[lucida] Large braces, question and/or feature request

Bruno Voisin bvoisin at me.com
Wed Apr 3 11:06:45 CEST 2013

Hi Tobias,

> There are currently no large curly braces in Lucida Bright Math OpenType and this "issue" is nothing one can "fix" in TeX but rather something that can only be taken care of by adding new glyphs to the font.

I was just looking at that when your message arrived. The following is probably obvious for the experts here, but I had never looked at it so far.

Lucida Type 1 followed CM's footsteps, by having:

- Small braces in the Math Symbol font (cmsy10 and lbms) at positions

	"66 "67

- Larger braces at four increasing sizes in the Math Extension font (cmex10 and lbme) at positions

	"08 "09
	"6E "6F
	"1A "1B
	"28 "29

All braces larger than that are built by assembling elements also from the Math Extension font, probably in the "3x range.

The TeXbook on p. 156 says, taking the example of the left parenthesis:

"[…] the small variant of a left parenthesis is found in position "28 of family 0 [cmmi], and […] the large variant is in position 0 of family 3 [cmex] […]. There actually are several different left parenthesis symbols in family 3; the smallest is in position 0, and the others are linked together by information that comes with the font."

The way in which a specific size in this predesigned set of braces is picked up is said to be discussed in Appendix G of the TeXbook. Only for the very brave of heart.

Now, Lucida OpenType in this respect seems to essentially have repackaged those characters from the Type 1 fonts. In particular, there are the same four predesigned brace sizes (as seen for example in FontForge):

> If the above is correct, I really would like to make a feature request: Some means to ensure a consistent look of braces of a greater variety of sizes, that is,
> - addition of glyphs for large curly braces in Lucida Bright Math OpenType just as in MathTimesPro or Cambria Math, or
> - addition of glyphs for small straight braces and a font feature to enable/disable them.
> However, you should note that I'm neither a designer nor a font creator: I have no clue how bad inconsistent braces really are from a designer's point of view nor do I know how complicated it is to add glyphs to Lucida Math OpenType.

Having braces created in the above way wasn't a problem for CM, because the braces are straight at all sizes, either predesigned or not. So the transition from the predesigned to the assembled glyphs was smooth. But the existence of curly braces in Lucida (or MathTime Pro) raises the problem.

Creating the missing glyphs (small straight braces, large curly braces) as in MathTime Pro is one thing. But making TeX use these glyphs is another matter. Considering "traditional" TeX (TFM files and PFB fonts) I would guess that two things are required:

- Checking the algorithms in Appendix G of the TeXbook, to make sure that the additional sizes would be used.

- Checking maybe in the TFM files that the various sizes are linked with one another (I imagine TFM files are what Knuth means when writing "information that comes with the font").

That seems far from trivial. Inspecting how things are done in MathTime Pro would probably help.

But with Lucida OpenType the problem becomes entirely different. I would guess that support from both the OpenType code within the font (for linking the sizes together) and the unicode-math package (for ensuring that the appropriate size is used) would be required. But that's really only a guess. And of how this could be done I have no idea.

So eventually I don't know whether the above really helps.

Bruno Voisin

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