- From: John Hudson <tiro@tiro.com>
- Date: Mon, 29 Mar 2010 10:22:46 -0700
- To: John Daggett <jdaggett@mozilla.com>
- CC: www-style list <www-style@w3.org>
John Daggett wrote: >> Is the method of simulation specified or recommended? In theory, there >> is font info that can be used to define best scaling and positioning for >> simulated superscript and subscript; in practice, in a lot of fonts (the >> majority?), this information is not accurately set. It's one of those >> vicious circles in which app makers ignore the data, discouraging font >> makers from taking the time to calculate best values, which in turn >> discourages app makers from making use of them. > Ideally this would be specified normatively so that it would be as > consistent as possible across user agents. If you have the details > for how this should be done or can point me at a reference for this, > that would be great. I was planning on experimenting with this once > we have a partial implementation up and running. The in-font scaling and offset positioning values for inferior/superior simulation are located in the OS/2 table [1]: ySubscriptXSize ySubscriptYSize ySubscriptXOffset ySubscriptYOffset ySuperscriptXSize ySuperscriptYSize ySuperscriptXOffset ySuperscriptYOffset My recommendation would be to use these values to simulate inferior and superior glyphs, since if these values have been intelligently set by font makers they will provide the best possible relationship between simulated glyphs and <subs>/<sups> feature variant glyphs. As I mentioned earlier, in a lot of fonts these values are not intelligently set by font makers -- and I'm guilty of this too --, but in general this won't mean that the values are 'wrong', only that they're not optimal. I suspect a lot of font makers simply leave these values as e.g. FontLab defaults, so the simulated glyphs will at least be scaled down and lowered/raised accordingly. [Note to Adam and other font tool makers: it would encourage correct setting of these values if there were some way to preview the results inside the tool.] Doubtless there a number of fonts in which these values are completely wrong and will produce unacceptable results. But I don't anticipate that number being large, and this is easily classed as a font bug and not something that browser makers should have to worry about. If use of these values for simulated inferior/superior glyphs is specified normatively in CSS, I can make a strong case to my colleagues that we need to start giving these values more attention, especially in web fonts. John Hudson [1] http://www.microsoft.com/typography/otspec/os2.htm
Received on Monday, 29 March 2010 17:23:20 UTC