## bug #52240: Extensible math symbols

 Submitted by: Steve White Submitted on: Tue 17 Oct 2017 09:09:23 AM UTC Category: individual character(s) Severity: 3 - Normal Item Group: letter positioning poor Status: Fix posted Privacy: Public Assigned to: Steve White Open/Closed: Open Release: development

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Sun 22 Oct 2017 10:10:41 AM UTC, comment #1:

For the record: this is a messy business -- the OpenType MATH table is limited a couple of ways. The solution in I made isn't to my satisfaction.

There are several problems with extensible bracket symbols -- two of them related to font height.

First is the issue of glyphs with diagonals: slashes and angle-brackets. The "extension" mechanism provided by the MATH table can be applied to these only clumsily, by providing for double-size symbols consisting of two diagnonal parts. Most fonts don't bother with that instead making a set of ever-larger symbols for use in the "horizontal variants" table.

The result of making glyphs in a font that are two or three times the font height, is that much software will misbehave badly. This is the old problem of the early and persistent confusion as to the meaning of the height of the font. Such a font can't be termed general-purpose. In fact, some font families make a separate "math" face for just this reason. But that is a cludge.

It would be better if there were some way to construct a diagonal, by adding pieces offset diagonally somehow. But there appears to be no means of doing this, at this time.

The other problem related to font-height has to do only with the vertical variants. In the traditional LaTeX sequence "\big \Big \bigg \Bigg" of explicit bracket sizes, the \Big size is already some twice the height as the basic bracket. This can't be achieved with a normal-sized parenthesis within a font of reasonable font-height. One can try making four sizes of bracket and listing them in the vertical variants table, but LaTeX will only pick out one or two of them. Evidently it expects a coarser gradation of sizes.

Steve White <Stevan_White>
Tue 17 Oct 2017 09:09:23 AM UTC, original submission:

These are the extensible integral, parentheses, brackets, braces and summation U+2320 etc. U+239B.

In the previous release, these were made to work well with one another when aligned vertically with line spacing set to 1. (Stacked, say, using an HTML table, or in a monospaced console environment.)

A couple of years ago they were re-purposed for use in LaTeX, and entries were made for in the MATH table. In this role, different heights for the extension glyphs are appropriate. (The LaTeX application allows for finder adjustment of the heights of the extended symbols, so the connectors had to be much shorter -- for one thing.) This broke the original use of the glyphs.

The plan is to replace the glyphs with ones that work for the original purpose, and copy the newer glyphs into auxiliary slots, where they can be used in the MATH table.

Steve White <Stevan_White>

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