Make sure that the given font is always available and that the characters
are pre calculated at the given size. This allow maximum speed when all the
often used combinations are available, as the character never have to be
rendered. This will take up some memory though (the pre-calculated glyphs
are not stored in the cache to make sure they are never released).
You first have to pass the size, and then the fontname, e.g.
SYSTEM-FONT-CALCULATED 10 Goudy Old Style