Description
The GdkFont data type represents a font for drawing on
the screen. These functions provide support for
loading fonts, and also for determining the dimensions
of characters and strings when drawn with a particular
font.
Fonts in X are specified by a
X Logical Font Description.
The following description is considerably simplified.
For definitive information about XLFD's see the
X reference documentation. A X Logical Font Description (XLFD)
consists of a sequence of fields separated (and surrounded by) '-'
characters. For example, Adobe Helvetica Bold 12 pt, has the
full description:
"-adobe-helvetica-bold-r-normal--12-120-75-75-p-70-iso8859-1" |
The fields in the XLFD are:
When specifying a font via a X logical Font Description,
'*' can be used as a wildcard to match any portion of
the XLFD. For instance, the above example could
also be specified as
"-*-helvetica-bold-r-normal--*-120-*-*-*-*-iso8859-1" |
It is generally a good idea to use wildcards for any
portion of the XLFD that your program does not care
about specifically, since that will improve the
chances of finding a matching font.
A fontset is a list of fonts
that is used for drawing international text that may
contain characters from a number of different character
sets. It is represented by a list of XLFD's.
The font for a given character set is determined by going
through the list of XLFD's in order. For each one, if
the registry and and encoding fields match the desired
character set, then that font is used, otherwise if
the XLFD contains wild-cards for the registry and encoding
fields, the registry and encoding for the desired character
set are subsituted in and a lookup is done. If a match is found
that font is used. Otherwise, processing continues
on to the next font in the list.
The functions for determining the metrics of a string
come in several varieties that can take a number
of forms of string input:
- 8-bit string
When using functions like gdk_string_width() that
take a gchar *, if the font is of type
GDK_FONT_FONT and is an 8-bit font, then each
gchar indexes the glyphs in the font directly.
- 16-bit string
For functions taking a gchar *, if the
font is of type GDK_FONT_FONT, and is a 16-bit
font, then the gchar * argument is
interpreted as a guint16 * cast to
a gchar * and each guint16
indexes the glyphs in the font directly.
- Multibyte string
For functions taking a gchar *, if the
font is of type GDK_FONT_FONTSET, then the input
string is interpreted as a multibyte
encoded according to the current locale. (A multibyte
string is one in which each character may consist
of one or more bytes, with different lengths for different
characters in the string). They can be converted to and
from wide character strings (see below) using
gdk_wcstombs() and gdk_mbstowcs().) The string will
be rendered using one or more different fonts from
the fontset.
- Wide character string
For a number of the text-measuring functions, GTK+
provides a variant (such as gdk_text_width_wc()) which
takes a GdkWChar * instead of a
gchar *. The input is then taken to
be a wide character string in the encoding of the
current locale. (A wide character string is a string
in which each character consists of several bytes,
and the width of each character in the string is
constant.)
GDK provides functions to determine a number of different
measurements (metrics) for a given string. (Need diagram
here).
- ascent
The vertical distance from the origin of the drawing
opereration to the top of the drawn character.
- descent
The vertical distance from the origin of the drawing
opereration to the bottom of the drawn character.
- left bearing
The horizontal distance from the origin of the drawing
operation to the left-most part of the drawn character.
- right bearing
The horizontal distance from the origin of the drawing
operation to the right-most part of the drawn character.
- width bearing
The horizontal distance from the origin of the drawing
operation to the correct origin for drawing another
string to follow the current one. Depending on the
font, this could be greater than or less than the
right bearing.
Details
struct GdkFont
struct GdkFont
{
GdkFontType type;
gint ascent;
gint descent;
}; |
The GdkFont structure represents a font or fontset. It
contains the following public fields. A new GdkFont
structure is returned by gdk_font_load() or gdk_fontset_load(),
and is reference counted with gdk_font_ref() and gdk_font_unref()
enum GdkFontType
typedef enum
{
GDK_FONT_FONT,
GDK_FONT_FONTSET
} GdkFontType; |
Indicates the type of a font. The possible values
are currently:
gdk_font_load ()
Loads a font.
Currently, this function will always return a new
font, however, in the future, it may be changed to
look up the font in a cache. You should make no
assumptions about the initial reference count.
gdk_fontset_load ()
Loads a fontset.
Currently this function will always return a new
font, however, in the future, it may be changed to
look up the font in a cache. You should make no
assumptions about the initial reference count.
gdk_font_ref ()
Increase the reference count of a count by one.
gdk_font_unref ()
void gdk_font_unref (GdkFont *font); |
Decrease the reference count of a count by one.
If the result is zero, destroys the font.
gdk_font_id ()
Returns the X Font ID for the given font.
gdk_font_equal ()
Compares two fonts for equality. Single fonts compare equal
if they have the same X font ID. This operation does
not currently work correctly for fontsets.
gdk_string_extents ()
Returns the metrics of a NULL-terminated string.
gdk_text_extents ()
Returns the metrics of a string.
gdk_text_extents_wc ()
Returns the metrics of a string of wide characters.
gdk_string_width ()
Determine the width of a NULL-terminated string.
(The distance from the origin of the string to the
point where the next string in a sequence of strings
should be drawn)
gdk_text_width ()
Determine the width of a given string.
gdk_text_width_wc ()
Determine the width of a given wide-character string.
gdk_char_width ()
Determine the width of a given character.
gdk_char_width_wc ()
Determine the width of a given wide character. (Encoded
in the wide-character encoding of the current locale).
gdk_string_measure ()
Determines the distance from the origin to the rightmost
portion of a NULL-terminated string when drawn. This is not the
correct value for determining the origin of the next
portion when drawing text in multiple pieces.
See gdk_string_width().
gdk_text_measure ()
Determines the distance from the origin to the rightmost
portion of a string when drawn. This is not the
correct value for determining the origin of the next
portion when drawing text in multiple pieces.
See gdk_text_width().
gdk_char_measure ()
Determines the distance from the origin to the rightmost
portion of a character when drawn. This is not the
correct value for determining the origin of the next
portion when drawing text in multiple pieces.
gdk_string_height ()
Determines the total height of a given NULL-terminated
string. This value is not generally useful, because you
cannot determine how this total height will be drawn in
relation to the baseline. See gdk_string_extents().
gdk_text_height ()
Determines the total height of a given string.
This value is not generally useful, because you cannot
determine how this total height will be drawn in
relation to the baseline. See gdk_text_extents().
gdk_char_height ()
Determines the total height of a given character.
This value is not generally useful, because you cannot
determine how this total height will be drawn in
relation to the baseline. See gdk_text_extents().
GdkWChar
typedef guint32 GdkWChar; |
Specifies a wide character type, used to represent character codes.
This is needed since some native languages have character sets which have
more than 256 characters (Japanese and Chinese, for example).
Wide character values between 0 and 127 are always identical in meaning to
the ASCII character codes. The wide character value 0 is often used to
terminate strings of wide characters in a similar way to normal strings
using the char type.
An alternative to wide characters is multi-byte characters, which extend
normal char strings to cope with larger character sets. As the name suggests,
multi-byte characters use a different number of bytes to store different
character codes. For example codes 0-127 (i.e. the ASCII codes) often
use just one byte of memory, while other codes may use 2, 3 or even 4 bytes.
Multi-byte characters have the advantage that they can often be used in an
application with little change, since strings are still represented as arrays
of char values. However multi-byte strings are much easier to manipulate since
the character are all of the same size.
Applications typically use wide characters to represent character codes
internally, and multi-byte strings when saving the characters to a file.
The gdk_wcstombs() and gdk_mbstowcs() functions can be used to convert from
one representation to the other.
See the 'Extended Characters' section of the GNU C Library Reference Manual
for more detailed information on wide and multi-byte characters.
gdk_wcstombs ()
Converts a wide character string to a multi-byte string.
(The function name comes from an acronym of 'Wide Character String TO
Multi-Byte String').
gdk_mbstowcs ()
Converts a multi-byte string to a wide character string.
(The function name comes from an acronym of 'Multi-Byte String TO Wide
Character String').