XLoadFont(3X11) MIT X11R4 XLoadFont(3X11)
Name
XLoadFont, XQueryFont, XLoadQueryFont, XFreeFont, XGetFontProperty, XUnloadFont, XCharStruct, XFontProp, XChar2b, XFontStruct - load or
unload fonts and font metric structures
Syntax
Font XLoadFont(display, name)
Display *display;
char *name;
XFontStruct *XQueryFont(display, font_ID)
Display *display;
XID font_ID;
XFontStruct *XLoadQueryFont(display, name)
Display *display;
char *name;
XFreeFont(display, font_struct)
Display *display;
XFontStruct *font_struct;
Bool XGetFontProperty(font_struct, atom, value_return)
XFontStruct *font_struct;
Atom atom;
unsigned long *value_return;
XUnloadFont(display, font)
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 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 function loads the specified font and returns its associated font ID. The name should be ISO Latin-1 encoding; uppercase and lowercase
do not matter. The interpretation of characters ``?'' (octal value 77) and ``*'' (octal value 52) in the name is not defined by the core
protocol but is reserved for future definition. A structured format for font names is specified in the X Consortium standard X Logical
Font Description Conventions. If was unsuccessful at loading the specified font, a error results. Fonts are not associated with a partic-
ular screen and can be stored as a component of any GC. When the font is no longer needed, call
can generate and errors.
The function returns a pointer to the 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 structure will be the ID, and you need to be careful when using this ID in other functions (see
To free this data, use
can generate a error.
The function provides the most common way for accessing a font. both opens (loads) the specified font and returns a pointer to the appro-
priate structure. If the font does not exist, returns NULL.
The function deletes the association between the font resource ID and the specified font and frees the structure. The font itself will be
freed when no other resource references it. The data and the font should not be referenced again.
can generate a error.
Given the atom for that property, the function returns the value of the specified font property. also returns if the property was not
defined or if it was defined. A set of predefined atoms exists for font properties, which can be found in 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 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.
can generate a error.
Structures
The 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 structures for the characters contained in the font. The and 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; /* baselink 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 char 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 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 min and max bounds are used.
The members of the have the following semantics:
o The direction member can be either or It is just a hint as to whether most elements have a positive or a negative character width met-
ric. The core protocol defines no support 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 corresponding to the per_char array element N (counting from 0) are:
byte1 = N/D + min_byte1
byte2 = ND + 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 all characters in the per_char array have nonzero bounding 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 char-
acter, 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 individual 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 superimpos-
ing 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). 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 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 logi-
cal width of the character.
Diagnostics
The server failed to allocate the requested resource or server memory.
A value for a Font or GContext argument does not name a defined Font.
A font or color of the specified name does not exist.
See Also
XCreateGC(3X11), XListFonts(3X11), XSetFontPath(3X11)
X Window System: The Complete Reference, Second Edition, Robert W. Scheifler and James Gettys
XLoadFont(3X11)