XLoadFont(3X11) RISC/os Reference Manual XLoadFont(3X11)
NAME
XLoadFont, XQueryFont, XLoadQueryFont, XFreeFont, XGet-
FontProperty, XUnloadFont, XCharStruct, XFontProp, XChar2b,
XFontStruct - load or unload fonts and font metric struc-
tures
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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DESCRIPTION
The XLoadFont function loads the specified font and returns
its associated font ID. The name should be ISO Latin-1
encoding; uppercase and lowercase do not matter. The
interpretation of characters ``?'' (octal value 77) and
``*'' (octal value 52) 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 Con-
sortium 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 par-
ticular 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). 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 does not exist, XLoad-
QueryFont 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 func-
tion returns the value of the specified font property. XGet-
FontProperty 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
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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
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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 charac-
ters.
The bounding box of a character is defined by the XChar-
Struct of that character. When characters are absent from a
font, the default_char is used. When fonts have all charac-
ters 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 char-
acter 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 correspond-
ing 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.
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⊕ 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 unde-
fined or nonexistent character, no printing is per-
formed 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 smal-
lest rectangle enclosing the shape obtained by superim-
posing 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 + des-
cent.
For a character origin at [x,y], the bounding box of a char-
acter (that is, the smallest rectangle that encloses the
character's shape) described in terms of XCharStruct com-
ponents is a rectangle with its upper-left corner at:
[x + lbearing, y - ascent]
Its width is:
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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 des-
cent 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(3X11), XListFonts(3X11), XSetFontPath(3X11)
Xlib - C Language X Interface
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