After you connect the display to the X server and create a window, you can use the Xlib window information functions to: Obtain information about a window Translate screen coordinates Manipulate property lists Obtain and change window properties Manipulate selections Xlib provides functions that you can use to obtain information about the window tree, the window's current attributes, the window's current geometry, or the current pointer coordinates. Because they are most frequently used by window managers, these functions all return a status to indicate whether the window still exists. To obtain the parent, a list of children, and number of children for a given window, use . Child Window Parent Window XQueryTree Status XQueryTree Display *display Window w Window *root_return Window *parent_return Window **children_return unsignedint *nchildren_return display Specifies the connection to the X server. you want to obtain w Specifies the window (Wi. root_return Returns the root window. parent_return Returns the parent window. children_return Returns the list of children. nchildren_return Returns the number of children. The function returns the root ID, the parent window ID, a pointer to the list of children windows (NULL when there are no children), and the number of children in the list for the specified window. The children are listed in current stacking order, from bottom-most (first) to top-most (last). returns zero if it fails and nonzero if it succeeds. To free a non-NULL children list when it is no longer needed, use . can generate a BadWindow error. To obtain the current attributes of a given window, use . XGetWindowAttributes Status XGetWindowAttributes Display *display Window w XWindowAttributes *window_attributes_return display Specifies the connection to the X server. w Specifies the window (Wi. window_attributes_return Returns the specified window's attributes in the XWindowAttributes structure. The function returns the current attributes for the specified window to an XWindowAttributes structure. XWindowAttributes typedef struct { int x, y; /* location of window */ int width, height; /* width and height of window */ int border_width; /* border width of window */ int depth; /* depth of window */ Visual *visual; /* the associated visual structure */ Window root; /* root of screen containing window */ int class; /* InputOutput, InputOnly*/ int bit_gravity; /* one of the bit gravity values */ int win_gravity; /* one of the window gravity values */ int backing_store; /* NotUseful, WhenMapped, Always */ unsigned long backing_planes; /* planes to be preserved if possible */ unsigned long backing_pixel; /* value to be used when restoring planes */ Bool save_under; /* boolean, should bits under be saved? */ Colormap colormap; /* color map to be associated with window */ Bool map_installed; /* boolean, is color map currently installed*/ int map_state; /* IsUnmapped, IsUnviewable, IsViewable */ long all_event_masks; /* set of events all people have interest in*/ long your_event_mask; /* my event mask */ long do_not_propagate_mask; /* set of events that should not propagate */ Bool override_redirect; /* boolean value for override-redirect */ Screen *screen; /* back pointer to correct screen */ } XWindowAttributes; The x and y members are set to the upper-left outer corner relative to the parent window's origin. The width and height members are set to the inside size of the window, not including the border. The border_width member is set to the window's border width in pixels. The depth member is set to the depth of the window (that is, bits per pixel for the object). The visual member is a pointer to the screen's associated Visual structure. The root member is set to the root window of the screen containing the window. The class member is set to the window's class and can be either InputOutput or InputOnly. The bit_gravity member is set to the window's bit gravity and can be one of the following: ForgetGravity NorthWestGravity NorthGravity NorthEastGravity WestGravity EastGravity SouthWestGravity SouthGravity SouthEastGravity StaticGravity The win_gravity member is set to the window's window gravity and can be one of the following: UnmapGravity NorthWestGravity NorthGravity NorthEastGravity WestGravity EastGravity SouthWestGravity SouthGravity SouthEastGravity StaticGravity CenterGravity For additional information on gravity, see section 3.2.3. The backing_store member is set to indicate how the X server should maintain the contents of a window and can be WhenMapped, Always, or NotUseful. The backing_planes member is set to indicate (with bits set to 1) which bit planes of the window hold dynamic data that must be preserved in backing_stores and during save_unders. The backing_pixel member is set to indicate what values to use for planes not set in backing_planes. The save_under member is set to True or False. The colormap member is set to the colormap for the specified window and can be a colormap ID or None. The map_installed member is set to indicate whether the colormap is currently installed and can be True or False. The map_state member is set to indicate the state of the window and can be IsUnmapped, IsUnviewable, or IsViewable. IsUnviewable is used if the window is mapped but some ancestor is unmapped. The all_event_masks member is set to the bitwise inclusive OR of all event masks selected on the window by all clients. The your_event_mask member is set to the bitwise inclusive OR of all event masks selected by the querying client. The do_not_propagate_mask member is set to the bitwise inclusive OR of the set of events that should not propagate. The override_redirect member is set to indicate whether this window overrides structure control facilities and can be True or False. Window manager clients should ignore the window if this member is True. The screen member is set to a screen pointer that gives you a back pointer to the correct screen. This makes it easier to obtain the screen information without having to loop over the root window fields to see which field matches. can generate BadDrawable and BadWindow errors. To obtain the current geometry of a given drawable, use . XGetGeometry Status XGetGeometry Display *display Drawable d Window *root_return int*x_return, *y_return unsignedint*width_return, *height_return unsignedint *border_width_return unsignedint *depth_return display Specifies the connection to the X server. d Specifies the drawable(Dr. root_return Returns the root window. x_return y_return Return the x and y coordinates that define the location of the drawable. For a window, these coordinates specify the upper-left outer corner relative to its parent's origin. For pixmaps, these coordinates are always zero. width_return height_return Return the drawable's dimensions (width and height). For a window, these dimensions specify the inside size, not including the border. border_width_return Returns the border width in pixels. If the drawable is a pixmap, it returns zero. depth_return Returns the depth of the drawable (bits per pixel for the object). The function returns the root window and the current geometry of the drawable. The geometry of the drawable includes the x and y coordinates, width and height, border width, and depth. These are described in the argument list. It is legal to pass to this function a window whose class is InputOnly. can generate a BadDrawable error. Applications sometimes need to perform a coordinate transformation from the coordinate space of one window to another window or need to determine which window the pointing device is in. and fulfill these needs (and avoid any race conditions) by asking the X server to perform these operations. To translate a coordinate in one window to the coordinate space of another window, use . XTranslateCoordinates Bool XTranslateCoordinates Display *display Windowsrc_w, dest_w intsrc_x, src_y int*dest_x_return, *dest_y_return Window *child_return display Specifies the connection to the X server. src_w Specifies the source window. dest_w Specifies the destination window. src_x src_y Specify the x and y coordinates within the source window. dest_x_return dest_y_return Return the x and y coordinates within the destination window. child_return Returns the child if the coordinates are contained in a mapped child of the destination window. If returns True, it takes the src_x and src_y coordinates relative to the source window's origin and returns these coordinates to dest_x_return and dest_y_return relative to the destination window's origin. If returns False, src_w and dest_w are on different screens, and dest_x_return and dest_y_return are zero. If the coordinates are contained in a mapped child of dest_w, that child is returned to child_return. Otherwise, child_return is set to None. can generate a BadWindow error. To obtain the screen coordinates of the pointer or to determine the pointer coordinates relative to a specified window, use . XQueryPointer Bool XQueryPointer Display *display Window w Window*root_return, *child_return int*root_x_return, *root_y_return int*win_x_return, *win_y_return unsignedint *mask_return display Specifies the connection to the X server. w Specifies the window. root_return Returns the root window (Ro. child_return Returns the child window that the pointer is located in, if any. root_x_return root_y_return Return the pointer coordinates relative to the root window's origin. win_x_return win_y_return Return the pointer coordinates relative to the specified window. mask_return Returns the current state of the modifier keys and pointer buttons. The function returns the root window the pointer is logically on and the pointer coordinates relative to the root window's origin. If returns False, the pointer is not on the same screen as the specified window, and returns None to child_return and zero to win_x_return and win_y_return. If returns True, the pointer coordinates returned to win_x_return and win_y_return are relative to the origin of the specified window. In this case, returns the child that contains the pointer, if any, or else None to child_return. returns the current logical state of the keyboard buttons and the modifier keys in mask_return. It sets mask_return to the bitwise inclusive OR of one or more of the button or modifier key bitmasks to match the current state of the mouse buttons and the modifier keys. Note that the logical state of a device (as seen through Xlib) may lag the physical state if device event processing is frozen (see section 12.1). can generate a BadWindow error. A property is a collection of named, typed data. The window system has a set of predefined properties Atompredefined (for example, the name of a window, size hints, and so on), and users can define any other arbitrary information and associate it with windows. Each property has a name, which is an ISO Latin-1 string. For each named property, a unique identifier (atom) is associated with it. A property also has a type, for example, string or integer. These types are also indicated using atoms, so arbitrary new types can be defined. Data of only one type may be associated with a single property name. Clients can store and retrieve properties associated with windows. For efficiency reasons, an atom is used rather than a character string. can be used to obtain the atom for property names. Atom A property is also stored in one of several possible formats. The X server can store the information as 8-bit quantities, 16-bit quantities, or 32-bit quantities. This permits the X server to present the data in the byte order that the client expects. If you define further properties of complex type, you must encode and decode them yourself. These functions must be carefully written if they are to be portable. For further information about how to write a library extension, see appendix C. The type of a property is defined by an atom, which allows for arbitrary extension in this type scheme. Atom Certain property names are predefined in the server for commonly used functions. The atoms for these properties are defined in <X11/Xatom.h>. X11/Xatom.h Files<X11/Xatom.h> Headers<X11/Xatom.h> To avoid name clashes with user symbols, the #define name for each atom has the XA_ prefix. For an explanation of the functions that let you get and set much of the information stored in these predefined properties, see chapter 14. The core protocol imposes no semantics on these property names, but semantics are specified in other X Consortium standards, such as the Inter-Client Communication Conventions Manual and the X Logical Font Description Conventions. You can use properties to communicate other information between applications. The functions described in this section let you define new properties and get the unique atom IDs in your applications. Although any particular atom can have some client interpretation within each of the name spaces, atoms occur in five distinct name spaces within the protocol: Selections Property names Property types Font properties Type of a ClientMessage event (none are built into the X server) The built-in selection property names are: PRIMARY SECONDARY The built-in property names are: CUT_BUFFER0 CUT_BUFFER1 CUT_BUFFER2 CUT_BUFFER3 CUT_BUFFER4 CUT_BUFFER5 CUT_BUFFER6 CUT_BUFFER7 RGB_BEST_MAP RGB_BLUE_MAP RGB_DEFAULT_MAP RGB_GRAY_MAP RGB_GREEN_MAP RGB_RED_MAP RESOURCE_MANAGER WM_CLASS WM_CLIENT_MACHINE WM_COLORMAP_WINDOWS WM_COMMAND WM_HINTS WM_ICON_NAME WM_ICON_SIZE WM_NAME WM_NORMAL_HINTS WM_PROTOCOLS WM_STATE WM_TRANSIENT_FOR WM_ZOOM_HINTS The built-in property types are: ARC ATOM BITMAP CARDINAL COLORMAP CURSOR DRAWABLE FONT INTEGER PIXMAP POINT RGB_COLOR_MAP RECTANGLE STRING VISUALID WINDOW WM_HINTS WM_SIZE_HINTS The built-in font property names are: MIN_SPACE NORM_SPACE MAX_SPACE END_SPACE SUPERSCRIPT_X SUPERSCRIPT_Y SUBSCRIPT_X SUBSCRIPT_Y UNDERLINE_POSITION UNDERLINE_THICKNESS FONT_NAME FULL_NAME STRIKEOUT_DESCENT STRIKEOUT_ASCENT ITALIC_ANGLE X_HEIGHT QUAD_WIDTH WEIGHT POINT_SIZE RESOLUTION COPYRIGHT NOTICE FAMILY_NAME CAP_HEIGHT For further information about font properties, see section 8.5. To return an atom for a given name, use . Atominterning XInternAtom Atom XInternAtom Display *display char *atom_name Bool only_if_exists display Specifies the connection to the X server. atom_name Specifies the name associated with the atom you want returned. only_if_exists Specifies a Boolean value that indicates whether the atom must be created. The function returns the atom identifier associated with the specified atom_name string. If only_if_exists is False, the atom is created if it does not exist. Therefore, can return None. If the atom name is not in the Host Portable Character Encoding, the result is implementation-dependent. Uppercase and lowercase matter; the strings ``thing'', ``Thing'', and ``thinG'' all designate different atoms. The atom will remain defined even after the client's connection closes. It will become undefined only when the last connection to the X server closes. can generate BadAlloc and BadValue errors. To return atoms for an array of names, use . Atominterning XInternAtoms Status XInternAtoms Display *display char **names int count Bool only_if_exists Atom *atoms_return display Specifies the connection to the X server. names Specifies the array of atom names. count Specifies the number of (Cn. only_if_exists Specifies a Boolean value that indicates whether the atom must be created. atoms_return Returns the atoms. The function returns the atom identifiers associated with the specified names. The atoms are stored in the atoms_return array supplied by the caller. Calling this function is equivalent to calling for each of the names in turn with the specified value of only_if_exists, but this function minimizes the number of round-trip protocol exchanges between the client and the X server. This function returns a nonzero status if atoms are returned for all of the names; otherwise, it returns zero. can generate BadAlloc and BadValue errors. To return a name for a given atom identifier, use . Atomgetting name XGetAtomName char *XGetAtomName Display *display Atom atom display Specifies the connection to the X server. atom Specifies the atom for the property name you want returned. The function returns the name associated with the specified atom. 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. To free the resulting string, call . can generate a BadAtom error. To return the names for an array of atom identifiers, use . Atomgetting name XGetAtomNames Status XGetAtomNames Display *display Atom *atoms int count char **names_return display Specifies the connection to the X server. atoms Specifies the array of atoms. count Specifies the number of (Cn. names_return Returns the atom names. The function returns the names associated with the specified atoms. The names are stored in the names_return array supplied by the caller. Calling this function is equivalent to calling for each of the atoms in turn, but this function minimizes the number of round-trip protocol exchanges between the client and the X server. This function returns a nonzero status if names are returned for all of the atoms; otherwise, it returns zero. can generate a BadAtom error. You can attach a property list to every window. Each property has a name, a type, and a value (see section 4.3). The value is an array of 8-bit, 16-bit, or 32-bit quantities, whose interpretation is left to the clients. The type char is used to represent 8-bit quantities, the type short is used to represent 16-bit quantities, and the type long is used to represent 32-bit quantities. Xlib provides functions that you can use to obtain, change, update, or interchange window properties. In addition, Xlib provides other utility functions for inter-client communication (see chapter 14). To obtain the type, format, and value of a property of a given window, use . Propertygetting XGetWindowProperty int XGetWindowProperty display w property long_offset long_length delete req_type actual_type_return actual_format_return nitems_return bytes_after_return .br prop_return display Specifies the connection to the X server. w Specifies the window (Wi. property Specifies the property name. long_offset Specifies the offset in the specified property (in 32-bit quantities) where the data is to be retrieved. long_length Specifies the length in 32-bit multiples of the data to be retrieved. delete Specifies a Boolean value that determines whether the property is deleted. req_type Specifies the atom identifier associated with the property type or AnyPropertyType. actual_type_return Returns the atom identifier that defines the actual type of the property. actual_format_return Returns the actual format of the property. nitems_return Returns the actual number of 8-bit, 16-bit, or 32-bit items stored in the prop_return data. bytes_after_return Returns the number of bytes remaining to be read in the property if a partial read was performed. prop_return Returns the data in the specified format. The function returns the actual type of the property; the actual format of the property; the number of 8-bit, 16-bit, or 32-bit items transferred; the number of bytes remaining to be read in the property; and a pointer to the data actually returned. sets the return arguments as follows: If the specified property does not exist for the specified window, returns None to actual_type_return and the value zero to actual_format_return and bytes_after_return. The nitems_return argument is empty. In this case, the delete argument is ignored. If the specified property exists but its type does not match the specified type, returns the actual property type to actual_type_return, the actual property format (never zero) to actual_format_return, and the property length in bytes (even if the actual_format_return is 16 or 32) to bytes_after_return. It also ignores the delete argument. The nitems_return argument is empty. If the specified property exists and either you assign AnyPropertyType to the req_type argument or the specified type matches the actual property type, returns the actual property type to actual_type_return and the actual property format (never zero) to actual_format_return. It also returns a value to bytes_after_return and nitems_return, by defining the following values: N = actual length of the stored property in bytes (even if the format is 16 or 32) I = 4 * long_offset T = N - I L = MINIMUM(T, 4 * long_length) A = N - (I + L) The returned value starts at byte index I in the property (indexing from zero), and its length in bytes is L. If the value for long_offset causes L to be negative, a BadValue error results. The value of bytes_after_return is A, giving the number of trailing unread bytes in the stored property. If the returned format is 8, the returned data is represented as a char array. If the returned format is 16, the returned data is represented as a short array and should be cast to that type to obtain the elements. If the returned format is 32, the returned data is represented as a long array and should be cast to that type to obtain the elements. always allocates one extra byte in prop_return (even if the property is zero length) and sets it to zero so that simple properties consisting of characters do not have to be copied into yet another string before use. If delete is True and bytes_after_return is zero, deletes the property from the window and generates a PropertyNotify event on the window. The function returns Success if it executes successfully. To free the resulting data, use . can generate BadAtom, BadValue, and BadWindow errors. To obtain a given window's property list, use . Propertylisting XListProperties Atom *XListProperties Display *display Window w int *num_prop_return display Specifies the connection to the X server. w Specifies the window (Wi. num_prop_return Returns the length of the properties array. The function returns a pointer to an array of atom properties that are defined for the specified window or returns NULL if no properties were found. To free the memory allocated by this function, use . can generate a BadWindow error. To change a property of a given window, use . Propertychanging Propertyappending Propertyprepending Propertyreplacing Propertyformat Propertytype XChangeProperty XChangeProperty Display *display Window w Atomproperty, type int format int mode unsignedchar *data int nelements display Specifies the connection to the X server. w Specifies the window (Wi. property Specifies the property name. type Specifies the type of the property. The X server does not interpret the type but simply passes it back to an application that later calls . format Specifies whether the data should be viewed as a list of 8-bit, 16-bit, or 32-bit quantities. Possible values are 8, 16, and 32. This information allows the X server to correctly perform byte-swap operations as necessary. If the format is 16-bit or 32-bit, you must explicitly cast your data pointer to an (unsigned char *) in the call to . mode Specifies the mode of the operation. You can pass PropModeReplace, PropModePrepend, or PropModeAppend. data Specifies the property data. nelements Specifies the number of elements of the specified data format. The function alters the property for the specified window and causes the X server to generate a PropertyNotify event on that window. performs the following: If mode is PropModeReplace, discards the previous property value and stores the new data. If mode is PropModePrepend or PropModeAppend, inserts the specified data before the beginning of the existing data or onto the end of the existing data, respectively. The type and format must match the existing property value, or a BadMatch error results. If the property is undefined, it is treated as defined with the correct type and format with zero-length data. If the specified format is 8, the property data must be a char array. If the specified format is 16, the property data must be a short array. If the specified format is 32, the property data must be a long array. The lifetime of a property is not tied to the storing client. Properties remain until explicitly deleted, until the window is destroyed, or until the server resets. For a discussion of what happens when the connection to the X server is closed, see section 2.6. The maximum size of a property is server dependent and can vary dynamically depending on the amount of memory the server has available. (If there is insufficient space, a BadAlloc error results.) can generate BadAlloc, BadAtom, BadMatch, BadValue, and BadWindow errors. To rotate a window's property list, use . XRotateWindowProperties XRotateWindowProperties Display *display Window w Atom properties[] int num_prop int npositions display Specifies the connection to the X server. w Specifies the window. properties Specifies the array of properties that are to be rotated. num_prop Specifies the length of the properties array. npositions Specifies the rotation amount. The function allows you to rotate properties on a window and causes the X server to generate PropertyNotify events. If the property names in the properties array are viewed as being numbered starting from zero and if there are num_prop property names in the list, then the value associated with property name I becomes the value associated with property name (I + npositions) mod N for all I from zero to N − 1. The effect is to rotate the states by npositions places around the virtual ring of property names (right for positive npositions, left for negative npositions). If npositions mod N is nonzero, the X server generates a PropertyNotify event for each property in the order that they are listed in the array. If an atom occurs more than once in the list or no property with that name is defined for the window, a BadMatch error results. If a BadAtom or BadMatch error results, no properties are changed. can generate BadAtom, BadMatch, and BadWindow errors. To delete a property on a given window, use . Propertydeleting XDeleteProperty XDeleteProperty Display *display Window w Atom property display Specifies the connection to the X server. w Specifies the window (Wi. property Specifies the property name. The function deletes the specified property only if the property was defined on the specified window and causes the X server to generate a PropertyNotify event on the window unless the property does not exist. can generate BadAtom and BadWindow errors. Selection Selections are one method used by applications to exchange data. By using the property mechanism, applications can exchange data of arbitrary types and can negotiate the type of the data. A selection can be thought of as an indirect property with a dynamic type. That is, rather than having the property stored in the X server, the property is maintained by some client (the owner). A selection is global in nature (considered to belong to the user but be maintained by clients) rather than being private to a particular window subhierarchy or a particular set of clients. Xlib provides functions that you can use to set, get, or request conversion of selections. This allows applications to implement the notion of current selection, which requires that notification be sent to applications when they no longer own the selection. Applications that support selection often highlight the current selection and so must be informed when another application has acquired the selection so that they can unhighlight the selection. When a client asks for the contents of a selection, it specifies a selection target type. This target type can be used to control the transmitted representation of the contents. For example, if the selection is ``the last thing the user clicked on'' and that is currently an image, then the target type might specify whether the contents of the image should be sent in XY format or Z format. The target type can also be used to control the class of contents transmitted, for example, asking for the ``looks'' (fonts, line spacing, indentation, and so forth) of a paragraph selection, not the text of the paragraph. The target type can also be used for other purposes. The protocol does not constrain the semantics. To set the selection owner, use . Selectionsetting the owner XSetSelectionOwner XSetSelectionOwner Display *display Atom selection Window owner Time time display Specifies the connection to the X server. selection Specifies the selection atom. owner Specifies the owner of the specified selection atom. You can pass a window or None. time Specifies the time. You can pass either a timestamp or CurrentTime. The function changes the owner and last-change time for the specified selection and has no effect if the specified time is earlier than the current last-change time of the specified selection or is later than the current X server time. Otherwise, the last-change time is set to the specified time, with CurrentTime replaced by the current server time. If the owner window is specified as None, then the owner of the selection becomes None (that is, no owner). Otherwise, the owner of the selection becomes the client executing the request. If the new owner (whether a client or None) is not the same as the current owner of the selection and the current owner is not None, the current owner is sent a SelectionClear event. If the client that is the owner of a selection is later terminated (that is, its connection is closed) or if the owner window it has specified in the request is later destroyed, the owner of the selection automatically reverts to None, but the last-change time is not affected. The selection atom is uninterpreted by the X server. returns the owner window, which is reported in SelectionRequest and SelectionClear events. Selections are global to the X server. can generate BadAtom and BadWindow errors. To return the selection owner, use . Selectiongetting the owner XGetSelectionOwner Window XGetSelectionOwner Display *display Atom selection display Specifies the connection to the X server. selection Specifies the selection atom (Se. The function returns the window ID associated with the window that currently owns the specified selection. If no selection was specified, the function returns the constant None. If None is returned, there is no owner for the selection. can generate a BadAtom error. To request conversion of a selection, use . Selectionconverting XConvertSelection XConvertSelection Display *display Atomselection, target Atom property Window requestor Time time display Specifies the connection to the X server. selection Specifies the selection atom. target Specifies the target atom. property Specifies the property name. You also can pass None. requestor Specifies the requestor. time Specifies the time. You can pass either a timestamp or CurrentTime. requests that the specified selection be converted to the specified target type: If the specified selection has an owner, the X server sends a SelectionRequest event to that owner. If no owner for the specified selection exists, the X server generates a SelectionNotify event to the requestor with property None. The arguments are passed on unchanged in either of the events. There are two predefined selection atoms: PRIMARY and SECONDARY. can generate BadAtom and BadWindow errors.