MirOS Manual: XChar2b(3), XCharStruct(3), XFontProp(3), XFontStruct(3), XFreeFont(3), XGetFontProperty(3), XLoadFont(3), XLoadQueryFont(3), XQueryFont(3), XUnloadFont(3)


XLoadFont(3X11)          XLIB FUNCTIONS           XLoadFont(3X11)

NAME

     XLoadFont, XQueryFont, XLoadQueryFont, XFreeFont, XGet-
     FontProperty, XUnloadFont, XCharStruct, XFontProp, XChar2b,
     XFontStruct - load or unload fonts and font metric struc-
     tures

SYNTAX

     Font XLoadFont(Display *display, char *name);

     XFontStruct *XQueryFont(Display *display, XID font_ID);

     XFontStruct *XLoadQueryFont(Display *display, char *name);

     int XFreeFont(Display *display, XFontStruct *font_struct);

     Bool XGetFontProperty(XFontStruct *font_struct, Atom atom,
          unsigned long *value_return);

     int XUnloadFont(Display *display, Font font);

ARGUMENTS

     atom      Specifies the atom for the property name you want
               returned.

     display   Specifies the connection to the X server.

     font      Specifies the font.

     font_ID   Specifies the font ID or the GContext ID.

     font_struct
               Specifies the storage associated with the font.

     gc        Specifies the GC.

     name      Specifies the name of the font, which is a null-
               terminated string.

     value_return
               Returns the value of the font property.

DESCRIPTION

     The XLoadFont function loads the specified font and returns
     its associated font ID. If the font name is not in the Host
     Portable Character Encoding, the result is implementation-
     dependent. Use of uppercase or lowercase does not matter.
     When the characters ``?'' and ``*'' are used in a font name,
     a pattern match is performed and any matching font is used.
     In the pattern, the ``?'' character will match any single
     character, and the ``*'' character will match any number of
     characters. A structured format for font names is specified
     in the X Consortium standard X Logical Font Description

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XLoadFont(3X11)          XLIB FUNCTIONS           XLoadFont(3X11)

     Conventions. If XLoadFont was unsuccessful at loading the
     specified font, a BadName error results. Fonts are not asso-
     ciated with a particular screen and can be stored as a com-
     ponent of any GC. When the font is no longer needed, call
     XUnloadFont.

     XLoadFont can generate BadAlloc and BadName errors.

     The XQueryFont function returns a pointer to the XFontStruct
     structure, which contains information associated with the
     font. You can query a font or the font stored in a GC. The
     font ID stored in the XFontStruct structure will be the
     GContext ID, and you need to be careful when using this ID
     in other functions (see XGContextFromGC). If the font does
     not exist, XQueryFont returns NULL. To free this data, use
     XFreeFontInfo.

     XLoadQueryFont can generate a BadAlloc error.

     The XLoadQueryFont function provides the most common way for
     accessing a font. XLoadQueryFont both opens (loads) the
     specified font and returns a pointer to the appropriate
     XFontStruct structure. If the font name is not in the Host
     Portable Character Encoding, the result is implementation-
     dependent. If the font does not exist, XLoadQueryFont
     returns NULL.

     The XFreeFont function deletes the association between the
     font resource ID and the specified font and frees the
     XFontStruct structure. The font itself will be freed when no
     other resource references it. The data and the font should
     not be referenced again.

     XFreeFont can generate a BadFont error.

     Given the atom for that property, the XGetFontProperty func-
     tion returns the value of the specified font property. XGet-
     FontProperty also returns False if the property was not
     defined or True if it was defined. A set of predefined atoms
     exists for font properties, which can be found in
     <X11/Xatom.h>. This set contains the standard properties
     associated with a font. Although it is not guaranteed, it is
     likely that the predefined font properties will be present.

     The XUnloadFont function deletes the association between the
     font resource ID and the specified font. The font itself
     will be freed when no other resource references it. The font
     should not be referenced again.

     XUnloadFont can generate a BadFont error.

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XLoadFont(3X11)          XLIB FUNCTIONS           XLoadFont(3X11)

STRUCTURES

     The XFontStruct structure contains all of the information
     for the font and consists of the font-specific information
     as well as a pointer to an array of XCharStruct structures
     for the characters contained in the font. The XFontStruct,
     XFontProp, and XCharStruct structures contain:

     typedef struct {
          short lbearing;          /* origin to left edge of raster */
          short rbearing;          /* origin to right edge of raster */
          short width;             /* advance to next char's origin */
          short ascent;            /* baseline to top edge of raster */
          short descent;           /* baseline to bottom edge of raster */
          unsigned short attributes;/* per char flags (not predefined) */
     } XCharStruct;

     typedef struct {
          Atom name;
          unsigned long card32;
     } XFontProp;

     typedef struct {              /* normal 16 bit characters are two bytes */
         unsigned char byte1;
         unsigned char byte2;
     } XChar2b;

     typedef struct {
          XExtData *ext_data;      /* hook for extension to hang data */
          Font fid;                /* Font id for this font */
          unsigned direction;      /* hint about the direction font is painted */
          unsigned min_char_or_byte2;/* first character */
          unsigned max_char_or_byte2;/* last character */
          unsigned min_byte1;      /* first row that exists */
          unsigned max_byte1;      /* last row that exists */
          Bool all_chars_exist;    /* flag if all characters have nonzero size */
          unsigned default_char;   /* char to print for undefined character */
          int n_properties;        /* how many properties there are */
          XFontProp *properties;   /* pointer to array of additional properties */
          XCharStruct min_bounds;  /* minimum bounds over all existing char */
          XCharStruct max_bounds;  /* maximum bounds over all existing char */
          XCharStruct *per_char;   /* first_char to last_char information */
          int ascent;              /* logical extent above baseline for spacing */
          int descent;             /* logical decent below baseline for spacing */
     } XFontStruct;

     X supports single byte/character, two bytes/character
     matrix, and 16-bit character text operations. Note that any
     of these forms can be used with a font, but a single
     byte/character text request can only specify a single byte
     (that is, the first row of a 2-byte font). You should view
     2-byte fonts as a two-dimensional matrix of defined charac-
     ters: byte1 specifies the range of defined rows and byte2

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XLoadFont(3X11)          XLIB FUNCTIONS           XLoadFont(3X11)

     defines the range of defined columns of the font. Single
     byte/character fonts have one row defined, and the byte2
     range specified in the structure defines a range of charac-
     ters.

     The bounding box of a character is defined by the XChar-
     Struct of that character. When characters are absent from a
     font, the default_char is used. When fonts have all charac-
     ters of the same size, only the information in the
     XFontStruct min and max bounds are used.

     The members of the XFontStruct have the following semantics:

     +    The direction member can be either FontLeftToRight or
          FontRightToLeft. It is just a hint as to whether most
          XCharStruct elements have a positive (FontLeftToRight)
          or a negative (FontRightToLeft) character width metric.
          The core protocol defines no support for vertical text.

     +    If the min_byte1 and max_byte1 members are both zero,
          min_char_or_byte2 specifies the linear character index
          corresponding to the first element of the per_char
          array, and max_char_or_byte2 specifies the linear char-
          acter index of the last element.

          If either min_byte1 or max_byte1 are nonzero, both
          min_char_or_byte2 and max_char_or_byte2 are less than
          256, and the 2-byte character index values correspond-
          ing to the per_char array element N (counting from 0)
          are:

               byte1 = N/D + min_byte1
               byte2 = N\D + min_char_or_byte2

          where:

                  D = max_char_or_byte2 - min_char_or_byte2 + 1
                  / = integer division
                  \ = integer modulus

     +    If the per_char pointer is NULL, all glyphs between the
          first and last character indexes inclusive have the
          same information, as given by both min_bounds and
          max_bounds.

     +    If all_chars_exist is True, all characters in the
          per_char array have nonzero bounding boxes.

     +    The default_char member specifies the character that

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XLoadFont(3X11)          XLIB FUNCTIONS           XLoadFont(3X11)

          will be used when an undefined or nonexistent character
          is printed. The default_char is a 16-bit character (not
          a 2-byte character). For a font using 2-byte matrix
          format, the default_char has byte1 in the most-
          significant byte and byte2 in the least significant
          byte. If the default_char itself specifies an undefined
          or nonexistent character, no printing is performed for
          an undefined or nonexistent character.

     +    The min_bounds and max_bounds members contain the most
          extreme values of each individual XCharStruct component
          over all elements of this array (and ignore nonexistent
          characters). The bounding box of the font (the smallest
          rectangle enclosing the shape obtained by superimposing
          all of the characters at the same origin [x,y]) has its
          upper-left coordinate at:
               [x + min_bounds.lbearing, y - max_bounds.ascent]

          Its width is:
               max_bounds.rbearing - min_bounds.lbearing

          Its height is:
               max_bounds.ascent + max_bounds.descent

     +    The ascent member is the logical extent of the font
          above the baseline that is used for determining line
          spacing. Specific characters may extend beyond this.

     +    The descent member is the logical extent of the font at
          or below the baseline that is used for determining line
          spacing. Specific characters may extend beyond this.

     +    If the baseline is at Y-coordinate y, the logical
          extent of the font is inclusive between the Y-
          coordinate values (y - font.ascent) and (y +
          font.descent - 1). Typically, the minimum interline
          spacing between rows of text is given by ascent + des-
          cent.

     For a character origin at [x,y], the bounding box of a char-
     acter (that is, the smallest rectangle that encloses the
     character's shape) described in terms of XCharStruct com-
     ponents is a rectangle with its upper-left corner at:

     [x + lbearing, y - ascent]

     Its width is:

     rbearing - lbearing

     Its height is:

XFree86                   Version 4.5.0                         5

XLoadFont(3X11)          XLIB FUNCTIONS           XLoadFont(3X11)

     ascent + descent

     The origin for the next character is defined to be:

     [x + width, y]

     The lbearing member defines the extent of the left edge of
     the character ink from the origin. The rbearing member
     defines the extent of the right edge of the character ink
     from the origin. The ascent member defines the extent of the
     top edge of the character ink from the origin. The descent
     member defines the extent of the bottom edge of the charac-
     ter ink from the origin. The width member defines the logi-
     cal width of the character.

DIAGNOSTICS

     BadAlloc  The server failed to allocate the requested
               resource or server memory.

     BadFont   A value for a Font or GContext argument does not
               name a defined Font.

     BadName   A font or color of the specified name does not
               exist.

SEE ALSO

     XCreateGC(3X11), XListFonts(3X11), XSetFontPath(3X11)
     Xlib - C Language X Interface

XFree86                   Version 4.5.0                         6

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