementors

For compatibility with obsolete clients, window managers should trigger the transition to the Withdrawn state on the real UnmapNotify rather than waiting for the synthetic one. They should also trigger the transition if they receive a synthetic UnmapNotify on a window for which they have not yet received a real UnmapNotify .

When a client withdraws a window, the window manager will then update or remove the WM_STATE property as described in section 4.1.3.1. Clients that want to re-use a client window (e.g. by mapping it again or reparenting it elsewhere) after withdrawing it must wait for the withdrawal to be complete before proceeding. The preferred method for doing this is for clients to wait for the window manager to update or remove the WM_STATE property.¹²

If the transition is from the Normal to the Iconic state, the client should send a ClientMessage event to the root with:

• Window == the window to be iconified
• Type¹³ == the atom WM_CHANGE_STATE
• Format == 32
• Data[0] == IconicState

Rationale

The format of this ClientMessage event does not match the format of ClientMessages in section 4.2.8. This is because they are sent by the window manager to clients, and this message is sent by clients to the window manager.

Other values of data[0] are reserved for future extensions to these conventions. The parameters of the SendEvent request should be those described for the synthetic UnmapNotify event.

Advice to Implementors

Clients can also select for VisibilityChange events on their top-level or icon windows. They will then receive a VisibilityNotify (state==FullyObscured) event when the window concerned becomes completely obscured even though mapped (and thus, perhaps a waste of time to update) and a VisibilityNotify (state!=FullyObscured) event when it becomes even partly viewable.

Advice to Implementors

When a window makes a transition from the Normal state to either the Iconic or to the Withdrawn state, clients should be aware that the window manager may make transients for this window inaccessible. Clients should not rely on transient windows being available to the user when the transient owner window is not in the Normal state. When withdrawing a window, clients are advised to withdraw transients for the window.

4.1.5. Configuring the Window

• The [x,y] location of the window's upper left-outer corner
• The [width,height] of the inner region of the window (excluding borders)
• The border width of the window
• The window's position in the stack

• Not changing the size, location, border width, or stacking order of the window at all.

  A client will receive a synthetic ConfigureNotify event that describes the (unchanged) geometry of the window. The (x,y) coordinates will be in the root coordinate system, adjusted for the border width the client requested, irrespective of any reparenting that has taken place. The border_width will be the border width the client requested. The client will not receive a real ConfigureNotify event because no change has actually taken place.

• Moving or restacking the window without resizing it or changing its border width.

  A client will receive a synthetic ConfigureNotify event following the change that describes the new geometry of the window. The event's (x,y) coordinates will be in the root coordinate system adjusted for the border width the client requested. The border_width will be the border width the client requested. The client may not receive a real ConfigureNotify event that describes this change because the window manager may have reparented the top-level window. If the client does receive a real event, the synthetic event will follow the real one.

• Resizing the window or changing its border width (regardless of whether the window was also moved or restacked).

  A client that has selected for StructureNotify events will receive a real ConfigureNotify event. Note that the coordinates in this event are relative to the parent, which may not be the root if the window has been reparented. The coordinates will reflect the actual border width of the window (which the window manager may have changed). The TranslateCoordinates request can be used to convert the coordinates if required.

Advice to Implementors

Clients cannot distinguish between the case where a top-level window is resized and moved from the case where the window is resized but not moved, since a real ConfigureNotify event will be received in both cases. Clients that are concerned with keeping track of the absolute position of a top-level window should keep a piece of state indicating whether they are certain of its position. Upon receipt of a real ConfigureNotify event on the top-level window, the client should note that the position is unknown. Upon receipt of a synthetic ConfigureNotify event, the client should note the position as known, using the position in this event. If the client receives a KeyPress , KeyRelease , ButtonPress , ButtonRelease , MotionNotify , EnterNotify , or LeaveNotify event on the window (or on any descendant), the client can deduce the top-level window's position from the difference between the (event-x, event-y) and (root-x, root-y) coordinates in these events. Only when the position is unknown does the client need to use the TranslateCoordinates request to find the position of a top-level window.

Clients should be aware that their borders may not be visible. Window managers are free to use reparenting techniques to decorate client's top-level windows with borders containing titles, controls, and other details to maintain a consistent look-and-feel. If they do, they are likely to override the client's attempts to set the border width and set it to zero. Clients, therefore, should not depend on the top-level window's border being visible or use it to display any critical information. Other window managers will allow the top-level windows border to be visible.

Convention

Clients should set the desired value of the border-width attribute on all ConfigureWindow requests to avoid a race condition.

Clients that change their position in the stack must be aware that they may have been reparented, which means that windows that used to be siblings no longer are. Using a nonsibling as the sibling parameter on a ConfigureWindow request will cause an error.

Convention

Clients that use a ConfigureWindow request to request a change in their position in the stack should do so using None in the sibling field.

Clients that must position themselves in the stack relative to some window that was originally a sibling must do the ConfigureWindow request (in case they are running under a nonreparenting window manager), be prepared to deal with a resulting error, and then follow with a synthetic ConfigureRequest event by invoking a SendEvent request with the following arguments:

Argument	Value
destination:	The root
propagate:	False
event-mask:	( SubstructureRedirect|SubstructureNotify )
event: a ConfigureRequest with:
event:	The root
window:	The window itself
...	Other parameters from the ConfigureWindow request

Window managers are in any case free to position windows in the stack as they see fit, and so clients should not rely on receiving the stacking order they have requested. Clients should ignore the above-sibling field of both real and synthetic ConfigureNotify events received on their top-level windows because this field may not contain useful information.

4.1.6. Changing Window Attributes

Most attributes are private to the client and will never be interfered with by the window manager. For the attributes that are not private to the client:

• The window manager is free to override the window gravity; a reparenting window manager may want to set the top-level window's window gravity for its own purposes.
• Clients are free to set the save-under hint on their top-level windows, but they must be aware that the hint may be overridden by the window manager.
• Windows, in effect, have per-client event masks, and so, clients may select for whatever events are convenient irrespective of any events the window manager is selecting for. There are some events for which only one client at a time may select, but the window manager should not select for them on any of the client's windows.
• Clients can set override-redirect on top-level windows but are encouraged not to do so except as described in sections 4.1.10 and 4.2.9.

4.1.7. Input Focus

• No Input - The client never expects keyboard input. An example would be xload or another output-only client.
• Passive Input - The client expects keyboard input but never explicitly sets the input focus. An example would be a simple client with no subwindows, which will accept input in PointerRoot mode or when the window manager sets the input focus to its top-level window (in click-to-type mode).
• Locally Active Input - The client expects keyboard input and explicitly sets the input focus, but it only does so when one of its windows already has the focus. An example would be a client with subwindows defining various data entry fields that uses Next and Prev keys to move the input focus between the fields. It does so when its top-level window has acquired the focus in PointerRoot mode or when the window manager sets the input focus to its top-level window (in click-to-type mode).
• Globally Active Input - The client expects keyboard input and explicitly sets the input focus, even when it is in windows the client does not own. An example would be a client with a scroll bar that wants to allow users to scroll the window without disturbing the input focus even if it is in some other window. It wants to acquire the input focus when the user clicks in the scrolled region but not when the user clicks in the scroll bar itself. Thus, it wants to prevent the window manager from setting the input focus to any of its windows.

Passive and Locally Active clients set the input field of WM_HINTS to True , which indicates that they require window manager assistance in acquiring the input focus. No Input and Globally Active clients set the input field to False , which requests that the window manager not set the input focus to their top-level window.

Clients that use a SetInputFocus request must set the time field to the timestamp of the event that caused them to make the attempt. This cannot be a FocusIn event because they do not have timestamps. Clients may also acquire the focus without a corresponding EnterNotify . Note that clients must not use CurrentTime in the time field.

Clients using the Globally Active model can only use a SetInputFocus request to acquire the input focus when they do not already have it on receipt of one of the following events:

• ButtonPress
• ButtonRelease
• Passive-grabbed KeyPress
• Passive-grabbed KeyRelease

The method by which the user commands the window manager to set the focus to a window is up to the window manager. For example, clients cannot determine whether they will see the click that transfers the focus.

Windows with the atom WM_TAKE_FOCUS in their WM_PROTOCOLS property may receive a ClientMessage event from the window manager (as described in section 4.2.8) with WM_TAKE_FOCUS in its data[0] field and a valid timestamp (i.e. not CurrentTime ) in its data[1] field. If they want the focus, they should respond with a SetInputFocus request with its window field set to the window of theirs that last had the input focus or to their default input window, and the time field set to the timestamp in the message. For further information, see section 4.2.7.

A client could receive WM_TAKE_FOCUS when opening from an icon or when the user has clicked outside the top-level window in an area that indicates to the window manager that it should assign the focus (for example, clicking in the headline bar can be used to assign the focus).

The goal is to support window managers that want to assign the input focus to a top-level window in such a way that the top-level window either can assign it to one of its subwindows or can decline the offer of the focus. For example, a clock or a text editor with no currently open frames might not want to take focus even though the window manager generally believes that clients should take the input focus after being deiconified or raised.

Clients that set the input focus need to decide a value for the revert-to field of the SetInputFocus request. This determines the behavior of the input focus if the window the focus has been set to becomes not viewable. The value can be any of the following:

• Parent - In general, clients should use this value when assigning focus to one of their subwindows. Unmapping the subwindow will cause focus to revert to the parent, which is probably what you want.
• PointerRoot - Using this value with a click-to-type focus management policy leads to race conditions because the window becoming unviewable may coincide with the window manager deciding to move the focus elsewhere.
• None - Using this value causes problems if the window manager reparents the window, as most window managers will, and then crashes. The input focus will be None , and there will probably be no way to change it.

Convention

Clients that invoke a SetInputFocus request should set the revert-to argument to Parent .

A convention is also required for clients that want to give up the input focus. There is no safe value set for them to set the input focus to; therefore, they should ignore input material.

Convention

Clients should not give up the input focus of their own volition. They should ignore input that they receive instead.

4.1.8. Colormaps

Clients provide the window manager with hints as to which colormaps to install and uninstall. Clients must not install or uninstall colormaps themselves (except under the circumstances noted below). When a client's top-level window gets the colormap focus (as a result of whatever colormap focus policy is implemented by the window manager), the window manager will ensure that one or more of the client's colormaps are installed.

Clients whose top-level windows and subwindows all use the same colormap should set its ID in the colormap field of the top-level window's attributes. They should not set a WM_COLORMAP_WINDOWS property on the top-level window. If they want to change the colormap, they should change the top-level window's colormap attribute. The window manager will track changes to the window's colormap attribute and install colormaps as appropriate.

Clients that create windows can use the value CopyFromParent to inherit their parent's colormap. Window managers will ensure that the root window's colormap field contains a colormap that is suitable for clients to inherit. In particular, the colormap will provide distinguishable colors for BlackPixel and WhitePixel .

Top-level windows that have subwindows or override-redirect pop-up windows whose colormap requirements differ from the top-level window should have a WM_COLORMAP_WINDOWS property. This property contains a list of IDs for windows whose colormaps the window manager should attempt to have installed when, in the course of its individual colormap focus policy, it assigns the colormap focus to the top-level window (see section 4.1.2.8). The list is ordered by the importance to the client of having the colormaps installed. The window manager will track changes to this property and will track changes to the colormap attribute of the windows in the property.

If the relative importance of colormaps changes, the client should update the WM_COLORMAP_WINDOWS property to reflect the new ordering. If the top-level window does not appear in the list, the window manager will assume it to be of higher priority than any window in the list.

WM_TRANSIENT_FOR windows either can have their own WM_COLORMAP_WINDOWS property or can appear in the property of the window they are transient for, as appropriate.

Rationale

An alternative design was considered for how clients should hint to the window manager about their colormap requirements. This alternative design specified a list of colormaps instead of a list of windows. The current design, a list of windows, was chosen for two reasons. First, it allows window managers to find the visuals of the colormaps, thus permitting visual-dependent colormap installation policies. Second, it allows window managers to select for VisibilityChange events on the windows concerned and to ensure that colormaps are only installed if the windows that need them are visible. The alternative design allows for neither of these policies.

Advice to Implementors

Clients should be aware of the min-installed-maps and max-installed-maps fields of the connection setup information, and the effect that the minimum value has on the "required list" defined by the Protocol in the description of the InstallColormap request. Briefly, the min-installed-maps most recently installed maps are guaranteed to be installed. This value is often one; clients needing multiple colormaps should beware.

Whenever possible, clients should use the mechanisms described above and let the window manager handle colormap installation. However, clients are permitted to perform colormap installation on their own while they have the pointer grabbed. A client performing colormap installation must notify the window manager prior to the first installation. When the client has finished its colormap installation, it must also notify the window manager. The client notifies the window manager by issuing a SendEvent request with the following arguments:

Argument	Value
destination:	the root window of the screen on which the colormap is being installed
propagate:	False
event-mask:	ColormapChange
event: a ClientMessage with:
window:	the root window, as above
type:	WM_COLORMAP_NOTIFY
format:	32
data[0]:	the timestamp of the event that caused the client to start or stop installing colormaps
data[1]:	1 if the client is starting colormap installation, 0 if the client is finished with colormap installation
data[2]:	reserved, must be zero
data[3]:	reserved, must be zero
data[4]:	reserved, must be zero

This feature was introduced in version 2.0 of this document, and there will be a significant period of time before all window managers can be expected to implement this feature. Before using this feature, clients must check the compliance level of the window manager (using the mechanism described in section 4.3) to verify that it supports this feature. This is necessary to prevent colormap installation conflicts between clients and older window managers.

Window managers should refrain from installing colormaps while a client has requested control of colormap installation. The window manager should continue to track the set of installed colormaps so that it can reinstate its colormap focus policy when the client has finished colormap installation.

This technique has race conditions that may result in the colormaps continuing to be installed even after a client has issued its notification message. For example, the window manager may have issued some InstallColormap requests that are not executed until after the client's SendEvent and InstallColormap requests, thus uninstalling the client's colormaps. If this occurs while the client still has the pointer grabbed and before the client has issued the "finished" message, the client may reinstall the desired colormaps.

Advice to Implementors

Clients are expected to use this mechanism for things such as popup windows and for animations that use override-redirect windows. If a client fails to issue the "finished" message, the window manager may be left in a state where its colormap installation policy is suspended. Window manager implementors may want to implement a feature that resets colormap installation policy in response to a command from the user.

4.1.9. Icons

• A string in WM_ICON_NAME

  All clients should do this because it provides a fallback for window managers whose ideas about icons differ widely from those of the client.

• A Pixmap into the icon_pixmap field of the WM_HINTS property and possibly another into the icon_mask field

  The window manager is expected to display the pixmap masked by the mask. The pixmap should be one of the sizes found in the WM_ICON_SIZE property on the root. If this property is not found, the window manager is unlikely to display icon pixmaps. Window managers usually will clip or tile pixmaps that do not match WM_ICON_SIZE.

• A window into the icon_window field of the WM_HINTS property

  The window manager is expected to map that window whenever the client is in the Iconic state. In general, the size of the icon window should be one of those specified in WM_ICON_SIZE on the root, if it exists. Window managers are free to resize icon windows.

• If the window's WM_HINTS.icon_window is set, the window it names is visible.
• If the window's WM_HINTS.icon_window is not set but the window's WM_HINTS.icon_pixmap is set, the pixmap it names is visible.
• Otherwise, the window's WM_ICON_NAME string is visible.

Conventions

1. The icon window should be an InputOutput child of the root.
2. The icon window should be one of the sizes specified in the WM_ICON_SIZE property on the root.
3. The icon window should use the root visual and default colormap for the screen in question.
4. Clients should not map their icon windows.
5. Clients should not unmap their icon windows.
6. Clients should not configure their icon windows.
7. Clients should not set override-redirect on their icon windows or select for ResizeRedirect events on them.
8. Clients must not depend on being able to receive input events by means of their icon windows.
9. Clients must not manipulate the borders of their icon windows.
10. Clients must select for Exposure events on their icon window and repaint it when requested.

Window managers will differ as to whether they support input events to client's icon windows; most will allow the client to receive some subset of the keys and buttons.

Window managers will ignore any WM_NAME, WM_ICON_NAME, WM_NORMAL_HINTS, WM_HINTS, WM_CLASS, WM_TRANSIENT_FOR, WM_PROTOCOLS, WM_COLORMAP_WINDOWS, WM_COMMAND, or WM_CLIENT_MACHINE properties they find on icon windows.

4.1.10. Pop-up Windows

They can create and map another normal top-level window, which will get decorated and managed as normal by the window manager. See the discussion of window groups that follows.
1. If the window will be visible for a relatively short time and deserves a somewhat lighter treatment, they can set the WM_TRANSIENT_FOR property. They can expect less decoration but can set all the normal window manager properties on the window. An example would be a dialog box.
2. If the window will be visible for a very short time and should not be decorated at all, the client can set override-redirect on the window. In general, this should be done only if the pointer is grabbed while the window is mapped. The window manager will never interfere with these windows, which should be used with caution. An example of an appropriate use is a pop-up menu.

Advice to Implementors

The user will not be able to move, resize, restack, or transfer the input focus to override-redirect windows, since the window manager is not managing them. If it is necessary for a client to receive keystrokes on an override-redirect window, either the client must grab the keyboard, or the client must have another top-level window that is not override-redirect and that has selected the Locally Active or Globally Active focus model. The client may set the focus to the override-redirect window when the other window receives a WM_TAKE_FOCUS message or one of the events listed in section 4.1.7 in the description of the Globally Active focus model.

Window managers are free to decide if WM_TRANSIENT_FOR windows should be iconified when the window they are transient for is. Clients displaying WM_TRANSIENT_FOR windows that have (or request to have) the window they are transient for iconified do not need to request that the same operation be performed on the WM_TRANSIENT_FOR window; the window manager will change its state if that is the policy it wishes to enforce.

4.1.11. Window Groups

One of the windows (that is, the one the others point to) will be the group leader and will carry the group as opposed to the individual properties. Window managers may treat the group leader differently from other windows in the group. For example, group leaders may have the full set of decorations, and other group members may have a restricted set.

It is not necessary that the client ever map the group leader; it may be a window that exists solely as a placeholder.

It is up to the window manager to determine the policy for treating the windows in a group. At present, there is no way for a client to request a group, as opposed to an individual, operation.

4.2. Client Responses to Window Manager Actions

4.2.1. Reparenting

• The parent value returned by a QueryTree request will no longer be the value supplied to the CreateWindow request that created the reparented window. There should be no need for the client to be aware of the identity of the window to which the top-level window has been reparented. In particular, a client that wishes to create further top-level windows should continue to use the root as the parent for these new windows.
• The server will interpret the (x,y) coordinates in a ConfigureWindow request in the new parent's coordinate space. In fact, they usually will not be interpreted by the server because a reparenting window manager usually will have intercepted these operations (see section 4.2.2). Clients should use the root coordinate space for these requests (see section 4.1.5).
• ConfigureWindow requests that name a specific sibling window may fail because the window named, which used to be a sibling, no longer is after the reparenting operation (see section 4.1.5).
• The (x,y) coordinates returned by a GetGeometry request are in the parent's coordinate space and are thus not directly useful after a reparent operation.
• A background of ParentRelative will have unpredictable results.
• A cursor of None will have unpredictable results.

If the window manager reparents a client's window, the reparented window will be placed in the save-set of the parent window. This means that the reparented window will not be destroyed if the window manager terminates and will be remapped if it was unmapped. Note that this applies to all client windows the window manager reparents, including transient windows and client icon windows.

4.2.2. Redirection of Operations

The possibility that a request may be redirected means that a client cannot assume that any redirectable request is actually performed when the request is issued or is actually performed at all. The requests that may be redirected are MapWindow , ConfigureWindow , and CirculateWindow .

Advice to Implementors

The following is incorrect because the MapWindow request may be intercepted and the PolyLine output made to an unmapped window:

MapWindow A
PolyLine A GC   ...

The client must wait for an Expose event before drawing in the window.¹⁴

This next example incorrectly assumes that the ConfigureWindow request is actually executed with the arguments supplied:

ConfigureWindow width=N height=M

The client should select for StructureNotify on its window and monitor the window's size by tracking ConfigureNotify events.

Clients must be especially careful when attempting to set the focus to a window that they have just mapped. This sequence may result in an X protocol error:

MapWindow B
SetInputFocus B

If the MapWindow request has been intercepted, the window will still be unmapped, causing the SetInputFocus request to generate the error. The solution to this problem is for clients to select for VisibilityChange on the window and to delay the issuance of the SetInputFocus request until they have received a VisibilityNotify event indicating that the window is visible.

This technique does not guarantee correct operation. The user may have iconified the window by the time the SetInputFocus request reaches the server, still causing an error. Or, the window manager may decide to map the window into Iconic state, in which case the window will not be visible. This will delay the generation of the VisibilityNotify event indefinitely. Clients must be prepared to handle these cases.

A window with the override-redirect bit set is immune from redirection, but the bit should be set on top-level windows only in cases where other windows should be prevented from processing input while the override-redirect window is mapped (see section 4.1.10) and while responding to ResizeRequest events (see section 4.2.9).

Clients that have no non-Withdrawn top-level windows and that map an override-redirect top-level window are taking over total responsibility for the state of the system. It is their responsibility to:

• Prevent any preexisting window manager from interfering with their activities
• Restore the status quo exactly after they unmap the window so that any preexisting window manager does not get confused

4.2.3. Window Move

Any real ConfigureNotify event on a top-level window implies that the window's position on the root may have changed, even though the event reports that the window's position in its parent is unchanged because the window may have been reparented. Note that the coordinates in the event will not, in this case, be directly useful.

The window manager will send these events by using a SendEvent request with the following arguments:

Argument	Value
destination:	The client's window
propagate:	False
event-mask:	StructureNotify

4.2.4. Window Resize

The response of the client to being resized should be to accept the size it has been given and to do its best with it. Clients must not respond to being resized by attempting to resize themselves to a better size. If the size is impossible to work with, clients are free to request to change to the Iconic state.

4.2.5. Iconify and Deiconify

The client can elect to be notified of these state changes by selecting for StructureNotify events on the top-level window. It will receive a UnmapNotify event when it goes Iconic and a MapNotify event when it goes Normal.

4.2.6. Colormap Change

4.2.7. Input Focus

• Set the input field of WM_HINTS to True and actually have the input focus in one of their top-level windows
• Set the input field of WM_HINTS to False and have received a suitable event as described in section 4.1.7
• Have received a WM_TAKE_FOCUS message as described in section 4.1.7

Once a client satisfies these conditions, it may transfer the focus to another of its windows by using the SetInputFocus request, which is defined as follows:

SetInputFocus

focus :	WINDOW or PointerRoot or None
revert-to :	{ Parent , PointerRoot , None }
time :	TIMESTAMP or CurrentTime

Conventions

1. Clients that use a SetInputFocus request must set the time argument to the timestamp of the event that caused them to make the attempt. This cannot be a FocusIn event because they do not have timestamps. Clients may also acquire the focus without a corresponding EnterNotify event. Clients must not use CurrentTime for the time argument.
2. Clients that use a SetInputFocus request to set the focus to one of their windows must set the revert-to field to Parent .

4.2.8. ClientMessage Events

Top-level windows with a WM_PROTOCOLS property may be sent ClientMessage events specific to the protocols named by the atoms in the property (see section 4.1.2.7). For all protocols, the ClientMessage events have the following:

• WM_PROTOCOLS as the type field
• Format 32
• The atom that names their protocol in the data[0] field
• A timestamp in their data[1] field

These events will be sent by using a SendEvent request with the following arguments:

Argument	Value
destination:	The client's window
propagate:	False
event-mask:	() empty
event:	As specified by the protocol

4.2.8.1. Window Deletion

Clients receiving a WM_DELETE_WINDOW message should behave as if the user selected "delete window" from a hypothetical menu. They should perform any confirmation dialog with the user and, if they decide to complete the deletion, should do the following:

• Either change the window's state to Withdrawn (as described in section 4.1.4) or destroy the window
• Destroy any internal state associated with the window

Clients are permitted to interact with the user and ask, for example, whether a file associated with the window to be deleted should be saved or the window deletion should be cancelled. Clients are not required to destroy the window itself; the resource may be reused, but all associated state (for example, backing store) should be released.

If the client aborts a destroy and the user then selects DELETE WINDOW again, the window manager should start the WM_DELETE_WINDOW protocol again. Window managers should not use DestroyWindow requests on a window that has WM_DELETE_WINDOW in its WM_PROTOCOLS property.

Clients that choose not to include WM_DELETE_WINDOW in the WM_PROTOCOLS property may be disconnected from the server if the user asks for one of the client's top-level windows to be deleted.

4.2.9. Redirecting Requests

Convention

Clients (including window managers) should select for SubstructureRedirect and ResizeRedirect events only on windows that they own.

In particular, clients that need to take some special action if they are resized can select for ResizeRedirect events on their top-level windows. They will receive a ResizeRequest event if the window manager resizes their window, and the resize will not actually take place. Clients are free to make what use they like of the information that the window manager wants to change their size, but they must configure the window to the width and height specified in the event in a timely fashion. To ensure that the resize will actually happen at this stage instead of being intercepted and executed by the window manager (and thus restarting the process), the client needs temporarily to set override-redirect on the window.

Convention

Clients receiving ResizeRequest events must respond by doing the following:

• Setting override-redirect on the window specified in the event
• Configuring the window specified in the event to the width and height specified in the event as soon as possible and before making any other geometry requests
• Clearing override-redirect on the window specified in the event

4.3. Communication with the Window Manager by Means of Selections

Atom	Type	Data Received
VERSION	INTEGER	Two integers, which are the major and minor release numbers (respectively) of the ICCCM with which the window manager complies. For this version of the ICCCM, the numbers are 2 and 0.15

4.4. Summary of Window Manager Property Types