Editing TeX (section)

===Metafont===
{{main|Metafont}}

Metafont, not strictly part of TeX, is a font description system which allows the designer to describe characters algorithmically. It uses [[Bézier curve]]s in a fairly standard way to generate the actual characters to be displayed, but Knuth devotes substantial attention to the [[font rasterization|rasterizing]] problem on [[Raster graphics|bitmapped]] displays. Another thesis, by [[John Hobby]], further explores this problem of digitizing "brush trajectories". This term derives from the fact that Metafont describes characters as having been drawn by abstract brushes (and erasers). It is commonly believed that TeX is based on bitmap fonts but, in fact, these programs "know" nothing about the fonts that they are using other than their dimensions. It is the responsibility of the device driver to appropriately handle fonts of other types, including PostScript Type 1 and TrueType. Computer Modern (commonly known as "the TeX font") is freely available in Type 1 format, as are the AMS math fonts. Users of TeX systems that output directly to PDF, such as pdfTeX, XeTeX, or LuaTeX, generally never use Metafont output at all.