2.8 KiB
Title
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| Fonts and Glyphs |
Fonts
Pango supports a flexible architecture where a particular rendering architecture
can supply an implementation of fonts. The PangoFont structure represents an
abstract rendering-system-independent font. Pango provides routines to list
available fonts, and to load a font matching a given description.
Conceptually, Pango groups fonts into faces and families which are identified by a name. A font face provides the different sizes of a single font style. A font family provides the available styles of a font.
As an example, "Helvetica" is a family, "Helvetica Bold" is a face of this family, and "Helvetica Bold 12pt" is a concrete font of this face.
Font Enumeration
The central object for dealing with the available fonts on a system and caching loaded fonts is a [class@Pango.FontMap]. An application typically uses a single font map.
Since the font map depends on the rendering architecture in use, you'll need to
use the backend function pango_cairo_font_map_get_default() to obtain the default
fontmap. Depending on the platform, it will return a PangoCairoFcFontMap, a
PangoCairoWin32FontMap or a PangoCairoCoreTextFontMap.
Once you have a fontmap, you can enumerate the available font families with [method@Pango.FontMap.list_families]. To enumerate the faces of a font family, use [method@Pango.FontFamily.list_faces].
Font Descriptions
Since loading fonts uses system resources, Pango provides a way to describe a font without loading it. A [struct@Pango.FontDescription] is a struct that contains enough information to load a concrete font with [method@Pango.FontMap.load_font] or [method@Pango.Context.load_font]. You can obtain a font description from a font face using [method@Pango.FontFace.describe], or by parsing a string such as
Helvetica Bold 12pt
with [func@Pango.FontDescription.from_string].
Glyphs
A font provides information about glyphs and how to position and render them. The Pango rendering pipeline uses this information to create a [struct@Pango.GlyphString], which contains the glyphs corresponding to the characters in the text and related information such as glyph positions and sizes, and clustering information (i.e. which glyphs correspond to which characters).
A glyph is identified by a [alias@Pango.Glyph], which is a numeric ID. Note that glyph IDs are font-specific: the same character can be represented by diffferent glyph IDs in different fonts.
The mapping between characters and glyphs is in general neither 1-1 nor a map: a single glyph may represent multiple characters (as is the case with ligatures), a single character may be represented by multiple glyphs (for example, when combining accents and base character), and in complex scripts, multiple characters may form clusters that get rearranged and represented by multiple glyphs.