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w3c / ttml2

Timed Text Markup Language 2 (TTML2)
https://w3c.github.io/ttml2/
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Application semantics of font selection strategy. #1082

Closed skynavga closed 5 years ago

skynavga commented 5 years ago

Clarify that application semantics of the font selection strategy property applies to glyph areas, which may take into account more or less character context to determine that selection according to the value of the property.

nigelmegitt commented 5 years ago

In my view this is an unnecessary and possibly unhelpful change. It could be misleading, because the font selection strategy affects the layout of lines, particularly when tts:lineHeight="normal".

My reasoning is that tts:lineHeight applies to p elements, and the algorithm used to compute the used value when the specified value is normal requires knowledge of the actual font used, which could be affected by the font selection strategy.

If we normatively restrict the application of fontSelectionStrategy to glyph areas, that could be interpreted as a signal that no knowledge of fontSelectionStrategy is needed except when drawing glyphs, which is not the case.

I'd prefer to close this with no change.

skynavga commented 5 years ago

Your logic does not hold, since tts:fontFamily says

The tts:fontFamily attribute is used to specify a style property that defines the font family from which glyphs are selected for glyph areas generated by content flowed into a region.

and since tts:fontSelectionStrategy is merely a parameter for the algorithm used to resolve tts:fontFamily.

Therefore, adding the phrase to glyph areas is entirely consistent with the language in tts:fontFamily, and, further, the lack of this phrase makes it inconsistent with the latter.

nigelmegitt commented 5 years ago

I've raised #1102 to clarify that fontSelectionStrategy is in fact used in calculating the used value of line height when tts:lineHeight="normal". Assuming that we include the proposed changes in that issue, then I have no problem with making the changes in this issue.