XLoadFont(3X11) XLIB FUNCTIONS XLoadFont(3X11)NAME
XLoadFont, XQueryFont, XLoadQueryFont, XFreeFont, XGet-
FontProperty, XUnloadFont, XCharStruct, XFontProp,
XChar2b, XFontStruct - load or unload fonts and font met-
ric 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 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.
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XLoadFont(3X11) XLIB FUNCTIONS XLoadFont(3X11)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 ``?'' charac-
ter will match any single character, and the ``*'' charac-
ter 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 associ-
ated 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 appropri-
ate XFontStruct structure. If the font name is not in the
Host Portable Character Encoding, the result is implemen-
tation-dependent. If the font does not exist, XLoadQuery-
Font 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 prede-
fined 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 guaran-
teed, it is likely that the predefined font properties
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XLoadFont(3X11) XLIB FUNCTIONS XLoadFont(3X11)
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 con-
tain:
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;
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XLoadFont(3X11) XLIB FUNCTIONS XLoadFont(3X11)
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 seman-
tics:
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
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 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.
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XLoadFont(3X11) XLIB FUNCTIONS XLoadFont(3X11)
o If all_chars_exist is True, 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 charac-
ter is printed. The default_char is a 16-bit charac-
ter (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 sig-
nificant 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 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
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-coordi-
nate 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
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XLoadFont(3X11) XLIB FUNCTIONS XLoadFont(3X11)
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 ALSOXCreateGC(3X11), XListFonts(3X11), XSetFontPath(3X11)
Xlib - C Language X Interface
X Version 11 Release 6.4 6
