Why doesn't my font seem to work (or appears in red)?

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martin
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Why doesn't my font seem to work (or appears in red)?

Post by martin » 2007-07-31 14:39:21

Sometimes if you are working in Nisus Writer Pro/Express you may select a particular font but the characters don't change their appearance. If working in Pro the name of the font will appear in red in the menu (this color is customizable in your preferences). Why is this? Why doesn't Nisus Writer respect your choice of font?

The problem is that all fonts do not contain all characters. For example, the Courier font cannot display a Hebrew Aleph or CJK ideograph for zero. If you apply Courier to these characters then Nisus Writer must choose another font for display that does contain these characters. This process is called font substitution.

You can somewhat customize this process in Nisus Writer's Language preferences. Each language has a secondary font setting. If a font cannot display the characters it is applied to then Nisus Writer will first try to use the secondary font you've chosen. Only if the secondary font also cannot be used will an arbitrary backup font be selected.


Classic Mac Fonts
Nisus Writer uses Unicode internally to represent characters. In Unicode virtually every character in the world has a unique number assigned to it. This ensures that your text is never misunderstood by another Unicode compliant application. This mapping of characters to numbers is called a text encoding; that is, given a particular number (eg: 107) an application knows what corresponding character to display.

The problem is that Unicode wasn't around yet during the Classic Mac era. Fonts created for use on OS9 all used the same numbers (0-255) to represent different characters. Thus a particular number may display as a latin "A" in one font, but a Greek "alpha" in another. If you changed the font, or worse yet, lost the font, the meaning of your text could be destroyed.

This situation is also why your old fonts may not work with Nisus Writer Pro/Express. These fonts only know how to display characters that use the Classic Mac encoding. So if you type a Hebrew aleph in OSX the character is encoded using the number 1488. Classic fonts have no knowledge of this number and thus font substitution must occur.

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