RE: [woff2] should decoder sort tags alphabetically in table directory? (#3)

Hi Rod, all,

Happy New Year! Let’s kick it off with the good discussion during the call tomorrow.

Regarding the table order – there are two things here to consider:

1)      Table directory, where the table entries have to be sorted in alphabetical order of table tags, and this can _only_ be done by the decoder since the table directory is built on the fly when a woff2 font is decompressed and recreated.

2)      The order of the font tables in the font file – there is a recommended order specified by the OpenType specification, and this is again should be done by the decoder when the output font file is written. Checking the input font table order (and reordering them if necessary) in the encoder won’t hurt anyone but I doubt it would make the decoder job easier - it is still the decoder responsibility to ensure that the output font file is written using the recommended table order. The spec is silent about it so, technically, reordering font tables in the encoder has no effect on compliance.

In fact, it may be beneficial to look at the table order before compressing it with Brotli to see if grouping  certain tables together would improve compression efficiency. If so, the reordering of font tables in the encoder could be done for different reasons and the actual order of the tables in the compressed stream may differ from what is recommended by the OpenType spec.

Thank you,
Vlad


From: Roderick Sheeter [mailto:rsheeter@google.com]
Sent: Tuesday, December 30, 2014 3:43 PM
To: WebFonts WG
Subject: Fwd: [woff2] should decoder sort tags alphabetically in table directory? (#3)

FYI, Cosimo Lupo suggests that we are doing table re-ordering in the encoder when the spec says we should do it in the decoder. It appears to me that this is correct and we should update the decoder.

Should an encoder should be allowed to re-order if it is so inclined? - I don't immediately see why not.

---------- Forwarded message ----------
From: Behdad Esfahbod <notifications@github.com<mailto:notifications@github.com>>
Date: Sun, Dec 28, 2014 at 11:14 PM
Subject: Re: [woff2] should decoder sort tags alphabetically in table directory? (#3)
To: google/woff2 <woff2@noreply.github.com<mailto:woff2@noreply.github.com>>
Cc: rsheeter <rsheeter@google.com<mailto:rsheeter@google.com>>


I also agree that this sounds like the right thing to do. Thanks! @rsheeter<https://github.com/rsheeter>

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