Kerning feature for Malayalam fonts

At SMC, we’ve been continuously working on improving the fonts for Malayalam – by updating to newer opentype standard (mlm2), adding new glyphs, supporting new Unicode points, fixing shaping issues, reducing complexity and the compiled font size, involving new contributors etc.

Recently, out of scratching my own itch, I decided that it is high time to fix the annoyance that combination of Virama(U+D04D ് ) with quote marks (‘ ” ‘ ’ “ ” etc) used to overlap into an ugly amalgam in all our fonts. Usually Virama(് ) connects/combines two consonants which makes all 3 into a new glyph – for example സ+്+ന is shaped into a new glyph സ്ന (Note that you need a traditional orthography font installed to see the distinction in this example. Many of them are available here) . The root of the problem is that sometimes when Virama(് ) appears individually in a word such as “സ്വപ്‌‌നം” it connects two consonants പ and ന, it is positioned above the x height of most glyphs and it shall not have much left and right bearing to avoid ugly spacing between the consonants പ and ന.  Because of small side bearings, in fact of the negative right bearing (് protrudes beyond the right bearing) when a quote mark follows it, quote mark gets a little juxtaposed into Virama glyph and renders rather bad. The issue is quite prominent when you professionally typeset a book or article in Malayalam using XeTeX or SILE.

Fontforge’s tools made it easy to write opentype lookup rules for horizontal pair kerning to allow more space between Virama(് ) and quote marks. You can see the before and after effect of the change with Rachana font in the screenshot.


Update 26/03/2016: Many applications already support the kerning feature out of the box, including Firefox, SILE and VLC (3.0.0-git for subtitles) that I have tested, but many still need support, for instance LibreOffice, Kwrite etc. Here is a screenshot of VLC (3.0.0-git) taking kerning rules into account while displaying Malayalam subtitle.


Other fonts like AnjaliOldLipi, Meera and Chilanka also got this feature and those will be available with the new release in the pipeline. I have plans to expand this further to use with post-base vowels of വ(്വ) and യ(്യ) with abundant stacked glyphs that Malayalam has.


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