2013/4/20 Behdad Esfahbod <[email protected]> > Konstantin has brought up a few interesting issues regarding variation > selectors. I'll summarize issues that I think can be improved: > > - Right now we don't handle a sequence of multiple variation selectors > in a > row. What *is* the best way to handle that? Ideally the extra ones should > become visible. Even a box is better than silently not showing them, > right? >
http://unicode.org/faq/unsup_char.html says unhandled variation selectors shouldn't be visible. Even more, all variation selectors are of default_ignorable property and expected to be rendered as completely invisible, when unhandled. I'd say we shouldn't make them visible unless HB_BUFFER_FLAG_PRESERVE_DEFAULT_IGNORABLES, and that is what we currently have. However, I don't like the way HB currently makes them invisible - by removing them from the output glyph array. > - Now, Unicode says only registered variation sequences are valid. I > assume > we don't want to enforce that? > You forgot to mention using the variation selectors in Ideographic Variation Database, too. I don't think we should enforce sequences validation; this could be implemented in user's get_glyph() (or get_glyph_variation()), if user really wants that. > - What should HB_BUFFER_FLAG_PRESERVE_DEFAULT_IGNORABLES do to variation > selectors? Right now they do not become visible no matter what. Is it > relevant whether the variation selector was actually used during glyph > lookup > or not? > If we're going to not eat the variation selectors from the output, then they would pass through the path the other default_ignorable-s do, thus guaranteeing consistency. > - If the answer to the last question of the previous item is yes, then we > would new to change get_glyph() API to two separate get_glyph_variation() > and > get_glyph() calls. But that would be an API and ABI break :(. Thinking > about > it now, I wish I had done that from the beginning. > > > Thoughts? > > -- > behdad > http://behdad.org/ > _______________________________________________ > HarfBuzz mailing list > [email protected] > http://lists.freedesktop.org/mailman/listinfo/harfbuzz > Regards, Konstantin
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