![]() Use this strategy if you want to do the minimum amount of work, keep things simple, and eliminate clipping. For those alternate strategies see the Glyphs vertical metrics tutorial and John Hudson’s technique. There are legitimate reasons you might consider setting these to some other value, but we don’t recommend it unless you have a specific purpose. One area of strong agreement is that LineGap/sTypoLineGap be set to zero. These strategies almost exactly match what Google recommends in their vertical metrics specification. The following three strategies can be used to address both goals. Your secondary goal is to give the font reasonable default line spacing. Since you don’t have direct control over default line spacing everywhere, your primary goal is to avoid situations where some unkind OS or app does something really bad, such as cutting off the tops or bottoms of your letters. You may, however, set the numbers differently if you have separate font families. If they are not the same, then selecting a word in a paragraph and making it bold or italic may change the line spacing for just that one line-a frustrating and ugly problem. Some font testing tools report a mismatch between family members as a technical error. Keep the ascender and descender values the same across a font family (R, B, I, BI). Recent CSS proposals also hint that setting these correctly in the font will enable improved layout alignment for things like drop caps. ![]() ![]() The Cap height and x-height values in some font design programs are not used directly by apps, but setting them correctly might be helpful, as they may be used as guidelines. This bit should be set for all fonts, even though some old software (e.g. In FontForge set the Really use Typo metrics box. In FontLab check Prefer typo metrics in File > Font Info > Other Values > Family dimensions. In Glyphs you set this by adding a Use Typo Metrics custom parameter. Setting this bit tells applications to use the sTypo* values for line spacing. There is an additional parameter in the OS/2 table-bit 7 of fsSelection-that affects line spacing. All the eight values above are instead set in Element > Font Info > OS/2, including the hhea values. There is a restriction in FontForge that enforces that Ascent + Descent = Em Size, which is unnecessary. FontForge is particularly misleading: Element > Font Info > General has Ascent and Descent fields, but those are best ignored. FontLab also provides access to individual vertical metrics. However, setting optimum line spacing metrics requires manually overriding these settings through Custom Parameters (see Glyphs vertical metrics tutorial). Glyphs tries to make line spacing easy to set and simplifies this to two settings in the Font Info/Masters panel: Ascender and Descender, which it uses to set all the others. It is important to set all eight of these values sensibly in order to minimize inconsistencies and problems in line spacing and clipping across a variety of environments. Unfortunately some apps misused usWin* to also set line spacing. The OS/2 usWin* values were initially intended to determine clipping-meaning that any part of the glyph that extends above usWinAscent, or below usWinDescent, could get chopped off. The OS/2 sTypo* values were added later by Microsoft and are the ones most apps should be using today. The hhea values are the historically oldest, originally established by Apple. OpenType has a variety of internal metrics, stored in the hhea and OS/2 tables, that are used by many operating systems and applications to determine default line spacing: However it is important to try and make it as consistent as is reasonable, and to provide good default spacing. There is no technical means of specifying a consistent default line spacing across all environments from within the font. ![]() Whenever possible, line spacing should be set explicitly by the user rather than relying on an application’s defaults. Many also have a way to explicitly (manually) set the line spacing to a certain amount. Others, such as InDesign, simply set it at a percentage of the point size, usually 120%. Some programs look inside the font for information. Each program has a built-in way of automatically guessing at a good default line spacing, but those techniques differ. Most word processors and page layout programs have two ways of setting line spacing (how far apart vertically two lines of text will be)-automatic and manual (“exactly”).
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