Fonts Loading and manipulating fonts 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 substituted 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, GDK 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. 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. Indicates the type of a font. The possible values are currently: @GDK_FONT_FONT: the font is a single font. @GDK_FONT_FONTSET: the font is a fontset. @font_name: @Returns: @display: @font_name: @Returns: @fontset_name: @Returns: @display: @fontset_name: @Returns: @font_desc: @Returns: @display: @font_desc: @Returns: @font: @Returns: @font: @Returns: @font: @font: @Returns: @fonta: @fontb: @Returns: @font: @string: @lbearing: @rbearing: @width: @ascent: @descent: @font: @text: @text_length: @lbearing: @rbearing: @width: @ascent: @descent: @font: @text: @text_length: @lbearing: @rbearing: @width: @ascent: @descent: @font: @string: @Returns: @font: @text: @text_length: @Returns: @font: @text: @text_length: @Returns: @font: @character: @Returns: @font: @character: @Returns: @font: @string: @Returns: @font: @text: @text_length: @Returns: @font: @character: @Returns: @font: @string: @Returns: @font: @text: @text_length: @Returns: @font: @character: @Returns: 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. @src: @Returns: @dest: @src: @dest_max: @Returns: