Re: default 'line' for vertical cues in VTT?

On Wed, Jul 23, 2014 at 1:26 AM, David Singer <singer@apple.com> wrote:
> For vertical:rl meaning vertical with right to left line progression, is a new cue without a line cue setting at the right of the video area or the left? This would be analogous to horizontal layout having first lines appear at the “bottom” of the screen, bottom here being the opposite of “right”.
>
> Likewise, for vertical:lr, is it left or right?
>
> For horizontal cues where “vertical:” is not specified, the WebVTT spec is clear. It’s at the bottom of the video area.
>
>
> Item 3 under “A line position” says:
>
>         3. If the text track cue snap-to-lines flag of the text track cue is not set, return the value 100 and abort these steps. (The text track cue line position is the special value auto.)
>
> This might mean bottom for horizontal, leftmost for “vertical:rl” and rightmost for “vertical:lr” but…does it?
>
>
>
> * * * *
>
>
> Does anyone have an opinion, fact, existing implementation, cultural knowledge of what’s normal, or anything else relevant?
>
> Thanks

I'll assume we're talking only about snap-to-line cues here.

When no explicit line is set, the line is auto, which means the
"computed line position" will be -1 if there are no other enabled
tracks.

So, what does line:-1 mean for vertical growing left and vertical
growing right cues? Search for "computed line position" in
http://dev.w3.org/html5/webvtt/#rendering to find the relevant bits.

You'll find that the x-position is inverted for vertical growing left
vs right, so that indeed it works as you would expect: vertical
growing left starts at the right edge and grows to the left, and vice
versa.

The spec does some things related to lineAlign here which I don't
believe has been implemented anywhere. Existing implementation are
likely closer to
http://web.archive.org/web/20130405025312/http://dev.w3.org/html5/webvtt/#rendering

HTH

Philip

Received on Wednesday, 23 July 2014 09:31:40 UTC