# Inter-Client Communication Functions

The Inter-Client Communication Conventions Manual, hereafter referred to as the ICCCM, details the X Consortium approved conventions that govern inter-client communications. These conventions ensure peer-to-peer client cooperation in the use of selections, cut buffers, and shared resources as well as client cooperation with window and session managers. For further information, see the Inter-Client Communication Conventions Manual.

Xlib provides a number of standard properties and programming interfaces that are ICCCM compliant. The predefined atoms for some of these properties are defined in the <X11/Xatom.h> header file, where to avoid name conflicts with user symbols their #define name has an XA_ prefix. For further information about atoms and properties, see section 4.3.

Xlib’s selection and cut buffer mechanisms provide the primary programming interfaces by which peer client applications communicate with each other (see sections 4.5 and 16.6). The functions discussed in this chapter provide the primary programming interfaces by which client applications communicate with their window and session managers as well as share standard colormaps.

The standard properties that are of special interest for communicating with window and session managers are:

Name | Type | Format | Description
--- | --- | --- | ---
WM_CLASS | STRING | 8 | Set by application programs to allow window and session managers to obtain the application’s resources from the resource database.
WM_CLIENT_MACHINE | TEXT |  | The string name of the machine on which the client application is running.
WM_COLORMAP_WINDOWS | WINDOWS | 32 | The list of window IDs that may need a different colormap from that of their top-level window.
WM_COMMAND | TEXT |  | The command and arguments, null separated, used to invoke the application.
WM_HINTS | WM_HINTS | 32 | Additional hints set by the client for use by the window manager. The C type of this property is XWMHints.
WM_ICON_NAME | TEXT |  | The name to be used in an icon.
WM_ICON_SIZE | WM_ICON_SIZE | 32 | The window manager may set this property on the root window to specify the icon sizes it supports. The C type of this property is XIconSize.
WM_NAME | TEXT |  | The name of the application.
WM_NORMAL_HINTS | WM_NORMAL_HINTS | 32 | Size hints for a window in its normal state. The C type of this property is XSizeHints.
WM_PROTOCOLS | ATOM | 32 | List of atoms that identify the communications protocols between the client and window manager in which the client is willing to participate.
WM_STATE | WM_STATE | 32 | Intended for communication between window and session managers only.
WM_TRANSIENT_FOR | WINDOW | 32 | Set by application programs to indicate to the window manager that a transient top-level window, such as a dialog box.

The remainder of this chapter discusses:

- Client to window manager communication

- Client to session manager communication

- Standard colormaps

## Client to Window Manager Communication

This section discusses how to:

- Manipulate top-level windows

- Convert string lists

- Set and read text properties

- Set and read the WM_NAME property

- Set and read the WM_ICON_NAME property

- Set and read the WM_HINTS property

- Set and read the WM_NORMAL_HINTS property

- Set and read the WM_CLASS property

- Set and read the WM_TRANSIENT_FOR property

- Set and read the WM_PROTOCOLS property

- Set and read the WM_COLORMAP_WINDOWS property

- Set and read the WM_ICON_SIZE property

- Use window manager convenience functions

### Manipulating Top-Level Windows

Xlib provides functions that you can use to change the visibility or size of top-level windows (that is, those that were created as children of the root window). Note that the subwindows that you create are ignored by window managers. Therefore, you should use the basic window functions described in chapter 3 to manipulate your application's subwindows.

To request that a top-level window be iconified, use .

      Status XIconifyWindow
      Display *display
      Window w
      int screen_number

display

  Specifies the connection to the X server.

w

  Specifies the window.

screen_number

  Specifies the appropriate screen number on the host server.

The function sends a WM_CHANGE_STATE ClientMessage event with a format of 32 and a first data element of IconicState (as described in section 4.1.4 of the Inter-Client Communication Conventions Manual) and a window of w to the root window of the specified screen with an event mask set to SubstructureNotifyMask | SubstructureRedirectMask. Window managers may elect to receive this message and if the window is in its normal state, may treat it as a request to change the window's state from normal to iconic. If the WM_CHANGE_STATE property cannot be interned, does not send a message and returns a zero status. It returns a nonzero status if the client message is sent successfully; otherwise, it returns a zero status.

To request that a top-level window be withdrawn, use .

      Status XWithdrawWindow
      Display *display
      Window w
      int screen_number

display

  Specifies the connection to the X server.

w

  Specifies the window.

screen_number

  Specifies the appropriate screen number on the host server.

The function unmaps the specified window and sends a synthetic UnmapNotify event to the root window of the specified screen. Window managers may elect to receive this message and may treat it as a request to change the window's state to withdrawn. When a window is in the withdrawn state, neither its normal nor its iconic representations is visible. It returns a nonzero status if the UnmapNotify event is successfully sent; otherwise, it returns a zero status.

can generate a BadWindow error.

To request that a top-level window be reconfigured, use .

      Status XReconfigureWMWindow
      Display *display
      Window w
      int screen_number
      unsignedint value_mask
      XWindowChanges *values

display

  Specifies the connection to the X server.

w

  Specifies the window.

screen_number

  Specifies the appropriate screen number on the host server.

value_mask

  Specifies which values are to be set using information in the values structure. This mask is the bitwise inclusive OR of the valid configure window values bits.

values

  Specifies the XWindowChanges structure.

The function issues a ConfigureWindow request on the specified top-level window. If the stacking mode is changed and the request fails with a BadMatch error, the error is trapped by Xlib and a synthetic ConfigureRequestEvent containing the same configuration parameters is sent to the root of the specified window. Window managers may elect to receive this event and treat it as a request to reconfigure the indicated window. It returns a nonzero status if the request or event is successfully sent; otherwise, it returns a zero status.

can generate BadValue and BadWindow errors.

### Converting String Lists

Many of the text properties allow a variety of types and formats. Because the data stored in these properties are not simple null-terminated strings, an XTextProperty structure is used to describe the encoding, type, and length of the text as well as its value. The XTextProperty structure contains:

    typedef struct {
    	unsigned char *value;	/* property data */
    	Atom encoding;	/* type of property */
    	int format;	/* 8, 16, or 32 */
    	unsigned long nitems;	/* number of items in value */
    } XTextProperty;

Xlib provides functions to convert localized text to or from encodings that support the inter-client communication conventions for text. In addition, functions are provided for converting between lists of pointers to character strings and text properties in the STRING encoding.

The functions for localized text return a signed integer error status that encodes Success as zero, specific error conditions as negative numbers, and partial conversion as a count of unconvertible characters.

    #define #XNoMemory           -1
    #define #XLocaleNotSupported -2
    #define #XConverterNotFound  -3

    typedef enum {
    	XStringStyle,		/* STRING */
    	XCompoundTextStyle,	/* COMPOUND_TEXT */
    	XTextStyle,		/* text in owner's encoding (current locale) */
    	XStdICCTextStyle	/* STRING, else COMPOUND_TEXT */
    } XICCEncodingStyle;

To convert a list of text strings to an XTextProperty structure, use or .

      int XmbTextListToTextProperty
      Display *display
      char **list
      int count
      XICCEncodingStyle style
      XTextProperty *text_prop_return

      int XwcTextListToTextProperty
      Display *display
      wchar_t **list
      int count
      XICCEncodingStyle style
      XTextProperty *text_prop_return

display

  Specifies the connection to the X server.

list

  Specifies a list of null-terminated character strings.

count

  Specifies the number of strings specified.

style

  Specifies the manner in which the property is encoded.

text_prop_return

  Returns the XTextProperty structure.

The and functions set the specified XTextProperty value to a set of null-separated elements representing the concatenation of the specified list of null-terminated text strings. A final terminating null is stored at the end of the value field of text_prop_return but is not included in the nitems member.

The functions set the encoding field of text_prop_return to an Atom for the specified display naming the encoding determined by the specified style and convert the specified text list to this encoding for storage in the text_prop_return value field. If the style `XStringStyle` or `XCompoundTextStyle` is specified, this encoding is ``STRING'' or ``COMPOUND_TEXT'', respectively. If the style `XTextStyle` is specified, this encoding is the encoding of the current locale. If the style `XStdICCTextStyle` is specified, this encoding is ``STRING'' if the text is fully convertible to STRING, else ``COMPOUND_TEXT''.

If insufficient memory is available for the new value string, the functions return XNoMemory. If the current locale is not supported, the functions return XLocaleNotSupported. In both of these error cases, the functions do not set text_prop_return.

To determine if the functions are guaranteed not to return XLocaleNotSupported, use `XSupportsLocale`.

If the supplied text is not fully convertible to the specified encoding, the functions return the number of unconvertible characters. Each unconvertible character is converted to an implementation-defined and encoding-specific default string. Otherwise, the functions return Success. Note that full convertibility to all styles except `XStringStyle` is guaranteed.

To free the storage for the value field, use .

To obtain a list of text strings from an XTextProperty structure, use or .

      int XmbTextPropertyToTextList
      Display *display
      XTextProperty *text_prop
      char ***list_return
      int *count_return

      int XwcTextPropertyToTextList
      Display *display
      XTextProperty *text_prop
      wchar_t ***list_return
      int *count_return

display

  Specifies the connection to the X server.

text_prop

  Specifies the XTextProperty structure to be used.

list_return

  Returns a list of null-terminated character strings.

count_return

  Returns the number of (Cn.

The and functions return a list of text strings in the current locale representing the null-separated elements of the specified XTextProperty structure. The data in text_prop must be format 8.

Multiple elements of the property (for example, the strings in a disjoint text selection) are separated by a null byte. The contents of the property are not required to be null-terminated; any terminating null should not be included in text_prop.nitems.

If insufficient memory is available for the list and its elements, and return XNoMemory. If the current locale is not supported, the functions return XLocaleNotSupported. Otherwise, if the encoding field of text_prop is not convertible to the encoding of the current locale, the functions return XConverterNotFound. For supported locales, existence of a converter from COMPOUND_TEXT, STRING or the encoding of the current locale is guaranteed if `XSupportsLocale` returns True for the current locale (but the actual text may contain unconvertible characters). Conversion of other encodings is implementation-dependent. In all of these error cases, the functions do not set any return values.

Otherwise, and return the list of null-terminated text strings to list_return and the number of text strings to count_return.

If the value field of text_prop is not fully convertible to the encoding of the current locale, the functions return the number of unconvertible characters. Each unconvertible character is converted to a string in the current locale that is specific to the current locale. To obtain the value of this string, use `XDefaultString`. Otherwise, and return Success.

To free the storage for the list and its contents returned by , use . To free the storage for the list and its contents returned by , use .

To free the in-memory data associated with the specified wide character string list, use .

      void XwcFreeStringList
      wchar_t **list

list

  Specifies the list of strings to be freed.

The function frees memory allocated by .

To obtain the default string for text conversion in the current locale, use

char *XDefaultString()

The `XDefaultString` function returns the default string used by Xlib for text conversion (for example, in ). The default string is the string in the current locale that is output when an unconvertible character is found during text conversion. If the string returned by `XDefaultString` is the empty string (""), no character is output in the converted text. `XDefaultString` does not return NULL.

The string returned by `XDefaultString` is independent of the default string for text drawing; see to obtain the default string for an XFontSet.

The behavior when an invalid codepoint is supplied to any Xlib function is undefined.

The returned string is null-terminated. It is owned by Xlib and should not be modified or freed by the client. It may be freed after the current locale is changed. Until freed, it will not be modified by Xlib.

To set the specified list of strings in the STRING encoding to a XTextProperty structure, use .

      Status XStringListToTextProperty
      char **list
      int count
      XTextProperty *text_prop_return

list

  Specifies a list of null-terminated character strings.

count

  Specifies the number of (Cn.

text_prop_return

  Returns the XTextProperty structure.

The function sets the specified XTextProperty to be of type STRING (format 8) with a value representing the concatenation of the specified list of null-separated character strings. An extra null byte (which is not included in the nitems member) is stored at the end of the value field of text_prop_return. The strings are assumed (without verification) to be in the STRING encoding. If insufficient memory is available for the new value string, does not set any fields in the XTextProperty structure and returns a zero status. Otherwise, it returns a nonzero status. To free the storage for the value field, use .

To obtain a list of strings from a specified XTextProperty structure in the STRING encoding, use .

      Status XTextPropertyToStringList
      XTextProperty *text_prop
      char ***list_return
      int *count_return

text_prop

  Specifies the XTextProperty structure to be used.

list_return

  Returns a list of null-terminated character strings.

count_return

  Returns the number of (Cn.

The function returns a list of strings representing the null-separated elements of the specified XTextProperty structure. The data in text_prop must be of type STRING and format 8. Multiple elements of the property (for example, the strings in a disjoint text selection) are separated by NULL (encoding 0). The contents of the property are not null-terminated. If insufficient memory is available for the list and its elements, sets no return values and returns a zero status. Otherwise, it returns a nonzero status. To free the storage for the list and its contents, use .

To free the in-memory data associated with the specified string list, use .

      void XFreeStringList
      char **list

list

  Specifies the list of strings to be freed.

The function releases memory allocated by and and the missing charset list allocated by .

### Setting and Reading Text Properties

Xlib provides two functions that you can use to set and read the text properties for a given window. You can use these functions to set and read those properties of type TEXT (WM_NAME, WM_ICON_NAME, WM_COMMAND, and WM_CLIENT_MACHINE). In addition, Xlib provides separate convenience functions that you can use to set each of these properties. For further information about these convenience functions, see sections 14.1.4, 14.1.5, 14.2.1, and 14.2.2, respectively.

To set one of a window's text properties, use .

      void XSetTextProperty
      Display *display
      Window w
      XTextProperty *text_prop
      Atom property

display

  Specifies the connection to the X server.

w

  Specifies the window.

text_prop

  Specifies the XTextProperty structure to be used.

property

  Specifies the property name.

The function replaces the existing specified property for the named window with the data, type, format, and number of items determined by the value field, the encoding field, the format field, and the nitems field, respectively, of the specified XTextProperty structure. If the property does not already exist, sets it for the specified window.

can generate BadAlloc, BadAtom, BadValue, and BadWindow errors.

To read one of a window's text properties, use .

      Status XGetTextProperty
      Display *display
      Window w
      XTextProperty *text_prop_return
      Atom property

display

  Specifies the connection to the X server.

w

  Specifies the window.

text_prop_return

  Returns the XTextProperty structure.

property

  Specifies the property name.

The function reads the specified property from the window and stores the data in the returned XTextProperty structure. It stores the data in the value field, the type of the data in the encoding field, the format of the data in the format field, and the number of items of data in the nitems field. An extra byte containing null (which is not included in the nitems member) is stored at the end of the value field of text_prop_return. The particular interpretation of the property's encoding and data as text is left to the calling application. If the specified property does not exist on the window, sets the value field to NULL, the encoding field to None, the format field to zero, and the nitems field to zero.

If it was able to read and store the data in the XTextProperty structure, returns a nonzero status; otherwise, it returns a zero status.

can generate BadAtom and BadWindow errors.

### Setting and Reading the WM_NAME Property

Xlib provides convenience functions that you can use to set and read the WM_NAME property for a given window.

To set a window's WM_NAME property with the supplied convenience function, use .

      void XSetWMName
      Display *display
      Window w
      XTextProperty *text_prop

display

  Specifies the connection to the X server.

w

  Specifies the window.

text_prop

  Specifies the XTextProperty structure to be used.

The convenience function calls to set the WM_NAME property.

To read a window's WM_NAME property with the supplied convenience function, use .

      Status XGetWMName
      Display *display
      Window w
      XTextProperty *text_prop_return

display

  Specifies the connection to the X server.

w

  Specifies the window.

text_prop_return

  Returns the XTextProperty structure.

The convenience function calls to obtain the WM_NAME property. It returns a nonzero status on success; otherwise, it returns a zero status.

The following two functions have been superseded by and , respectively. You can use these additional convenience functions for window names that are encoded as STRING properties.

To assign a name to a window, use .

      XStoreName
      Display *display
      Window w
      char *window_name

display

  Specifies the connection to the X server.

w

  Specifies the window.

window_name

  Specifies the window name, which should be a null-terminated string.

The function assigns the name passed to window_name to the specified window. A window manager can display the window name in some prominent place, such as the title bar, to allow users to identify windows easily. Some window managers may display a window's name in the window's icon, although they are encouraged to use the window's icon name if one is provided by the application. If the string is not in the Host Portable Character Encoding, the result is implementation-dependent.

can generate BadAlloc and BadWindow errors.

To get the name of a window, use .

      Status XFetchName
      Display *display
      Window w
      char **window_name_return

display

  Specifies the connection to the X server.

w

  Specifies the window.

window_name_return

  Returns the window name, which is a null-terminated string.

The function returns the name of the specified window. If it succeeds, it returns a nonzero status; otherwise, no name has been set for the window, and it returns zero. If the WM_NAME property has not been set for this window, sets window_name_return to NULL. If the data returned by the server is in the Latin Portable Character Encoding, then the returned string is in the Host Portable Character Encoding. Otherwise, the result is implementation-dependent. When finished with it, a client must free the window name string using .

can generate a BadWindow error.

### Setting and Reading the WM_ICON_NAME Property

Xlib provides convenience functions that you can use to set and read the WM_ICON_NAME property for a given window.

To set a window's WM_ICON_NAME property, use .

      void XSetWMIconName
      Display *display
      Window w
      XTextProperty *text_prop

display

  Specifies the connection to the X server.

w

  Specifies the window.

text_prop

  Specifies the XTextProperty structure to be used.

The convenience function calls to set the WM_ICON_NAME property.

To read a window's WM_ICON_NAME property, use .

      Status XGetWMIconName
      Display *display
      Window w
      XTextProperty *text_prop_return

display

  Specifies the connection to the X server.

w

  Specifies the window.

text_prop_return

  Returns the XTextProperty structure.

The convenience function calls to obtain the WM_ICON_NAME property. It returns a nonzero status on success; otherwise, it returns a zero status.

The next two functions have been superseded by and , respectively. You can use these additional convenience functions for window names that are encoded as STRING properties.

To set the name to be displayed in a window's icon, use .

      XSetIconName
      Display *display
      Window w
      char *icon_name

display

  Specifies the connection to the X server.

w

  Specifies the window.

icon_name

  Specifies the icon name, which should be a null-terminated string.

If the string is not in the Host Portable Character Encoding, the result is implementation-dependent. can generate BadAlloc and BadWindow errors.

To get the name a window wants displayed in its icon, use .

      Status XGetIconName
      Display *display
      Window w
      char **icon_name_return

display

  Specifies the connection to the X server.

w

  Specifies the window.

icon_name_return

  Returns the window's icon name, which is a null-terminated string.

The function returns the name to be displayed in the specified window's icon. If it succeeds, it returns a nonzero status; otherwise, if no icon name has been set for the window, it returns zero. If you never assigned a name to the window, sets icon_name_return to NULL. If the data returned by the server is in the Latin Portable Character Encoding, then the returned string is in the Host Portable Character Encoding. Otherwise, the result is implementation-dependent. When finished with it, a client must free the icon name string using .

can generate a BadWindow error.

### Setting and Reading the WM_HINTS Property

Xlib provides functions that you can use to set and read the WM_HINTS property for a given window. These functions use the flags and the XWMHints structure, as defined in the `<X11/Xutil.h>`
header file.

To allocate an XWMHints structure, use `XAllocWMHints`.

XWMHints *XAllocWMHints()

The `XAllocWMHints` function allocates and returns a pointer to an XWMHints structure. Note that all fields in the XWMHints structure are initially set to zero. If insufficient memory is available, `XAllocWMHints` returns NULL. To free the memory allocated to this structure, use .

The XWMHints structure contains:

    /* Window manager hints mask bits */

    #define         InputHint             (1L<<0)
    #define         StateHint             (1L<<1)
    #define         IconPixmapHint        (1L<<2)
    #define         IconWindowHint        (1L<<3)
    #define         IconPositionHint      (1L<<4)
    #define         IconMaskHint          (1L<<5)
    #define         WindowGroupHint       (1L<<6)
    #define         UrgencyHint           (1L<<8)
    #define         AllHints              (InputHint|StateHint|IconPixmapHint|
                                           IconWIndowHint|IconPositionHint|
                                           IconMaskHint|WindowGroupHint)

    /* Values */

    typedef struct {
    	long flags;	        /* marks which fields in this structure are defined */
    	Bool input;	        /* does this application rely on the window manager to
    			           get keyboard input? */
    	int initial_state;	/* see below */
    	Pixmap icon_pixmap;	/* pixmap to be used as icon */
    	Window icon_window;	/* window to be used as icon */
    	int icon_x, icon_y;	/* initial position of icon */
    	Pixmap icon_mask;	/* pixmap to be used as mask for icon_pixmap */
    	XID window_group;	/* id of related window group */
    	/* this structure may be extended in the future */
    } XWMHints;

The input member is used to communicate to the window manager the input focus model used by the application. Applications that expect input but never explicitly set focus to any of their subwindows (that is, use the push model of focus management), such as X Version 10 style applications that use real-estate driven focus, should set this member to True. Similarly, applications that set input focus to their subwindows only when it is given to their top-level window by a window manager should also set this member to True. Applications that manage their own input focus by explicitly setting focus to one of their subwindows whenever they want keyboard input (that is, use the pull model of focus management) should set this member to False. Applications that never expect any keyboard input also should set this member to False.

Pull model window managers should make it possible for push model applications to get input by setting input focus to the top-level windows of applications whose input member is True. Push model window managers should make sure that pull model applications do not break them by resetting input focus to PointerRoot when it is appropriate (for example, whenever an application whose input member is False sets input focus to one of its subwindows).

The definitions for the initial_state flag are:

    #define      WithdrawnState 0
    #define      NormalState    1   /* most applications start this way */
    #define      IconicState    2   /* application wants to start as an icon */

The icon_mask specifies which pixels of the icon_pixmap should be used as the icon. This allows for nonrectangular icons. Both icon_pixmap and icon_mask must be bitmaps. The icon_window lets an application provide a window for use as an icon for window managers that support such use. The window_group lets you specify that this window belongs to a group of other windows. For example, if a single application manipulates multiple top-level windows, this allows you to provide enough information that a window manager can iconify all of the windows rather than just the one window.

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 will make some effort to draw the user's attention to this window while this flag is set. The client must provide some means by which the user can cause the urgency flag to be cleared (either mitigating the condition that made the window urgent or merely shutting off the alarm) or the window to be withdrawn.

To set a window's WM_HINTS property, use .

      XSetWMHints
      Display *display
      Window w
      XWMHints *wmhints

display

  Specifies the connection to the X server.

w

  Specifies the window.

wmhints

  Specifies the XWMHints structure to be used.

The function sets the window manager hints that include icon information and location, the initial state of the window, and whether the application relies on the window manager to get keyboard input.

can generate BadAlloc and BadWindow errors.

To read a window's WM_HINTS property, use .

      XWMHints *XGetWMHints
      Display *display
      Window w

display

  Specifies the connection to the X server.

w

  Specifies the window.

The function reads the window manager hints and returns NULL if no WM_HINTS property was set on the window or returns a pointer to an XWMHints structure if it succeeds. When finished with the data, free the space used for it by calling .

can generate a BadWindow error.

### Setting and Reading the WM_NORMAL_HINTS Property

Xlib provides functions that you can use to set or read the WM_NORMAL_HINTS property for a given window. The functions use the flags and the XSizeHints structure, as defined in the `<X11/Xutil.h>`
header file.

The size of the XSizeHints structure may grow in future releases, as new components are added to support new ICCCM features. Passing statically allocated instances of this structure into Xlib may result in memory corruption when running against a future release of the library. As such, it is recommended that only dynamically allocated instances of the structure be used.

To allocate an XSizeHints structure, use `XAllocSizeHints`.

XSizeHints *XAllocSizeHints()

The `XAllocSizeHints` function allocates and returns a pointer to an XSizeHints structure. Note that all fields in the XSizeHints structure are initially set to zero. If insufficient memory is available, `XAllocSizeHints` returns NULL. To free the memory allocated to this structure, use .

The XSizeHints structure contains:

    /* Size hints mask bits */

    #define           USPosition         (1L<<0)  /* user specified x,y */
    #define           USSize             (1L<<1)  /* user specified width,height */
    #define           PPosition          (1L<<2)  /* program specified posistion */
    #define           PSize              (1L<<3)  /* program specified size */
    #define           PMinSize           (1L<<4)  /* program specified minimum size */
    #define           PMaxSize           (1L<<5)  /* program specified maximum size */
    #define           PResizeInc         (1L<<5)  /* program specified resize increments */
    #define           PAspect            (1L<<6)  /* program specified min and max aspect ratios */
    #define           PBaseSize          (1L<<8)
    #define           PWinGravity        (1L<<9)
    #define           PAllHints          (PPosition|Psize|
                                          PMinSize|PMaxSize|
                                          PResizeInc|PAspect)

    /* Values */

    typedef struct {
    	long flags;	        /* marks which fields in this structure are defined */
    	int x, y;	        /* Obsolete */
    	int width, height;	/* Obsolete */
    	int min_width, min_height;
    	int max_width, max_height;
    	int width_inc, height_inc;
    	struct {
    	       int x;	        /* numerator */
    	       int y;	        /* denominator */
    	} min_aspect, max_aspect;
    	int base_width, base_height;
    	int win_gravity;
    	/* this structure may be extended in the future */
    } XSizeHints;

The x, y, width, and height members are now obsolete and are left solely for compatibility reasons. The min_width and min_height members specify the minimum window size that still allows the application to be useful. The max_width and max_height members specify the maximum window size. The width_inc and height_inc members define an arithmetic progression of sizes (minimum to maximum) into which the window prefers to be resized. The min_aspect and max_aspect members are expressed as ratios of x and y, and they allow an application to specify the range of aspect ratios it prefers. The base_width and base_height members define the desired size of the window. The window manager will interpret the position of the window and its border width to position the point of the outer rectangle of the overall window specified by the win_gravity member. The outer rectangle of the window includes any borders or decorations supplied by the window manager. In other words, if the window manager decides to place the window where the client asked, the position on the parent window's border named by the win_gravity will be placed where the client window would have been placed in the absence of a window manager.

Note that use of the PAllHints macro is highly discouraged.

To set a window's WM_NORMAL_HINTS property, use .

      void XSetWMNormalHints
      Display *display
      Window w
      XSizeHints *hints

display

  Specifies the connection to the X server.

w

  Specifies the window.

hints

  Specifies the size hints for the window in its normal state.

The function replaces the size hints for the WM_NORMAL_HINTS property on the specified window. If the property does not already exist, sets the size hints for the WM_NORMAL_HINTS property on the specified window. The property is stored with a type of WM_SIZE_HINTS and a format of 32.

can generate BadAlloc and BadWindow errors.

To read a window's WM_NORMAL_HINTS property, use .

      Status XGetWMNormalHints
      Display *display
      Window w
      XSizeHints *hints_return
      long *supplied_return

display

  Specifies the connection to the X server.

w

  Specifies the window.

hints_return

  Returns the size hints for the window in its normal state.

supplied_return

  Returns the hints that were supplied by the user.

The function returns the size hints stored in the WM_NORMAL_HINTS property on the specified window. If the property is of type WM_SIZE_HINTS, is of format 32, and is long enough to contain either an old (pre-ICCCM) or new size hints structure, sets the various fields of the XSizeHints structure, sets the supplied_return argument to the list of fields that were supplied by the user (whether or not they contained defined values), and returns a nonzero status. Otherwise, it returns a zero status.

If returns successfully and a pre-ICCCM size hints property is read, the supplied_return argument will contain the following bits:

    (USPosition|USSize|PPosition|PSize|PMinSize|
     PMaxSize|PResizeInc|PAspect)

If the property is large enough to contain the base size and window gravity fields as well, the supplied_return argument will also contain the following bits:

    PBaseSize|PWinGravity

can generate a BadWindow error.

To set a window's WM_SIZE_HINTS property, use .

      void XSetWMSizeHints
      Display *display
      Window w
      XSizeHints *hints
      Atom property

display

  Specifies the connection to the X server.

w

  Specifies the window.

hints

  Specifies the XSizeHints structure to be used.

property

  Specifies the property name.

The function replaces the size hints for the specified property on the named window. If the specified property does not already exist, sets the size hints for the specified property on the named window. The property is stored with a type of WM_SIZE_HINTS and a format of 32. To set a window's normal size hints, you can use the function.

can generate BadAlloc, BadAtom, and BadWindow errors.

To read a window's WM_SIZE_HINTS property, use .

      Status XGetWMSizeHints
      Display *display
      Window w
      XSizeHints *hints_return
      long *supplied_return
      Atom property

display

  Specifies the connection to the X server.

w

  Specifies the window.

hints_return

  Returns the XSizeHints structure.

supplied_return

  Returns the hints that were supplied by the user.

property

  Specifies the property name.

The function returns the size hints stored in the specified property on the named window. If the property is of type WM_SIZE_HINTS, is of format 32, and is long enough to contain either an old (pre-ICCCM) or new size hints structure, sets the various fields of the XSizeHints structure, sets the supplied_return argument to the list of fields that were supplied by the user (whether or not they contained defined values), and returns a nonzero status. Otherwise, it returns a zero status. To get a window's normal size hints, you can use the function.

If returns successfully and a pre-ICCCM size hints property is read, the supplied_return argument will contain the following bits:

    (USPosition|USSize|PPosition|PSize|PMinSize|
     PMaxSize|PResizeInc|PAspect)

If the property is large enough to contain the base size and window gravity fields as well, the supplied_return argument will also contain the following bits:

    PBaseSize|PWinGravity

can generate BadAtom and BadWindow errors.

### Setting and Reading the WM_CLASS Property

Xlib provides functions that you can use to set and get the WM_CLASS property for a given window. These functions use the XClassHint structure, which is defined in the `<X11/Xutil.h>`
header file.

To allocate an XClassHint structure, use `XAllocClassHint`.

XClassHint *XAllocClassHint()

The `XAllocClassHint` function allocates and returns a pointer to an XClassHint structure. Note that the pointer fields in the XClassHint structure are initially set to NULL. If insufficient memory is available, `XAllocClassHint` returns NULL. To free the memory allocated to this structure, use .

The XClassHint contains:

    typedef struct {
    	char *res_name;
    	char *res_class;
    } XClassHint;

The res_name member contains the application name, and the res_class member contains the application class. Note that the name set in this property may differ from the name set as WM_NAME. That is, WM_NAME specifies what should be displayed in the title bar and, therefore, can contain temporal information (for example, the name of a file currently in an editor's buffer). On the other hand, the name specified as part of WM_CLASS is the formal name of the application that should be used when retrieving the application's resources from the resource database.

To set a window's WM_CLASS property, use .

      XSetClassHint
      Display *display
      Window w
      XClassHint *class_hints

display

  Specifies the connection to the X server.

w

  Specifies the window.

class_hints

  Specifies the XClassHint structure that is to be used.

The function sets the class hint for the specified window. If the strings are not in the Host Portable Character Encoding, the result is implementation-dependent.

can generate BadAlloc and BadWindow errors.

To read a window's WM_CLASS property, use .

      Status XGetClassHint
      Display *display
      Window w
      XClassHint *class_hints_return

display

  Specifies the connection to the X server.

w

  Specifies the window.

class_hints_return

  Returns the XClassHint structure.

The function returns the class hint of the specified window to the members of the supplied structure. If the data returned by the server is in the Latin Portable Character Encoding, then the returned strings are in the Host Portable Character Encoding. Otherwise, the result is implementation-dependent. It returns a nonzero status on success; otherwise, it returns a zero status. To free res_name and res_class when finished with the strings, use on each individually.

can generate a BadWindow error.

### Setting and Reading the WM_TRANSIENT_FOR Property

Xlib provides functions that you can use to set and read the WM_TRANSIENT_FOR property for a given window.

To set a window's WM_TRANSIENT_FOR property, use .

      XSetTransientForHint
      Display *display
      Window w
      Window prop_window

display

  Specifies the connection to the X server.

w

  Specifies the window.

prop_window

  Specifies the window that the WM_TRANSIENT_FOR property is to be set to.

The function sets the WM_TRANSIENT_FOR property of the specified window to the specified prop_window.

can generate BadAlloc and BadWindow errors.

To read a window's WM_TRANSIENT_FOR property, use .

      Status XGetTransientForHint
      Display *display
      Window w
      Window *prop_window_return

display

  Specifies the connection to the X server.

w

  Specifies the window.

prop_window_return

  Returns the WM_TRANSIENT_FOR property of the specified window.

The function returns the WM_TRANSIENT_FOR property for the specified window. It returns a nonzero status on success; otherwise, it returns a zero status.

can generate a BadWindow error.

### Setting and Reading the WM_PROTOCOLS Property

Xlib provides functions that you can use to set and read the WM_PROTOCOLS property for a given window.

To set a window's WM_PROTOCOLS property, use .

      Status XSetWMProtocols
      Display *display
      Window w
      Atom *protocols
      int count

display

  Specifies the connection to the X server.

w

  Specifies the window.

protocols

  Specifies the list of protocols.

count

  Specifies the number of (Cn.

The function replaces the WM_PROTOCOLS property on the specified window with the list of atoms specified by the protocols argument. If the property does not already exist, sets the WM_PROTOCOLS property on the specified window to the list of atoms specified by the protocols argument. The property is stored with a type of ATOM and a format of 32. If it cannot intern the WM_PROTOCOLS atom, returns a zero status. Otherwise, it returns a nonzero status.

can generate BadAlloc and BadWindow errors.

To read a window's WM_PROTOCOLS property, use .

      Status XGetWMProtocols
      Display *display
      Window w
      Atom **protocols_return
      int *count_return

display

  Specifies the connection to the X server.

w

  Specifies the window.

protocols_return

  Returns the list of protocols.

count_return

  Returns the number of (Cn.

The function returns the list of atoms stored in the WM_PROTOCOLS property on the specified window. These atoms describe window manager protocols in which the owner of this window is willing to participate. If the property exists, is of type ATOM, is of format 32, and the atom WM_PROTOCOLS can be interned, sets the protocols_return argument to a list of atoms, sets the count_return argument to the number of elements in the list, and returns a nonzero status. Otherwise, it sets neither of the return arguments and returns a zero status. To release the list of atoms, use .

can generate a BadWindow error.

### Setting and Reading the WM_COLORMAP_WINDOWS Property

Xlib provides functions that you can use to set and read the WM_COLORMAP_WINDOWS property for a given window.

To set a window's WM_COLORMAP_WINDOWS property, use .

      Status XSetWMColormapWindows
      Display *display
      Window w
      Window *colormap_windows
      int count

display

  Specifies the connection to the X server.

w

  Specifies the window.

colormap_windows

  Specifies the list of windows.

count

  Specifies the number of (Cn.

The function replaces the WM_COLORMAP_WINDOWS property on the specified window with the list of windows specified by the colormap_windows argument. If the property does not already exist, sets the WM_COLORMAP_WINDOWS property on the specified window to the list of windows specified by the colormap_windows argument. The property is stored with a type of WINDOW and a format of 32. If it cannot intern the WM_COLORMAP_WINDOWS atom, returns a zero status. Otherwise, it returns a nonzero status.

can generate BadAlloc and BadWindow errors.

To read a window's WM_COLORMAP_WINDOWS property, use .

      Status XGetWMColormapWindows
      Display *display
      Window w
      Window **colormap_windows_return
      int *count_return

display

  Specifies the connection to the X server.

w

  Specifies the window.

colormap_windows_return

  Returns the list of windows.

count_return

  Returns the number of (Cn.

The function returns the list of window identifiers stored in the WM_COLORMAP_WINDOWS property on the specified window. These identifiers indicate the colormaps that the window manager may need to install for this window. If the property exists, is of type WINDOW, is of format 32, and the atom WM_COLORMAP_WINDOWS can be interned, sets the windows_return argument to a list of window identifiers, sets the count_return argument to the number of elements in the list, and returns a nonzero status. Otherwise, it sets neither of the return arguments and returns a zero status. To release the list of window identifiers, use .

can generate a BadWindow error.

### Setting and Reading the WM_ICON_SIZE Property

Xlib provides functions that you can use to set and read the WM_ICON_SIZE property for a given window. These functions use the XIconSize
structure, which is defined in the `<X11/Xutil.h>`
header file.

To allocate an XIconSize structure, use `XAllocIconSize`.

XIconSize *XAllocIconSize()

The `XAllocIconSize` function allocates and returns a pointer to an XIconSize structure. Note that all fields in the XIconSize structure are initially set to zero. If insufficient memory is available, `XAllocIconSize` returns NULL. To free the memory allocated to this structure, use .

The XIconSize structure contains:

    typedef struct {
    	int min_width, min_height;
    	int max_width, max_height;
    	int width_inc, height_inc;
    } XIconSize;

The width_inc and height_inc members define an arithmetic progression of sizes (minimum to maximum) that represent the supported icon sizes.

To set a window's WM_ICON_SIZE property, use .

      XSetIconSizes
      Display *display
      Window w
      XIconSize *size_list
      int count

display

  Specifies the connection to the X server.

w

  Specifies the window.

size_list

  Specifies the size list.

count

  Specifies the number of items in the size list.

The function is used only by window managers to set the supported icon sizes.

can generate BadAlloc and BadWindow errors.

To read a window's WM_ICON_SIZE property, use .

      Status XGetIconSizes
      Display *display
      Window w
      XIconSize **size_list_return
      int *count_return

display

  Specifies the connection to the X server.

w

  Specifies the window.

size_list_return

  Returns the size list.

count_return

  Returns the number of items in the size list.

The function returns zero if a window manager has not set icon sizes; otherwise, it returns nonzero. should be called by an application that wants to find out what icon sizes would be most appreciated by the window manager under which the application is running. The application should then use to supply the window manager with an icon pixmap or window in one of the supported sizes. To free the data allocated in size_list_return, use .

can generate a BadWindow error.

### Using Window Manager Convenience Functions

The function stores the standard set of window manager properties, with text properties in standard encodings for internationalized text communication. The standard window manager properties for a given window are WM_NAME, WM_ICON_NAME, WM_HINTS, WM_NORMAL_HINTS, WM_CLASS, WM_COMMAND, WM_CLIENT_MACHINE, and WM_LOCALE_NAME.

      void XmbSetWMProperties
      Display *display
      Window w
      char *window_name
      char *icon_name
      char *argv[]
      int argc
      XSizeHints *normal_hints
      XWMHints *wm_hints
      XClassHint *class_hints

display

  Specifies the connection to the X server.

w

  Specifies the window.

window_name

  Specifies the window name, which should be a null-terminated string.

icon_name

  Specifies the icon name, which should be a null-terminated string.

argv

  Specifies the application's argument list.

argc

  Specifies the number of arguments.

hints

  Specifies the size hints for the window in its normal state.

wm_hints

  Specifies the XWMHints structure to be used.

class_hints

  Specifies the XClassHint structure to be used.

The convenience function provides a simple programming interface for setting those essential window properties that are used for communicating with other clients (particularly window and session managers).

If the window_name argument is non-NULL, sets the WM_NAME property. If the icon_name argument is non-NULL, sets the WM_ICON_NAME property. The window_name and icon_name arguments are null-terminated strings in the encoding of the current locale. If the arguments can be fully converted to the STRING encoding, the properties are created with type ``STRING''; otherwise, the arguments are converted to Compound Text, and the properties are created with type ``COMPOUND_TEXT''.

If the normal_hints argument is non-NULL, calls , which sets the WM_NORMAL_HINTS property (see section 14.1.7). If the wm_hints argument is non-NULL, calls , which sets the WM_HINTS property (see section 14.1.6).

If the argv argument is non-NULL, sets the WM_COMMAND property from argv and argc. An argc of zero indicates a zero-length command.

The hostname of the machine is stored using (see section 14.2.2).

If the class_hints argument is non-NULL, sets the WM_CLASS property. If the res_name member in the XClassHint structure is set to the NULL pointer and the RESOURCE_NAME environment variable is set, the value of the environment variable is substituted for res_name. If the res_name member is NULL, the environment variable is not set, and argv and argv[0] are set, then the value of argv[0], stripped of any directory prefixes, is substituted for res_name.

It is assumed that the supplied class_hints.res_name and argv, the RESOURCE_NAME environment variable, and the hostname of the machine are in the encoding of the locale announced for the LC_CTYPE category (on POSIX-compliant systems, the LC_CTYPE, else LANG environment variable). The corresponding WM_CLASS, WM_COMMAND, and WM_CLIENT_MACHINE properties are typed according to the local host locale announcer. No encoding conversion is performed prior to storage in the properties.

For clients that need to process the property text in a locale, sets the WM_LOCALE_NAME property to be the name of the current locale. The name is assumed to be in the Host Portable Character Encoding and is converted to STRING for storage in the property.

can generate BadAlloc and BadWindow errors.

To set a window's standard window manager properties with strings in client-specified encodings, use . The standard window manager properties for a given window are WM_NAME, WM_ICON_NAME, WM_HINTS, WM_NORMAL_HINTS, WM_CLASS, WM_COMMAND, and WM_CLIENT_MACHINE.

      void XSetWMProperties
      Display *display
      Window w
      XTextProperty *window_name
      XTextProperty *icon_name
      char **argv
      int argc
      XSizeHints *normal_hints
      XWMHints *wm_hints
      XClassHint *class_hints

display

  Specifies the connection to the X server.

w

  Specifies the window.

window_name

  Specifies the window name, which should be a null-terminated string.

icon_name

  Specifies the icon name, which should be a null-terminated string.

argv

  Specifies the application's argument list.

argc

  Specifies the number of arguments.

normal_hints

  Specifies the size hints for the window in its normal state.

wm_hints

  Specifies the XWMHints structure to be used.

class_hints

  Specifies the XClassHint structure to be used.

The convenience function provides a single programming interface for setting those essential window properties that are used for communicating with other clients (particularly window and session managers).

If the window_name argument is non-NULL, calls , which, in turn, sets the WM_NAME property (see section 14.1.4). If the icon_name argument is non-NULL, calls , which sets the WM_ICON_NAME property (see section 14.1.5). If the argv argument is non-NULL, calls , which sets the WM_COMMAND property (see section 14.2.1). Note that an argc of zero is allowed to indicate a zero-length command. Note also that the hostname of this machine is stored using (see section 14.2.2).

If the normal_hints argument is non-NULL, calls , which sets the WM_NORMAL_HINTS property (see section 14.1.7). If the wm_hints argument is non-NULL, calls , which sets the WM_HINTS property (see section 14.1.6).

If the class_hints argument is non-NULL, calls , which sets the WM_CLASS property (see section 14.1.8). If the res_name member in the XClassHint structure is set to the NULL pointer and the RESOURCE_NAME environment variable is set, then the value of the environment variable is substituted for res_name. If the res_name member is NULL, the environment variable is not set, and argv and argv[0] are set, then the value of argv[0], stripped of any directory prefixes, is substituted for res_name.

can generate BadAlloc and BadWindow errors.

## Client to Session Manager Communication

This section discusses how to:

- Set and read the WM_COMMAND property

- Set and read the WM_CLIENT_MACHINE property

### Setting and Reading the WM_COMMAND Property

Xlib provides functions that you can use to set and read the WM_COMMAND property for a given window.

To set a window's WM_COMMAND property, use .

      XSetCommand
      Display *display
      Window w
      char **argv
      int argc

display

  Specifies the connection to the X server.

w

  Specifies the window.

argv

  Specifies the application's argument list.

argc

  Specifies the number of arguments.

The function sets the command and arguments used to invoke the application. (Typically, argv is the argv array of your main program.) If the strings are not in the Host Portable Character Encoding, the result is implementation-dependent.

can generate BadAlloc and BadWindow errors.

To read a window's WM_COMMAND property, use .

      Status XGetCommand
      Display *display
      Window w
      char ***argv_return
      int *argc_return

display

  Specifies the connection to the X server.

w

  Specifies the window.

argv_return

  Returns the application's argument list.

argc_return

  Returns the number of arguments returned.

The function reads the WM_COMMAND property from the specified window and returns a string list. If the WM_COMMAND property exists, it is of type STRING and format 8. If sufficient memory can be allocated to contain the string list, fills in the argv_return and argc_return arguments and returns a nonzero status. Otherwise, it returns a zero status. If the data returned by the server is in the Latin Portable Character Encoding, then the returned strings are in the Host Portable Character Encoding. Otherwise, the result is implementation-dependent. To free the memory allocated to the string list, use .

### Setting and Reading the WM_CLIENT_MACHINE Property

Xlib provides functions that you can use to set and read the WM_CLIENT_MACHINE property for a given window.

To set a window's WM_CLIENT_MACHINE property, use .

      void XSetWMClientMachine
      Display *display
      Window w
      XTextProperty *text_prop

display

  Specifies the connection to the X server.

w

  Specifies the window.

text_prop

  Specifies the XTextProperty structure to be used.

The convenience function calls to set the WM_CLIENT_MACHINE property.

To read a window's WM_CLIENT_MACHINE property, use .

      Status XGetWMClientMachine
      Display *display
      Window w
      XTextProperty *text_prop_return

display

  Specifies the connection to the X server.

w

  Specifies the window.

text_prop_return

  Returns the XTextProperty structure.

The convenience function performs an on the WM_CLIENT_MACHINE property. It returns a nonzero status on success; otherwise, it returns a zero status.

## Standard Colormaps

Applications with color palettes, smooth-shaded drawings, or digitized images demand large numbers of colors. In addition, these applications often require an efficient mapping from color triples to pixel values that display the appropriate colors.

As an example, consider a three-dimensional display program that wants to draw a smoothly shaded sphere. At each pixel in the image of the sphere, the program computes the intensity and color of light reflected back to the viewer. The result of each computation is a triple of red, green, and blue (RGB) coefficients in the range 0.0 to 1.0. To draw the sphere, the program needs a colormap that provides a large range of uniformly distributed colors. The colormap should be arranged so that the program can convert its RGB triples into pixel values very quickly, because drawing the entire sphere requires many such conversions.

On many current workstations, the display is limited to 256 or fewer colors. Applications must allocate colors carefully, not only to make sure they cover the entire range they need but also to make use of as many of the available colors as possible. On a typical X display, many applications are active at once. Most workstations have only one hardware look-up table for colors, so only one application colormap can be installed at a given time. The application using the installed colormap is displayed correctly, and the other applications go technicolor and are displayed with false colors.

As another example, consider a user who is running an image processing program to display earth-resources data. The image processing program needs a colormap set up with 8 reds, 8 greens, and 4 blues, for a total of 256 colors. Because some colors are already in use in the default colormap, the image processing program allocates and installs a new colormap.

The user decides to alter some of the colors in the image by invoking a color palette program to mix and choose colors. The color palette program also needs a colormap with eight reds, eight greens, and four blues, so just like the image processing program, it must allocate and install a new colormap.

Because only one colormap can be installed at a time, the color palette may be displayed incorrectly whenever the image processing program is active. Conversely, whenever the palette program is active, the image may be displayed incorrectly. The user can never match or compare colors in the palette and image. Contention for colormap resources can be reduced if applications with similar color needs share colormaps.

The image processing program and the color palette program could share the same colormap if there existed a convention that described how the colormap was set up. Whenever either program was active, both would be displayed correctly.

The standard colormap properties define a set of commonly used colormaps. Applications that share these colormaps and conventions display true colors more often and provide a better interface to the user.

Standard colormaps allow applications to share commonly used color resources. This allows many applications to be displayed in true colors simultaneously, even when each application needs an entirely filled colormap.

Several standard colormaps are described in this section. Usually, a window manager creates these colormaps. Applications should use the standard colormaps if they already exist.

To allocate an XStandardColormap structure, use `XAllocStandardColormap`.

XStandardColormap *XAllocStandardColormap()

The `XAllocStandardColormap` function allocates and returns a pointer to an XStandardColormap structure. Note that all fields in the XStandardColormap structure are initially set to zero. If insufficient memory is available, `XAllocStandardColormap` returns NULL. To free the memory allocated to this structure, use .

The XStandardColormap structure contains:

    /* Hints */

    #define       ReeaseByFreeingColormap  ((XID)1L)

    /* Values */

    typedef struct {
    	Colormap colormap;
    	unsigned long red_max;
    	unsigned long red_mult;
    	unsigned long green_max;
    	unsigned long green_mult;
    	unsigned long blue_max;
    	unsigned long blue_mult;
    	unsigned long base_pixel;
    	VisualID visualid;
    	XID killid;
    } XStandardColormap;

The colormap member is the colormap created by the function. The red_max, green_max, and blue_max members give the maximum red, green, and blue values, respectively. Each color coefficient ranges from zero to its max, inclusive. For example, a common colormap allocation is 3/3/2 (3 planes for red, 3 planes for green, and 2 planes for blue). This colormap would have red_max = 7, green_max = 7, and blue_max = 3. An alternate allocation that uses only 216 colors is red_max = 5, green_max = 5, and blue_max = 5.

The red_mult, green_mult, and blue_mult members give the scale factors used to compose a full pixel value. (See the discussion of the base_pixel members for further information.) For a 3/3/2 allocation, red_mult might be 32, green_mult might be 4, and blue_mult might be 1. For a 6-colors-each allocation, red_mult might be 36, green_mult might be 6, and blue_mult might be 1.

The base_pixel member gives the base pixel value used to compose a full pixel value. Usually, the base_pixel is obtained from a call to the function. Given integer red, green, and blue coefficients in their appropriate ranges, one then can compute a corresponding pixel value by using the following expression:

    (r * red_mult + g * green_mult + b * blue_mult + base_pixel) & 0xFFFFFFFF

For GrayScale colormaps, only the colormap, red_max, red_mult, and base_pixel members are defined. The other members are ignored. To compute a GrayScale pixel value, use the following expression:

    (gray * red_mult + base_pixel) & 0xFFFFFFFF

Negative multipliers can be represented by converting the 2's complement representation of the multiplier into an unsigned long and storing the result in the appropriate _mult field. The step of masking by 0xFFFFFFFF effectively converts the resulting positive multiplier into a negative one. The masking step will take place automatically on many machine architectures, depending on the size of the integer type used to do the computation.

The visualid member gives the ID number of the visual from which the colormap was created. The killid member gives a resource ID that indicates whether the cells held by this standard colormap are to be released by freeing the colormap ID or by calling the function on the indicated resource. (Note that this method is necessary for allocating out of an existing colormap.)

The properties containing the XStandardColormap information have the type RGB_COLOR_MAP.

The remainder of this section discusses standard colormap properties and atoms as well as how to manipulate standard colormaps.

### Standard Colormap Properties and Atoms

Several standard colormaps are available. Each standard colormap is defined by a property, and each such property is identified by an atom. The following list names the atoms and describes the colormap associated with each one. The `<X11/Xatom.h>`
header file contains the definitions for each of the following atoms, which are prefixed with XA_.

RGB_DEFAULT_MAP

  This atom names a property. The value of the property is an array of XStandardColormap structures. Each entry in the array describes an RGB subset of the default color map for the Visual specified by visual_id.

  Some applications only need a few RGB colors and may be able to allocate them from the system default colormap. This is the ideal situation because the fewer colormaps that are active in the system the more applications are displayed with correct colors at all times.

  A typical allocation for the RGB_DEFAULT_MAP on 8-plane displays is 6 reds, 6 greens, and 6 blues. This gives 216 uniformly distributed colors (6 intensities of 36 different hues) and still leaves 40 elements of a 256-element colormap available for special-purpose colors for text, borders, and so on.

RGB_BEST_MAP

  This atom names a property. The value of the property is an XStandardColormap.

  The property defines the best RGB colormap available on the screen. (Of course, this is a subjective evaluation.) Many image processing and three-dimensional applications need to use all available colormap cells and to distribute as many perceptually distinct colors as possible over those cells. This implies that there may be more green values available than red, as well as more green or red than blue.

  For an 8-plane PseudoColor visual, RGB_BEST_MAP is likely to be a 3/3/2 allocation. For a 24-plane DirectColor visual, RGB_BEST_MAP is normally an 8/8/8 allocation.

RGB_RED_MAP,RGB_GREEN_MAP,RGB_BLUE_MAP

  These atoms name properties. The value of each property is an XStandardColormap.

  The properties define all-red, all-green, and all-blue colormaps, respectively. These maps are used by applications that want to make color-separated images. For example, a user might generate a full-color image on an 8-plane display both by rendering an image three times (once with high color resolution in red, once with green, and once with blue) and by multiply exposing a single frame in a camera.

RGB_GRAY_MAP

  This atom names a property. The value of the property is an XStandardColormap.

  The property describes the best GrayScale colormap available on the screen. As previously mentioned, only the colormap, red_max, red_mult, and base_pixel members of the XStandardColormap structure are used for GrayScale colormaps.

### Setting and Obtaining Standard Colormaps

Xlib provides functions that you can use to set and obtain an XStandardColormap structure.

To set an XStandardColormap structure, use .

      void XSetRGBColormaps
      Display *display
      Window w
      XStandardColormap *std_colormap
      int count
      Atom property

display

  Specifies the connection to the X server.

w

  Specifies the window.

std_colormap

  Specifies the XStandardColormap structure to be used.

count

  Specifies the number of (Cn.

property

  Specifies the property name.

The function replaces the RGB colormap definition in the specified property on the named window. If the property does not already exist, sets the RGB colormap definition in the specified property on the named window. The property is stored with a type of RGB_COLOR_MAP and a format of 32. Note that it is the caller's responsibility to honor the ICCCM restriction that only RGB_DEFAULT_MAP contain more than one definition.

The function usually is only used by window or session managers. To create a standard colormap, follow this procedure:

- Open a new connection to the same server.

- Grab the server.

- See if the property is on the property list of the root window for the screen.

- If the desired property is not present:

- Create a colormap (unless you are using the default colormap of the screen).

- Determine the color characteristics of the visual.

- Allocate cells in the colormap (or create it with AllocAll).

- Call to store appropriate color values in the colormap.

- Fill in the descriptive members in the XStandardColormap structure.

- Attach the property to the root window.

- Use to make the resource permanent.

- Ungrab the server.

can generate BadAlloc, BadAtom, and BadWindow errors.

To obtain the XStandardColormap structure associated with the specified property, use .

      Status XGetRGBColormaps
      Display *display
      Window w
      XStandardColormap **std_colormap_return
      int *count_return
      Atom property

display

  Specifies the connection to the X server.

w

  Specifies the window.

std_colormap_return

  Returns the XStandardColormap structure.

count_return

  Returns the number of (Cn.

property

  Specifies the property name.

The function returns the RGB colormap definitions stored in the specified property on the named window. If the property exists, is of type RGB_COLOR_MAP, is of format 32, and is long enough to contain a colormap definition, allocates and fills in space for the returned colormaps and returns a nonzero status. If the visualid is not present, assumes the default visual for the screen on which the window is located; if the killid is not present, None is assumed, which indicates that the resources cannot be released. Otherwise, none of the fields are set, and returns a zero status. Note that it is the caller's responsibility to honor the ICCCM restriction that only RGB_DEFAULT_MAP contain more than one definition.

can generate BadAtom and BadWindow errors.