W3C home > Mailing lists > Public > public-texttracks@w3.org > April 2012

Re: Displaying multiple lines in WebVTT

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Wed, 18 Apr 2012 11:17:56 +1000
Message-ID: <CAHp8n2mnTOFg7g5UoVaZ90Oz3e5MfXgA8K0UsJKaSL-i1G2oog@mail.gmail.com>
To: Glenn Maynard <glenn@zewt.org>
Cc: Frank Olivier <Frank.Olivier@microsoft.com>, "public-texttracks@w3.org" <public-texttracks@w3.org>
On Wed, Apr 18, 2012 at 10:15 AM, Glenn Maynard <glenn@zewt.org> wrote:
> On Tue, Apr 17, 2012 at 4:45 PM, Silvia Pfeiffer <silviapfeiffer1@gmail.com>
> wrote:
>>
>> I've had a bit of a chat with some people on the Chrome team that work
>> on CSS and the balanced text wrapping mode that we are after indeed is
>> not easy to implement using CSS. It basically requires a new CSS
>> algorithm.
>
>
> Right, it belongs in CSS.  (I found the earlier discussion:
> http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2011-December/034026.html
> "basic algorithm should be ...".)
>
> It shouldn't be difficult--at least, no more difficult than any other
> wrapping algorithm.
>
>> We're considering this to be a new value for text-wrap - something
>> like "text-wrap: balance;". It would states something along the lines
>> of what you outlined - basically that it minimizes white space in the
>> last line of a multi-line paragraph by re-distributing this white
>> space over all lines and thus making the individual lines shorter. How
>> a browser implements this would be up to the browser.
>>
>> What we likely need to do is: write a proposal (in a wiki page or so)
>> for this new mode, explaining our use case. We should then send it out
>> to the www-style list for general discussion. If you are keen, do go
>> ahead with preparing such a proposal.
>
>
> I don't know if I'll have the bandwidth to explain this from scratch to yet
> another audience.  I'll try to get to it eventually if someone else doesn't
> get to it first...
>
> The suggested algorithm is:
>
> 1: Wrap the text using the ordinary word-wrapping algorithm, and let L be
> the resulting number of lines.
> 2: For each possible width W, starting at 1 and ending at the maximum
> wrapping width, do the following:
> 2.1. Wrap the text to width W, using the ordinary word-wrapping algorithm.
> 2.2. If the resulting number of lines is less than or equal to than L,
> return the wrapped text.  Otherwise, continue to the next possible width.
>
> This simply finds the narrowest width that doesn't require additional lines
> than ordinary wrapping.  This runs in linear time on the size of the input
> text.  (Of course, this can be optimized without changing the results, by
> performing a binary search on W instead of a linear one, but that's an
> implementation detail.)
>
> This may not produce great results for large paragraphs, but it should work
> well for caption-size text, where the common case is only a few lines.
>
> (Apparently this has been tried before, but it was attempting to find the
> *optimal* solution, which turns out to be O(n^2).  I believe this solution
> is more than adequate for WebVTT's needs, and good enough to be of general
> use; Ian mentioned headings, which this should work well for too.)

Sounds good to me!

I don't have the bandwidth right now to do this, but will put it on my
list for after the current task.

Cheers,
Silvia.
Received on Wednesday, 18 April 2012 01:18:49 GMT

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