XCURSOR(3)

NAME
Xcursor - Cursor management library

SYNOPSIS
#include <X11/Xcursor/Xcursor.h>

DESCRIPTION
Xcursor is a simple library designed to help locate and load cursors. Cursors can be loaded from files or memory. A library of common cursors exists which map to the standard X cursor names. Cursors can exist in several sizes and the library automatically picks the best size.

FUNCTIONAL OVERVIEW
Xcursor is built in a couple of layers; at the bottom layer is code which can load cursor images from files. Above that is a layer which locates cursor files based on the library path and theme. At the top is a layer which builds cursors either out of an image loaded from a file or one of the standard X cursors. When using images loaded from files, Xcursor prefers to use the Render extension CreateCursor request if supported by the X server. Where not supported, Xcursor maps the cursor image to a standard X cursor and uses the core CreateCursor request.

  CURSOR FILES
Xcursor defines a new format for cursors on disk. Each file holds one or more cursor images. Each cursor image is tagged with a nominal size so that the best size can be selected automatically. Multiple cursors of the same nominal size can be loaded together; applications are expected to use them as an animated sequence.

Cursor files are stored as a header containing a table of contents followed by a sequence of chunks. The table of contents indicates the type, subtype and position in the file of each chunk. The file header looks like:

magic:    CARD32 "Xcur" (0x58, 0x63, 0x75, 0x72)
header:    CARD32 bytes in this header
version:    CARD32 file version number
ntoc:    CARD32 number of toc entries
toc:    LISTofTOC table of contents

Each table of contents entry looks like:

type:    CARD32 entry type
subtype:    CARD32 type-specific label - size for images
position:    CARD32 absolute byte position of table in file

Each chunk in the file has set of common header fields followed by additional type-specific fields:

header:    CARD32 bytes in chunk header (including type-specific fields)
type:    CARD32 must match type in TOC for this chunk
subtype:    CARD32 must match subtype in TOC for this chunk
version:    CARD32 version number for this chunk type

There are currently two chunk types defined for cursor files; comments and images. Comments look like:

header:    20 Comment headers are 20 bytes
type:    0xfffe0001 Comment type is 0xfffe0001
subtype:    { 1 (COPYRIGHT), 2 (LICENSE), 3 (OTHER) }
version:    1
length:    CARD32 byte length of UTF-8 string
string:    LISTofCARD8 UTF-8 string

Images look like:

header:    36 Image headers are 36 bytes
type:    0xfffd0002 Image type is 0xfffd0002
subtype:    CARD32 Image subtype is the nominal size
version:    1
width:    CARD32 Must be less than or equal to 0x7fff
height:    CARD32 Must be less than or equal to 0x7fff
xhot:    CARD32 Must be less than or equal to width
yhot:    CARD32 Must be less than or equal to height
delay:    CARD32 Delay between animation frames in milliseconds
pixels:    LISTofCARD32 Packed ARGB format pixels

  THEMES
Xcursor (mostly) follows the freedesktop.org spec for theming icons. The default search path it uses is

    ~/.icons, /usr/local/lib/X11/icons, /usr/local/share/icons, /usr/local/share/pixmaps, /usr/X11R6/share/icons, /usr/X11R6/share/pixmaps

Within each of these directories, it searches for a directory using the theme name: Within the theme directory, it looks for cursor files in the “cursors” subdirectory.

    Xcursor looks for a specific file, which must be one of the cursor shape names, e.g., as used in XcursorLibraryLoadImage or XcursorLibraryShape. If it finds no matching cursor file in the “cursors” subdirectory, Xcursor next looks for an “index.theme” file in each theme directory to look for inherited themes. Those are lines in this format:

    Inherits = theme-name

    Xcursor uses the first inherited theme-name, ignoring others which may exist in a given “index.theme” file. If it finds an inherited theme, Xcursor searches along the path to use that as well. Xcursor ignores other keys in the “index.theme” file, including “Name” (i.e., the name which a graphical application may use as the presentation name).

    More than one theme-name may be listed on the Inherits= line. The freedesktop.org spec states that list items are separated by commas. Xcursor also accepts semicolon, but translates both to colon when searching the path. Xcursor expects only one Inherits= line; the freedesktop.org spec is unclear whether multiple keys are allowed.

If no theme is set, or if no cursor is found for the specified theme anywhere along the path, Xcursor checks the “default” theme.

When Xcursor finds a cursor file, it stops searching. It always uses the first cursor file found while searching along the path.

DATATYPES

XcursorImage
    holds a single cursor image in memory. Each pixel in the cursor is a 32-bit value containing ARGB with A in the high byte.

    typedef struct _XcursorImage {
        XcursorDim      size;     /* nominal size for matching */
        XcursorDim      width;     /* actual width */
        XcursorDim      height;     /* actual height */
        XcursorDim      xhot;     /* hot spot x (must be inside image) */
        XcursorDim      yhot;     /* hot spot y (must be inside image) */
        XcursorPixel     *pixels;     /* pointer to pixels */
    } XcursorImage;

XcursorImages
    holds multiple XcursorImage structures. They are all freed when the XcursorImages is freed in XcursorImagesDestroy.

    typedef struct _XcursorImages {
        int      nimage;     /* number of images */
        XcursorImage     **images;     /* array of XcursorImage pointers */
    } XcursorImages;

XcursorCursors
    Holds multiple Cursor objects. They are all freed when the XcursorCursors is freed. These are reference counted so that multiple XcursorAnimate structures can use the same XcursorCursors.

    typedef struct _XcursorCursors {
        Display     *dpy;     /* Display holding cursors */
        int      ref;     /* reference count */
        int      ncursor;     /* number of cursors */
        Cursor     *cursors;     /* array of cursors */
    } XcursorCursors;

XcursorAnimate
    References a set of cursors and a sequence within that set. Multiple XcursorAnimate structures may reference the same XcursorCursors; each holds a reference which is removed when the XcursorAnimate is freed.

    typedef struct _XcursorAnimate {
        XcursorCursors     *cursors;     /* list of cursors to use */
        int      sequence;     /* which cursor is next */
    } XcursorAnimate;

XcursorFile
    Xcursor provides an abstract API for accessing the file data. Xcursor provides a stdio implementation of this abstract API; applications are free to create additional implementations. These functions parallel the stdio functions in return value and expected argument values; the read and write functions flip the arguments around to match the POSIX versions.

    typedef struct _XcursorFile {
        void *closure;
        int (*read) (XcursorFile *file, unsigned char *buf, int len);
        int (*write) (XcursorFile *file, unsigned char *buf, int len);
        int (*seek) (XcursorFile *file, long offset, int whence); };

FUNCTIONS

  Object Management
Allocate and free images. On allocation, the hotspot and the pixels are left uninitialized. The size is set to the maximum of width and height. Allocate and free arrays to hold multiple cursor images. On allocation, nimage is set to zero. Allocate and free arrays to hold multiple cursors. On allocation, ncursor is set to zero, ref is set to one.

  Reading and writing images.
These read and write cursors from an XcursorFile handle. After reading, the file pointer will be left at some random place in the file. These read and write cursors from a stdio FILE handle. Writing flushes before returning so that any errors should be detected. These parallel the stdio FILE interfaces above, but take filenames.

  Reading library images
These search the library path, loading the first file found of the desired size, using a private function (XcursorScanTheme) to find the appropriate theme:
    If theme is not NULL, use that. If theme is NULL, or if there was no match for the desired theme, use “default” for the theme name. If neither search succeeds, these functions return NULL.

    The two functions differ by more than the number of images loaded:
    XcursorLibraryLoadImage calls XcursorFileLoadImage but XcursorLibraryLoadImages calls XcursorFileLoadImages, and (on success) it calls XcursorImagesSetName to associate name with the result.

  Library attributes
Returns the library search path:
    If the environment variable XCURSOR_PATH is set, return that value. Otherwise, return the compiled-in search path.
Search Xcursor's table of cursor font names for the given “shape name” (library):
    If found, return the index into that table, multiplied by two (to account for the source- and mask-values used in an X cursor font). If not found, return -1.

  Cursor APIs
These load cursors from the specified file. These load cursors using the specified library name. The theme comes from the display. This creates a cursor, given the image to display. It calls XcursorSupportsARGB to decide what type of cursor to create:
    XRenderCreateCursor is used if ARGB is supported on the display, and XCreatePixmapCursor is used otherwise.
This provides an interface for creating animated cursors, if the images array contains multiple images, and if XcursorSupportsAnim returns true. Otherwise, it calls XcursorImageLoadCursor. This calls XcursorCursorsCreate to create an array of XcursorCursors, to correspond to the XcursorImages images array, and uses XcursorImageLoadCursor to load the corresponding cursor data.

    Normally it returns the resulting array pointer. On any failure, it discards the result XcursorCursorsDestroy, and returns NULL.

  X Cursor Name APIs
These map shape to a library name using the standard X cursor names and then load the images. These map shape to a library name and then load the cursors.

  X Cursor Comment APIs
XcursorXcFileLoad uses this function to allocate an XcursorComment structure for a single cursor. The comment_type parameter is used as the subtype field, e.g., COPYRIGHT. The length is the number of bytes to allocate for the comment text. Deallocates the given XcursorComment structure. XcursorXcFileLoad uses this function to allocate an index of XcursorComment structure pointers. The size parameter tells it how many pointers will be in the index. Deallocates the given XcursorComments structure as well as the XcursorComment structures which it points to.

  Animated Cursors
Wrap the given array of cursors in a newly allocated XcursorAnimate structure, which adds a sequence number used in XcursorAnimateNext. Discards the given animate data, freeing both the XcursorCursors array of cursors as well as the XcursorAnimate structure. Cyclically returns the next Cursor in the array, incrementing the sequence number to prepare for the next call.

    The caller is responsible for displaying the series of Cursor images. Xcursor does not do that.

  Glyph Cursor APIs
The X11 XCreateFontCursor and XCreateGlyphCursor functions use this part of the API to extend the X core cursors feature to use themes. Compute a hash of the image, to display when the environment variable XCURSOR_DISCOVER is set. Associates the given name with the images. Check if the display supports either ARGB or themes, and also if the image size fits within the maximum cursor size (64 pixels). If so, create a bitmap of the specified size, and cache the result in Xcursor, identifying it with the Pixmap-id (pid) value. Update the image contents in the bitmap specified by the draw value (a Pixmap-id). The bitmap must have been created by XcursorNoticeCreateBitmap. If the display supports either ARGB or themes, try to load a cursor into Xcursor's cache using the source parameter as a Pixmap-id. The source may no longer be in the cache. Xcursor uses the hash value to identify the desired image. If the display supports either ARGB or themes, try to load a cursor into Xcursor's cache using the source_char parameter as a shape. Using
    the default size from XcursorGetDefaultSize, the default theme from XcursorGetTheme, and the source_char parameter as a shape,

    Xcursor calls XcursorShapeLoadImages to load the cursor images. If successful, Xcursor uses XcursorImagesLoadCursor to load the cursor information.

  Display Information APIs
Returns true if the display supports ARGB cursors. Otherwise, cursors will be mapped to a core X cursor. Returns true if the display supports animated cursors. Otherwise, cursors will be mapped to a core X cursor. Sets the default size for cursors on the specified display. When loading cursors, those whose nominal size is closest to this size will be preferred. Gets the default cursor size. Sets the current theme name. Gets the current theme name. Get or set property which tells Xcursor whether to enable themes for core cursors.

ENVIRONMENT VARIABLES
Environment variables can be used to override resource settings, which in turn override compiled-in default values.

Some of the environment variables recognized by Xcursor are booleans, specified as follows:

    true for “t”, “1”, “y” or “on”

    false for “f”, “0”, “n” or “off”

Xcursor ignores other values for these booleans.

HOME
    Xcursor interprets “~” in the search list as the home directory, using this variable rather than the password database.

XCURSOR_ANIM
    If the display supports the Render CreateCursor request, and the Render feature is enabled, disable animated cursors if the environment variable is false.

    If the environment variable is not given, Xcursor uses the resource Xcursor.anim.

XCURSOR_CORE
    If the display supports the Render CreateCursor request disable the Render feature if the environment variable is false.

    If the environment variable is not given, Xcursor uses the resource Xcursor.core.

XCURSOR_DISCOVER
    If the variable is set, Xcursor turns on a logging feature. It displays the hash value and the image so that users can see which cursor name is associated with each image.

    There is no corresponding resource setting.

XCURSOR_DITHER
    This variable sets the desired dither.

    If the environment variable is not given, Xcursor uses the resource Xcursor.dither.

    If neither environment variable or resource is found, Xcursor uses “threshold”

    These are the recognized values:

    diffuse

    median

    ordered

    threshold

XCURSOR_PATH
    This variable sets the list of paths in which to search for cursors, rather than the compiled-in default list.

    Directories in this path are separated by colons (:).

XCURSOR_SIZE
    This variable sets the desired cursor size, in pixels.

    If the environment variable is not given, Xcursor tries the Xcursor.size resource.

    If no size is given, whether by environment variable or resource setting, Xcursor next tries the Xft.dpi resource setting to guess the size of a 16-point cursor.

    Finally, if Xft.dpi is not set, Xcursor uses the display height, dividing by 48 (assuming that the height is 768).

XCURSOR_THEME
    This variable selects the desired theme.

    If the environment variable is not given, Xcursor tries the Xcursor.theme resource.

    If neither environment variable or resource is found, Xcursor uses the default theme.

XCURSOR_THEME_CORE
    Enables themes for core cursors if the environment variable is true.

    If the environment variable is not given, Xcursor tries the Xcursor.theme_core resource.

    An application can enable or disable themes using XcursorSetThemeCore.

SEE ALSO
XCreateRenderCursor(3), XCreatePixmapCursor(3), and XCreateFontCursor(3)

as well as

    Icon Theme Specification
    https://specifications.freedesktop.org/icon-theme-spec/

RESTRICTIONS
Xcursor will probably change radically in the future; weak attempts will be made to retain some level of source-file compatibility.

AUTHOR
Keith Packard