Fonts

GDK Reference Manual
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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:

Foundry	the company or organization where the font originated.
Family	the font family (a group of related font designs).
Weight	A name for the font's typographic weight For example, 'bold' or 'medium').
Slant	The slant of the font. Common values are 'R' for Roman, 'I' for italoc, and 'O' for oblique.
Set Width	A name for the width of the font. For example, 'normal' or 'condensed'.
Add Style	Additional information to distinguish a font from other fonts of the same family.
Pixel Size	The body size of the font in pixels.
Point Size	The body size of the font in 10ths of a point. (A point is 1/72.27 inch)
Resolution X	The horizontal resolution that the font was designed for.
Resolution Y	The vertical resolution that the font was designed for .
Spacing	The type of spacing for the font - can be 'p' for proportional, 'm' for monospaced or 'c' for charcell.
Average Width	The average width of a glyph in the font. For monospaced and charcell fonts, all glyphs in the font have this width
Charset Registry	The registration authority that owns the encoding for the font. Together with the Charset Encoding field, this defines the character set for the font.
Charset Encoding	An identifier for the particular character set encoding.

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()

`type`	a value of type GdkFontType which indicates whether this font is a single font or a fontset.
`ascent`	the maximum distance that the font, when drawn, ascends above the baseline.
`descent`	the maximum distance that the font, when drawn, descends below the baseline.

enum GdkFontType

typedef enum
{
  GDK_FONT_FONT,
  GDK_FONT_FONTSET
} GdkFontType;

Indicates the type of a font. The possible values are currently:

GDK_FONT_FONT	the font is a single font.
GDK_FONT_FONT	the font is a fontset.

gdk_font_load ()

GdkFont*    gdk_font_load                   (const gchar *font_name);

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.

`font_name` :	a XLFD describing the font to load.
Returns :	a GdkFont, or NULL if the font could not be loaded.

gdk_fontset_load ()

GdkFont*    gdk_fontset_load                (gchar *fontset_name);

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.

`fontset_name` :	a comma-separated list of XLFDs describing the component fonts of the fontset to load.
Returns :	a GdkFont, or NULL if the fontset could not be loaded.

gdk_font_ref ()

GdkFont*    gdk_font_ref                    (GdkFont *font);

Increase the reference count of a count by one.

`font` :	a GdkFont
Returns :	`font`

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.

font : a GdkFont

gdk_font_id ()

gint        gdk_font_id                     (const GdkFont *font);

Returns the X Font ID for the given font.

`font` :	a GdkFont.
Returns :	the numeric X Font ID

gdk_font_equal ()

gint        gdk_font_equal                  (const GdkFont *fonta,
                                             const GdkFont *fontb);

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.

`fonta` :	a GdkFont.
`fontb` :	another GdkFont.
Returns :	`TRUE` if the fonts are equal.

gdk_string_extents ()

void        gdk_string_extents              (GdkFont *font,
                                             const gchar *string,
                                             gint *lbearing,
                                             gint *rbearing,
                                             gint *width,
                                             gint *ascent,
                                             gint *descent);

Returns the metrics of a NULL-terminated string.

`font` :	a GdkFont.
`string` :	the NULL-terminated string to measure.
`lbearing` :	the left bearing of the string.
`rbearing` :	the right bearing of the string.
`width` :	the width of the string.
`ascent` :	the ascent of the string.
`descent` :	the descent of the string.

gdk_text_extents ()

void        gdk_text_extents                (GdkFont *font,
                                             const gchar *text,
                                             gint text_length,
                                             gint *lbearing,
                                             gint *rbearing,
                                             gint *width,
                                             gint *ascent,
                                             gint *descent);

Returns the metrics of a string.

`font` :	a GdkFont
`text` :	the text to measure
`text_length` :	the length of the text in bytes. (If the font is a 16-bit font, this is twice the length of the text in characters.)
`lbearing` :	the left bearing of the string.
`rbearing` :	the right bearing of the string.
`width` :	the width of the string.
`ascent` :	the ascent of the string.
`descent` :	the descent of the string.

gdk_text_extents_wc ()

void        gdk_text_extents_wc             (GdkFont *font,
                                             const GdkWChar *text,
                                             gint text_length,
                                             gint *lbearing,
                                             gint *rbearing,
                                             gint *width,
                                             gint *ascent,
                                             gint *descent);

Returns the metrics of a string of wide characters.

`font` :	a GdkFont
`text` :	the text to measure.
`text_length` :	the length of the text in character.
`lbearing` :	the left bearing of the string.
`rbearing` :	the right bearing of the string.
`width` :	the width of the string.
`ascent` :	the ascent of the string.
`descent` :	the descent of the string.

gdk_string_width ()

gint        gdk_string_width                (GdkFont *font,
                                             const gchar *string);

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)

`font` :	a GdkFont
`string` :	the NULL-terminated string to measure
Returns :	the width of the string in pixels.

gdk_text_width ()

gint        gdk_text_width                  (GdkFont *font,
                                             const gchar *text,
                                             gint text_length);

Determine the width of a given string.

`font` :	a GdkFont
`text` :	the text to measure.
`text_length` :	the length of the text in bytes.
Returns :	the width of the string in pixels.

gdk_text_width_wc ()

gint        gdk_text_width_wc               (GdkFont *font,
                                             const GdkWChar *text,
                                             gint text_length);

Determine the width of a given wide-character string.

`font` :	a GdkFont
`text` :	the text to measure.
`text_length` :	the length of the text in characters.
Returns :	the width of the string in pixels.

gdk_char_width ()

gint        gdk_char_width                  (GdkFont *font,
                                             gchar character);

Determine the width of a given character.

`font` :	a GdkFont
`character` :	the character to measure.
Returns :	the width of the character in pixels.

gdk_char_width_wc ()

gint        gdk_char_width_wc               (GdkFont *font,
                                             GdkWChar character);

Determine the width of a given wide character. (Encoded in the wide-character encoding of the current locale).

`font` :	a GdkFont
`character` :	the character to measure.
Returns :	the width of the character in pixels.

gdk_string_measure ()

gint        gdk_string_measure              (GdkFont *font,
                                             const gchar *string);

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().

`font` :	a GdkFont
`string` :	the NULL-terminated string to measure.
Returns :	the right bearing of the string in pixels.

gdk_text_measure ()

gint        gdk_text_measure                (GdkFont *font,
                                             const gchar *text,
                                             gint text_length);

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().

`font` :	a GdkFont
`text` :	the text to measure.
`text_length` :	the length of the text in bytes.
Returns :	the right bearing of the string in pixels.

gdk_char_measure ()

gint        gdk_char_measure                (GdkFont *font,
                                             gchar character);

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.

`font` :	a GdkFont
`character` :	the character to measure.
Returns :	the right bearing of the character in pixels.

gdk_string_height ()

gint        gdk_string_height               (GdkFont *font,
                                             const gchar *string);

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().

`font` :	a GdkFont
`string` :	the NULL-terminated string to measure.
Returns :	the height of the string in pixels.

gdk_text_height ()

gint        gdk_text_height                 (GdkFont *font,
                                             const gchar *text,
                                             gint text_length);

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().

`font` :	a GdkFont
`text` :	the text to measure.
`text_length` :	the length of the text in bytes.
Returns :	the height of the string in pixels.

gdk_char_height ()

gint        gdk_char_height                 (GdkFont *font,
                                             gchar character);

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().

`font` :	a GdkFont
`character` :	the character to measure.
Returns :	the height of the character in pixels.

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 ()

gchar*      gdk_wcstombs                    (const GdkWChar *src);

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').

`src` :	a wide character string.
Returns :	the multi-byte string corresponding to `src`, or NULL if the conversion failed. The returned string should be freed with g_free() when no longer needed.

gdk_mbstowcs ()

gint        gdk_mbstowcs                    (GdkWChar *dest,
                                             const gchar *src,
                                             gint dest_max);

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').

`dest` :	the space to place the converted wide character string into.
`src` :	the multi-byte string to convert, which must be null-terminated.
`dest_max` :	the maximum number of wide characters to place in `dest`.
Returns :	the number of wide characters written into `dest`, or -1 if the conversion failed.