[luatex] Font expansion and virtual fonts

Hans Hagen pragma at wxs.nl
Fri Feb 9 10:49:04 CET 2018

On 2/9/2018 10:34 AM, Patrick Gundlach wrote:
> Hello all,
> I always come up with vague question, so here is another one.
> I use a virtual font to re-encode a real font and it seems that font expansion is not used anymore. Is this a well known thing? Both fonts (the real font and the virtual font) have the same parameters stretch/shrink/step, auto_expand and expansion_factor for each glyph.
> (If no, then I will try to sort out and try to make a small test case)
Font expansion looks at a glyph and its properties. It actually is not 
interested in what that glyph is and only the expansion factors and 
width matters. So, you need to make sure that these properties are set. 
The multiplication factor travels with the glyphs after the paragraph 
has been calculated. In the (back)end what gets injected are just kerns 
based on these factors.


ps. The implementation is not the same as in pdftex in the sense that no 
extra pseudo fonts are generated, not are expansion factors calcualted 
on the fly each time (they are glyph property).

                                           Hans Hagen | PRAGMA ADE
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