XLoadFont(3) XLIB FUNCTIONS XLoadFont(3)
NAME
XLoadFont, XQueryFont, XLoadQueryFont, XFreeFont, XGetFontProperty,
XUnloadFont, XCharStruct, XFontProp, XChar2b, XFontStruct - load or un-
load 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 associ-
ated 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 charac-
ter, and the “*” character will match any number of characters. A
structured format for font names is specified in the X Consortium stan-
dard X Logical Font Description Conventions. If XLoadFont was unsuc-
cessful at loading the specified font, a BadName error results. Fonts
are not associated 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 us-
ing this ID in other functions (see XGContextFromGC). If the font does
not exist, XQueryFont returns NULL. To free this data, use XFree-
FontInfo.
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 re-
turns a pointer to the appropriate XFontStruct structure. If the font
name is not in the Host Portable Character Encoding, the result is im-
plementation-dependent. If the font does not exist, XLoadQueryFont re-
turns NULL.
The XFreeFont function deletes the association between the font re-
source 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 re-
turns 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 asso-
ciated 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 re-
source 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 charac-
ters: 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 infor-
mation 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 FontRight-
ToLeft. 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 correspond-
ing 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 de-
fault_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 nonexis-
tent 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 ob-
tained 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.as-
cent) and (y + font.descent - 1). Typically, the minimum inter-
line 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) de-
scribed in terms of XCharStruct components is a rectangle with its up-
per-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 charac-
ter ink from the origin. The rbearing member defines the extent of the
right edge of the character ink from the origin. The ascent member de-
fines 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 de-
fined 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
X Version 11 libX11 1.8.4 XLoadFont(3)
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