fdsc
table in the
sfnt
resource in a QuickDraw GX font. A font may have
any number of descriptors.fdsc
tags with
user functionality in mind.So far, the following five tags have been defined:
nalf
Non-Alphabetic FormsFor non-alphabetic fonts, the nalf
descriptor
indicates what class of non-alphabetic forms is provided by a font.
The defined values are simply those for the "Ornament Sets" feature
type:
Any additions or changes to that list should be reflected
here.
A nalf
which is zero or undefined means the font is
alphabetic. A style-matching scheme might look first for a matching
nalf
font type, and only then attempt to match the other
font descriptors.
opsz
Optical sizeOptical size is the output size which is best for the design of
the font. For a family with multiple design sizes, the
opsz
descriptor could be used for style matching. In the
absence of other information, the recommended optical sizes for Roman
fonts are 12 point for text and 24 point for display.
slnt
SlantSlant is the font's angle right of vertical, expressed in degrees.
For upright Roman fonts, slnt
should be 0.
wdth
WidthValues for width range from 0.0 to 32767.0, centered on 1.0.
Width is a ratio relative to the center of the family. The regular or
default face has, by definition, a width of 1.0. Typical "condensed"
values are 0.7-0.85, and typical "extended" values are 1.2-1.3.
The recommended measurement method uses the total length of the
Shannon Text in mixed-case setting. That text is:
The Head And In Frontal Attack On An English Writer That The Character Of This Point Is Therefore Another Method For The Letters In A Time When Whom Ever Told The Problem To An Unexpected.
(All characters, including the period and space characters, are
included in the measurement.) These words represent the frequency of
letters in typical English.
wght
WeightValues for weight range from 0.0 to 32767.0, centered on 1.0.
Weight is a ratio relative to the center of the family. For Roman
faces, weight is typically measured by the thickness of vertical
strokes. The regular or default face has, by definition, a weight of
1.0. Typical "bold" values are 1.5-2.0.
Apple does not recommend any particular method of measuring weight.
A manufacturer may want to include other pieces of metric information with its fonts. To accommodate these, register additional descriptor tags with Apple via the address
fontregistry@applelink.apple.com
For instance, Adobe, ElseWare, and others use "color" metrics, which
assign an absolute "color" value to a typeface, independent of where
it lies relative to other members of its family. "Color" in this
sense combines elements of weight and width. Apple can accommodate
these "color" metrics by defining a specific descriptor tag for each
scheme, allowing the font manufacturer to include whatever additional
metric information they wish.