mantic (3) XFreeFont.3.gz

Provided by: libx11-doc_1.8.6-1ubuntu1_all bug

NAME

       XLoadFont,   XQueryFont,   XLoadQueryFont,   XFreeFont,   XGetFontProperty,   XUnloadFont,
       XCharStruct, XFontProp, XChar2b, XFontStruct -  load  or  unload  fonts  and  font  metric
       structures

SYNTAX

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

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

       XFontStruct *XLoadQueryFont(Display *display, _Xconst 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 Conventions.
       If XLoadFont was unsuccessful at loading the specified  font,  a  BadName  error  results.
       Fonts  are not associated with a particular screen and can be stored as a component 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 function returns the value  of  the
       specified  font  property.   XGetFontProperty  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.

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
       characters: byte1 specifies the range of defined rows  and  byte2  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 characters.

       The bounding box of a character is defined by the XCharStruct  of  that  character.   When
       characters  are  absent  from  a  font,  the  default_char  is  used.  When fonts have all
       characters 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 character 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
            corresponding 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 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  +
            descent.

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

       [x + lbearing, y - ascent]

       Its width is:

       rbearing - lbearing

       Its height is:

       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
       character  ink  from  the  origin.   The  width  member  defines  the logical 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(3), XListFonts(3), XSetFontPath(3)
       Xlib - C Language X Interface