[Bug 19178] New: Don't adjust position when snap-to-lines flag is not set

https://www.w3.org/Bugs/Public/show_bug.cgi?id=19178

           Summary: Don't adjust position when snap-to-lines flag is not
                    set
           Product: TextTracks CG
           Version: unspecified
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: major
          Priority: P2
         Component: WebVTT
        AssignedTo: ian@hixie.ch
        ReportedBy: lorettaguarino@google.com
         QAContact: dave.null@w3.org
                CC: mike@w3.org, public-texttracks@w3.org


The cue text rendering rules are different when snap-to-lines is set and when
it is not set. When it is not set:

1. The first step recalculates x and y, although snap-to-lines has already been
considered in step 9. I believe the results are the same, but it is confusing
and a potential source of error if the two ever get out of sync.

2. But more important, the next step repositions the boxes, based on the
current position value. This has a number of unfortunate effects:
* If the author knows where the caption should be positioned, and that position
is neither centered nor against the left or right edge, it is very difficult to
calculate what value to set for position so that the adjustment yields the
desired location.
* For align:middle captions, it is impossible to position the cue anyplace but
centered in the viewport, since the adjustment will always move the 50%
position of the box to the 50% position of the viewport. So no centering
captions in the left half of the viewport, for instance.
* Captions that are positioned against either edge are not repositioned. Since
this is a common case, the repositioning often isn't noticed or needed at all.

Changing line position from line number to percentage should not have this
effect on the text position. I request that when snap-to-lines is not set, the
values of x and y be used as computed, without adjustment, then repositioned to
address any overlaps.

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Received on Monday, 1 October 2012 21:51:26 UTC