NAME
XLoadFont, XQueryFont, XLoadQueryFont, XFreeFont, XGetFontProperty, XUnloadFont,
XCharStruct, XFontProp, XChar2b, XFontStruct - load or unload fonts and font
metric structures
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 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 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
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 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.
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 properties
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 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
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 semantics:
- •
- 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.
- •
- 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 = 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
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.
- •
- 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
- •
- 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 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 ALSO
XCreateGC(3), XListFonts(3), XSetFontPath(3)
Xlib - C Language X Interface