Some parts of the text rendering code would be easier if glyphs forming a single character would be grouped. However this need to be done in a careful way to avoid performance regressions. Especially the overhead of creating a list for the common case of one glyph per character should be avoided.
@herm - is this already done or still needing to be done?
@springmeyer Judging by https://github.com/mapnik/mapnik/blob/master/include/mapnik/text/layout.hpp#L119-121 it looks like this hasn't been implemented yet.
Implementation of grapheme clusters in Blink https://chromium.googlesource.com/chromium/blink/+/c7b6a4caa92df8d9c2d61e70a85564e84d635ab1%5E!/