[NTG-context] Incorrect math kerning

Hans Hagen pragma at wxs.nl
Mon May 30 18:01:01 CEST 2016


On 5/30/2016 4:56 PM, Ulrike Fischer wrote:
> Am Mon, 30 May 2016 09:35:25 +0200 schrieb Hans Hagen:
>
>> In cambria staircase kerns are used for this but they are not defined
>> for all (base) characters.
>
> Are this these values:
>
>    ["math"]={
>     ["kerns"]={
>      ["bottomright"]=36,
>      ["topright"]=17,
>     },
>    },
>
>
> ? If yes, how could one change them to check if other values gives a
> better result?

I looked into it a bit and found a few issues.

(1) i forgot to adapt the scaler to the new fontloader so i fixed that 
(no beta yet)

(2) the old (ff) loader makes up some values which is probably a side 
effect of the at that time missing spec; it's harmless and ok but 
results in different tables between old and new loader

(3) you're right about the spot to patch or add but keep in mind that 
you look at the packed font table, so in the end you end up with something:

         kerns = {
             [0x1D449] = { bottomright = { { kern = -200 } } }, -- it V
             [0x1D44A] = { bottomright = { { kern = -100 } } }, -- it W
         }

the amount of kerning is subjected to personal preferences e.g. lucida 
has way less bottom kerning than cambria for instance

attached a sample for italic V and W

- native lucida ot kerning
- native cambria kerning
- specified for other fonts

Hans


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                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
       tel: 038 477 53 69 | www.pragma-ade.com | www.pragma-pod.nl
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