XLoadFont(3X11)XLoadFont(3X11)NAME
XLoadFont, XQueryFont, XLoadQueryFont, XFreeFont, XGetFontProperty,
XUnloadFont, XCharStruct, XFontProp, XChar2b, XFontStruct - load or
unload fonts and font metric structures
SYNOPSIS
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
Specifies the atom for the property name you want returned. Specifies
the connection to the X server. Specifies the font. Specifies the
font ID or the GContext ID. Specifies the storage associated with the
font. Specifies the GC. Specifies the name of the font, which is a
null-terminated string. 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
using 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
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 proper‐
ties 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 addi‐
tional
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 base‐
line
for spacing */
int descent; /* logical decent below base‐
line
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 direc‐
tion 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 met‐
ric. The core protocol defines no support for vertical text. If the
min_byte1 and max_byte1 members are both zero, min_char_or_byte2 speci‐
fies the linear character index corresponding to the first element of
the per_char array, and max_char_or_byte2 specifies the linear charac‐
ter 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 unde‐
fined 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. 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 charac‐
ters). The bounding box of the font (the smallest rectangle
enclosing the shape obtained by superimposing all of the charac‐
ters 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 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
defines the extent of the top edge of the character ink from the ori‐
gin. 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
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 ALSOXCreateGC(3X11), XListFonts(3X11), XSetFontPath(3X11)
Xlib -- C Language X Interface
XLoadFont(3X11)
