nested contextual lookups in Noto Sans Devanagari series

[GoogleCodeExporter]

In version 1.03 of each of the following fonts:

  NotoSansDevanagari-Bold.ttf
  NotoSansDevanagari-Regular.ttf
  NotoSansDevanagariUI-Bold.ttf
  NotoSansDevanagariUI-Regular.ttf

GSUB lookup #24 (which is of lookup type 5.2) calls a number of type 5.x 
lookups; in other words, it is a contextual lookup that calls other contextual 
lookups.

This can be confirmed by inspecting the font in question with e.g. DTL OT 
Master - click on 'GSUB' lookup list and expand lookup #24.

This may or may not be a defect depending on one's interpretation of the 
OpenType Specification. It is my understanding that contextual lookups should 
always call non-contextual lookups!

Incidentally, I haven't yet checked the GPOS lookups in these fonts...

Original issue reported on code.google.com by aaron.tu...@soulobjectiverecords.com on 22 Nov 2014 at 9:26

[GoogleCodeExporter]

We are aware of this.  While it might be simpler and cleaner if the contextual 
lookups do not invoke other contextual lookups, we don't believe that doing 
this is wrong or against the standard or widely deployed implementations.  Did 
you happen to notice this not working on any implementation or otherwise 
misbehaving?

Original comment by behdad@google.com on 23 Nov 2014 at 10:53

• Changed state: WAI

[GoogleCodeExporter]

No, I have not noticed any explicit malfunctions, it just seemed anomalous:

(1) Although seemingly allowed by the OpenType specification itself, the rather 
comprehensive "Fonts & Encodings" by Yannis Haralambous indicates explicitly 
that contextual lookups should only invoke non-contextual lookups.

(2) Out of 1372 fonts analysed, only the above 4 fonts incorporate contextual 
GSUB lookups that invoke other contextual GSUB lookups, contrary to 
Haralambous; thus these 4 fonts do rather seem to be going against the 
established norm.

No harm in pointing it out! :-)

Original comment by aaron.tu...@soulobjectiverecords.com on 28 Nov 2014 at 8:51

[GoogleCodeExporter]

Thanks for the comment.  Didn't know that Yannis's book says they won't work.  
Well, they do.  This was discussed on the OpenType mailing list a while ago.

I agree there's no absolute need for them.

Roozbeh, can you follow up with Jelle to see why they were used?

Original comment by behdad@google.com on 6 Dec 2014 at 11:22