[luatex] Indic scripts

[Arthur Reutenauer]

	Hi Mike,

  Any kind of rendering is outside of LuaTeX’s scope and has to be done
at the macro package level, which is what is done in ConTeXt for a
number of scripts but, as you’ve found out, not for most Indic scripts
(though to my knowledge Devanagari rendering has been implemented).  The
ConTeXt code that does the rendering is also used in LaTeX via a number
of packages, so that LaTeX supports exactly the same scripts as ConTeXt.

> Unfortunately, we discovered at the very end of this project that LuaTeX is
> mis-rendering Tamil text.

  It’s unfortunate that you embarked in a project that includes texts in
Tamil and Bengali without checking whether LuaTeX was able to render it
properly.  The LuaTeX project has always been very clear, from the
beginning, that LuaTeX wouldn’t do any rendering at all.  This is by
design.

> Is this on someone's radar?  It effectively makes it impossible to render
> text in complex scripts using LuaTeX.  It works correctly in XeTeX,
> presumably because XeTeX uses a different rendering engine to create the
> PDF.

  That’s correct, XeTeX uses Harfbuzz that is embedded in the engine;
that is to say that XeTeX itself can do the rendering and does not rely
on macro packages.  There is regular talk of libraries or macro packages
that could interface Harfbuzz with LuaTeX, but nothing concrete has come
out of it (yet?).

	Best,

		Arthur