Side effect of virtual fonts

Side effect of virtual fonts

[Ulrike Fischer]

I made two copies of luatex-fonts-demo-vf-1.lua named
vf-a.lua  and vf-b.lua 

(The original file can be found in
\context-minimals\context\tex\texmf-context\tex\generic\context).


In both copies I changed the three fonts the virtual font uses as
basis to "Arial".

In vf-b.lua I added after the for-loop which manipulates the
caracters this code: 

        f1.characters[98].width=3000000
        f2.characters[98].width=3000000
        f3.characters[98].width=3000000

        f1.characters[97]= nil
        f2.characters[97]= nil
        f3.characters[97]= nil

It has the expected effect when I use vf-b: It enlarges the width of
the "b" and removes the "a" from the font.

But it not only affect the vf-b-font, it also affects vf-a: If I
load vf-a *after* vf-b, it also loose the "a" and the width of "b"
is changed.

In a older version of context, where the lua used
"fonts.tfm.readanddefine" instead of the new
"fonts.constructors.readanddefine" I got an side effect too, but
only on the "a".


My questions are

1. Why do I get the side effect only when f1, f2 and f3 call the
same font? Chance (because of the math random) or something else?

2. How can I make a virtual lua-font which is free of such side
effects? 

3. I got errors when I tried to use the old version of the virtual
font with the newest context. Is "fonts.tfm.readanddefine" now
deprecated?

-- 
Ulrike Fischer 

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