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X11R7.4 - man page for xchar2b (x11r4 section 3)

XLoadFont(3)				  XLIB FUNCTIONS			     XLoadFont(3)

NAME
       XLoadFont, XQueryFont, XLoadQueryFont, XFreeFont, XGetFontProperty, 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 implementa-
       tion-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 XLoad-
       Font 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.  XLoad-
       QueryFont 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 speci-
       fied 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 proper-
       ties 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 struc-
       tures 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/char-
       acter 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 speci-
       fied 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 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:

       o    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 sup-
	    port for vertical text.

       o    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 corre-
	    sponding 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

       o    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.

       o    If all_chars_exist is True, all characters in the per_char array have nonzero bound-
	    ing boxes.

       o    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.

       o    The min_bounds and max_bounds members contain the most extreme values of each indi-
	    vidual 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

       o    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.

       o    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.

       o    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).  Typi-
	    cally, 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 compo-
       nents 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 ori-
       gin.  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 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(3X11), XListFonts(3X11), XSetFontPath(3X11)
       Xlib - C Language X Interface

X Version 11				   libX11 1.2.1 			     XLoadFont(3)


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