Re: Try time (decode) and size for null glyf/loca xform vs regular vs woff1

On Thu, May 19, 2016 at 3:01 PM, Levantovsky, Vladimir <
Vladimir.Levantovsky@monotype.com> wrote:

> Rod wrote:
>
> The brotli codebase is probably the most carefully optimized of the
> implementations I compared. WOFF2 without transform could likely be sped
> up, though some work is hard to dodge without violating the spec. For
> example, "the decoder MUST recalculate the checkSum value for each decoded
> table."
>
>
>
> Behdad wrote:
>
> But, browsers surely are allowed to skip that if they know the font will
> still work equally well.
>
>
>
> Not sure if this is feasible – the WOFF2 table directory doesn’t have
> checksum field and in many cases will only contain table flag and length.
> The reconstruction process essentially needs to rebuild SFNT table
> directory where checksum and offset will need to be recalculated regardless
> of whether a table was transformed or not – I don’t see how it can be
> skipped.
>

As far as I know, most of the widespread implementations don't care if
checksum is wrong, eg set to 0.  So, processes knowing this can skip
recalcing checksum.


>
>
> Thanks,
>
> Vlad
>
>
>
>
>
> *From:* Roderick Sheeter [mailto:rsheeter@google.com]
> *Sent:* Thursday, May 19, 2016 4:40 PM
> *To:* Behdad Esfahbod
> *Cc:* WebFonts WG
> *Subject:* Re: Try time (decode) and size for null glyf/loca xform vs
> regular vs woff1
>
>
>
> The reference implementation just always does it as that seems to be what
> the spec says. We could potentially do something like make that optional
> and flip it off in OTS I suppose?
>
>
>
> On Thu, May 19, 2016 at 1:36 PM, Behdad Esfahbod <behdad@google.com>
> wrote:
>
> On Thu, May 19, 2016 at 9:00 AM, Roderick Sheeter <rsheeter@google.com>
> wrote:
>
> As requested in https://www.w3.org/Fonts/WG/track/actions/186 I ran a
> variety of compress/decompress scenarios over the Google Fonts collection.
>
>
>
> Main findings are:
>
>
>
>  * WOFF2 decompression uses less memory than woff, more than brotli
> standalone.
>
>
>
>  * WOFF2 decompression was faster than WOFF at min, median, and average
> but has a higher standard deviation and max.
>
>
>
>  * Applying brotli (using the "bro" utility;
> https://github.com/google/brotli/blob/master/tools/bro.cc) directly to a
> font (to simulate use via Accept-Encoding: br) resulted in a file that was
> larger than a transformed woff2 but fastest to decompress.
>
>
>
>  * WOFF2 decompression is slightly faster when there are no transforms.
> The most significant improvement is lower standard deviation and worst-case
> time.
>
>
>
> The brotli codebase is probably the most carefully optimized of the
> implementations I compared. WOFF2 without transform could likely be sped
> up, though some work is hard to dodge without violating the spec. For
> example, "the decoder MUST recalculate the checkSum value for each decoded
> table."
>
>
>
> But, browsers surely are allowed to skip that if they know the font will
> still work equally well.
>
>
>
> Summary and raw results can be seen in
> https://docs.google.com/spreadsheets/d/1_ZYTFaG6_NJy7n_t-RpPDXCAZIKDP_1SXiJQz0o8QMg/edit#gid=367643030
> .
>
>
>
> Cheers, Rod S.
>
>
>
>
>