![]() One of the proponents of letting go of the UPM dogma was Victor Gaultney from SIL, who wrote both Best Practice: Design Metrics and Best Practice: Line Metrics. This used to make things really complicated.Ī few years ago, the ‘UPM dogma’ has gotten under fire, because it simply did not work for scripts that require different metrics than Latin. In the dark past of electronic typesetting, the TrueType/OpenType specifications used to stipulate that the span from typoAscender to typoDescender should be as large as the font’s UPM (usually 1000 or 2048). There is one thing you need to watch out for, though: the ‘UPM dogma’. In that case, typoLineGap will be respected as well. Office software and browsers should prefer the typo values over win if the Use Typo Metrics parameter is set to yes. In DTP apps, the line gap is set by the user, hence typoLineGap is ignored. The big layout apps, XPress and InDesign, use the typoAscender and typoDescender values to determine the offset of the first baseline in a text box and the minimum size of a text box below which the display of type is suppressed. ![]() Windows supposedly uses these values to find the ideal parameters for layout thus we have a certain degree of artistic freedom.’ To quote Yannis Haralambous (p.724), these values ‘are oddly similar to ascent, descent, and lineGap in the hhea table but that should not necessarily be so precise or so closely tied to the vagaries of the glyphs’ outlines. ![]() typoLineGap: the recommended whitespace between lines.typoDescender: the depth of the descenders in units (negative value).typoAscender: the height of the ascenders in units.I have seen designers refer to them as OS/2 values, but that is a little imprecise, because the win values are also part of the OS/2 table. Sometimes, they are also referred to as sTypo or simply typo values, though. Anybody remember the operating system by the same name? Type pros commemorate it every day, thanks to vertical metrics. These values are part of the OS/2 OpenType table. hheaLineGap: the recommended whitespace between lines.hheaDescender: the depth of the descenders in units (negative value).hheaAscender: the height of the ascenders in units.For convenience, I will list them here with the custom parameter names that Glyphs uses: The hhea table knows three vertical metrics values. Apple devices such as Macs, iPhones, iPads, etc., use these values for rendering. ‘hhea’ is supposed to be an abbreviation for ‘horizontal typesetting header’. The name hhea refers to the hhea OpenType table. Set the values in one master, then copy and paste the parameters into the Custom Parameters fields of all other masters.īut what do these values mean? Let me give you a quick rundown. You will do this with custom parameters in File > Font Info > Masters (Cmd-I). So, in order to avoid vertical jumps when you switch between different fonts of your family, it is a good idea to synchronize all values across all masters. You may run into problems, however, if these values change between masters. Fortunately, Glyphs does its best to calculate them based on the vertical metrics you enter for each of your masters: ascender, cap height, x-height and descender. Unfortunately, all of these values relate to each other in a pretty complicated way. ![]() Depending on which OS you’re on and which application you’re in, a different set is used for rendering the font on the screen. sTypo or OS/2) and win (or usWin) metrics. For historical reasons, there are no less than three sets of values that deal with your vertical metrics. ![]()
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