Terminology
Version 6.1.0
In this article
This article defines the meaning of terms used in PDFsharp in connection with font management. For a general introduction on typography see Microsoft Typography documentation.
Font
Generally in typography a font is a complete character set in a particular point size, in a particular typeface. A computer font is a file that contains a set of characters in a particular style of a typeface. Over the decades a lot of font technologies have been developed, like bitmap fonts, vector fonts, etc. The only fonts supported by PDFsharp are OpenType fonts.
E.g. in Windows the file ARIALBD.TTF contains a large set of glyphs of the font Arial with the style bold.
The meaning of the term font depends on the context of use. Sometimes it refers to the font family (e.g. 'Arial'), the font file (e.g. 'arial.ttf'), the font face (e.g. 'Arial narrow italic'), or the typeface (also 'Arial'). In this documentation font always means font face.
Font face
A font face, often just called font, is the manifestation of a particular typeface.
In computer typography a font face is typically represented by a font file.
Arial comes with 4 font faces: Arial (regular), Arial bold, Arial italic, and Arial bold italic.
E.g. the typeface Segoe UI Semibold Italic is in Windows manifested in the font face stored in file SEGUISBLI.TTF.
This file is an OpenType font file with TrueType outlines.
However, a font file can contain more than one font face if it is an OpenType font collection.
Font family
A font family is a collection of fonts (font faces) that share particular design features within a specific style of typeface. A font family shares common properties of all its fonts like line spacing. E.g. the font family Segoe UI includes 12 font faces, while the family Segoe UI Emoji contains only one face.
Typeface
A typeface refers to a complete set of characters that are unified by a common design ethos. Typeface and font or font face are often used similarly. In general, a typeface is something more abstract about the visual appearance while a font is a physical representation of a typeface. A typeface is what a font designer creates in their mind. A font is what was created from the typeface to actually print text. Ancient fonts were made of wood or lead (plumbum), while todays computer fonts are mostly OpenType fonts with e.g. TrueType glyph outlines. The following quote may clarify the different views on Arial.
A lot of font designers consider Arial a poor typeface, because it is (or at least looks like as) just an unambitious copy of Helvetica. On the other hand Arial is a high value font, because it comes with Windows in 9 different styles with tens of thousands glyphs for a lot of languages.
In computer font technology a typeface often is composed of four components that are used to map it to a font face.
- The family name, e.g. Segoe UI
- The style. Which is regular or italic. Sometimes also oblique, which is often used interchangeable with italic.
- The weight. It goes from thin to extra black. Historically Windows supports only normal and bold. WPF has built-in support of weight.
- The stretch. It goes from ultra condensed to ultra expanded. Historically Windows has no concept of it. WPF has built-in support of stretch.
Because Windows originally only supports italic and bold, even newly created typefaces come in 4 type faces per family. Typefaces with weight other than regular or bold, or stretches other than regular have to define new families with different names. Although Arial is typographically a font family of 9 typefaces, it is for the sake of Windows divided in 3 physical families. Arial with 4 faces (regular, bold, italic, and bold italic), Arial Narrow with also 4 faces and Arial black with one face.
See font resolving for information how PDFsharp maps typefaces to font faces.
em size
The em size specifies the size of a font.
The name refers to the small letter m.
PDFsharp measures the em size of a font in point, which is 1/72 of an inch.