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Chapter 7. Fonts and Encodings > 7.1. Introduction

7.1. Introduction

Half of the job of (La)TeX as a typesetting system is to process the source document and to calculate from it the characters’ positions on the output page. But (La)TeX has only a primitive knowledge about these characters, which it basically regards as black boxes having a width, height, and depth. For each font these dimensions are stored in a separate external file, the so-called TeX font metric or .tfm file.

The character shapes that correspond to such a .tfm file come into play at a later stage, after (La)TeX has produced its .dvi file. Character placement information in the .dvi file and information about character shapes present in the .pk file or in outline descriptions (e.g., PostScript) are combined by a driver program that produces the character image on the output medium. Usually one driver program is needed for every output medium—for screen representation, a low-resolution laser printer, or other device. With TeX variants such as pdfTeX or VTeX that bypass the production of .dvi output and instead directly generate PDF or PostScript output, the situation is slightly different (but, as far as LaTeX is concerned, similar). In that case the character shapes are “added” when the underlying formatter produces the final output format. That is, the driver program is internal, but the basic concepts are identical.


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