Re: mkiv vs. mkii

[Taco Hoekwater <taco@elvenkind.com>]

Hi Mika,

Mika Ritola wrote:
> 
> Could you explain what mode=node does? I've seen it mentioned many times but
> I still don't know what its purpose is. I searched the ConTeXt site (using
> the search box), and didn't find any other useful information on it except
> that it affects kerning, but how? What are the advantages and disadvantages
> of using it? When should you use it?

Mark IV has two font processing modes, 'base' and 'node'.

In base mode, the font metrics are transformed into a traditional
tfm-style table, which means that all kerning and ligaturing is
handled by the core luatex engine. This is very similar to the
processing that takes place mkii (pdftex). Its advantage is that
it is faster than node mode, but the disadvantage is that you do
not have access to any of the advanced features in opentype fonts.

In mode node, the font metrics is transformed into a table that
has no kerning nor ligatures at all, and the kerning and ligature
processing is handled by the mkiv lua code instead of the core engine.
The advantage is that you can do much more advanced stuff (for example,
node mode is required for on-the-fly feature changes, all non-trivial
ligature replacements, and for non-latin scripts) but the disadvantage
is that processing is slower.

Currently mkiv defaults to base mode except for the predefined
fontfeatureset 'arabic', but this may change in the future, IIRC.

Best wishes,
Taco
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