XLoadFont(3X11) X11 SDE 5.4R3.00 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, fontID)
Display *display;
XID fontID;
XFontStruct *XLoadQueryFont(display, name)
Display *display;
char *name;
XFreeFont(display, fontstruct)
Display *display;
XFontStruct *fontstruct;
Bool XGetFontProperty(fontstruct, atom, valuereturn)
XFontStruct *fontstruct;
Atom atom;
unsigned long *valuereturn;
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.
fontID Specifies the font ID or the GContext ID.
fontstruct
Specifies the storage associated with the font.
gc Specifies the GC.
name Specifies the name of the font, which is a null-terminated
string.
valuereturn
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
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Character Encoding the result is implementation dependent. Use of
uppercase or lowercase does not matter. The interpretation of
characters ``?'' and ``*'' 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 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
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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
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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]
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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.
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BadName A font or color of the specified name does not exist.
SEE ALSO
XCreateGC(3X11), XListFonts(3X11), XSetFontPath(3X11)
Xlib - C Language X Interface
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