Thank you for your reply, Jonathan. So I think GNUFreeFont should remove these constructions and perhaps group them into one largest size variant.
Le 17/04/2015 17:29, Jonathan Kew a écrit : > On 17/4/15 16:07, Frédéric Wang wrote: >> Hi all, >> >> Here is a testcase with a dev version of GNUFreeFont: >> http://fred-wang.github.io/MathFonts/GNUFreeFont/ >> >> As I understand, stretchy U+2F/U+2211/U+27E8/U+27E9 do not have a "glue" >> so we connect them using a rule >> >> https://dxr.mozilla.org/mozilla-central/source/layout/mathml/nsMathMLChar.cpp#855 >> >> >> but the rule thickness has the width of the parts, which leads to these >> ugly large rectangles. > > I don't see how a rule of *any* thickness would look good in the > middle of a character such as / or ∑. See below... > >> >> What do you think? Is it a bug due to our limited implementation of the >> MathVariants table (bug 963147)? Or is it incorrect for a font to >> specify a stretchy operator construction without any extender? > > ISTM this is incorrect. The spec[1] says that glyph assemblies are > used by: > > 1. Assemble all parts by overlapping connectors by maximum amount, and > removing all extenders. This gives the smallest possible result. > > 2. Determine how much extra width/height can be distributed into all > connections between neighboring parts. If that is enough to achieve > the size goal, extend each connection equally by changing overlaps of > connectors to finish the job. > > 3. If all connections have been extended to minimum overlap and > further growth is needed, add one of each extender, and repeat the > process from the first step. > > Step 3 here implies that at least one extender glyph should exist in > the assembly. Otherwise, it cannot be extended beyond the maximum size > achieved by step 2. > > Note also that extension can only happen, AFAICT, in a straight > vertical or horizontal line. It doesn't look possible to extend > diagonals; and therefore only variant glyphs, not extensible > assemblies, should be used for characters such as slash or Sigma. > > JK > > > [1] http://www.microsoft.com/typography/otspec/math.htm > > -- Frédéric Wang maths-informatique-jeux.com/blog/frederic