Editing Metafont (section)

===Graphics===
Curves in Metafont are defined as [[cubic spline]]s, rather than quadratic, for greater versatility at the cost of more complex arithmetic.<ref>{{cite interview|last=Knuth|first=Donald|subject-link=Donald Knuth|interviewer=Advogato|title=Interview: Donald E. Knuth|url=http://www.advogato.org/article/28.html|date=January 25, 2000|access-date=January 13, 2016|quote=...the mathematics is really simple for a quadratic. The corresponding thing for a cubic is six times as complicated...|archive-url=https://web.archive.org/web/20090122043044/http://www.advogato.org/article/28.html|archive-date=January 22, 2009|url-status=dead}}</ref>

Unlike more common outline font formats (such as [[TrueType]] or [[PostScript#Font handling|PostScript Type 1]]), a Metafont font is primarily made up of strokes with finite-width "pens", along with filled regions. Thus, rather than describing the outline of the glyph directly, a Metafont file describes the pen paths. Some simpler Metafont fonts, such as the calligraphic mathematics fonts in the [[Computer Modern]] family, use a single pen stroke with a relatively large pen to define each visual "stroke" of the glyphs. More complex fonts such as the [[Roman type|Roman]] text fonts in the Computer Modern family use a small pen to trace around the outline of the visual "strokes", which are then filled; the result is much like an outline font, but with slightly softened corners defined by the pen shape.

Since the font shapes are defined by equations rather than directly coded numbers, it is possible to treat parameters such as aspect ratio, font slant, stroke width, [[serif]] size, and so forth as input parameters in each glyph definition (which then define not a single font, but a [[Meta (prefix)|meta]]-font). Thus, by changing the value of one of these parameters at one location in the Metafont file, one can produce a consistent change throughout the entire font. Computer Modern Roman illustrates many uses of this feature; a typical TeX installation includes a number of versions of the font in [[pitch (typewriter)|pitches]] from 5 to 17 cpi, with the stroke widths the same in all sizes (rather than increasing as the font is scaled up). In addition, the Computer Modern typewriter and [[sans-serif]] fonts are defined using essentially the same Metafont file as the Roman font, but with different global parameters.