freetypy.TT_OS2.typo_descender¶
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TT_OS2.
typo_descender
¶ The typographic descender for this font. Remember that this is not the same as the
TT_HoriHeader.descender
, which Apple defines in a far different manner.The suggested usage for
typo_descender
is that it be used in conjunction withTT_Header.units_per_em
to compute a typographically correct default line spacing. The goal is to free applications from Macintosh or Windows-specific metrics which are constrained by backward compatability requirements. These new metrics, when combined with the character design widths, will allow applications to lay out documents in a typographically correct and portable fashion.For CJK (Chinese, Japanese, and Korean) fonts that are intended to be used for vertical writing (in addition to horizontal writing), the required value for
typo_descender
is that which describes the bottom of the of the ideographic em-box. For example, if the ideographic em-box of the font extends from coordinates 0,-120 to 1000,880 (that is, a 1000x1000 box set 120 design units below the Latin baseline), then the value oftypo_descender
must be set to -120. Failing to adhere to these requirements will result in incorrect vertical layout.