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Status: Available
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Cc:
behdad@chromium.org
kojii@chromium.org
e...@chromium.org
drott@chromium.org
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Pri: 3
Type: Feature



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Use harfbuzz cluster level 1 to allow coloring marks in different colors

Project Member Reported by kojii@chromium.org, Nov 15 
@khaledhosny said Firefox uses level 1 to color combining marks in different colors.

https://github.com/w3c/csswg-drafts/issues/699#issuecomment-438985815

https://bugzilla.mozilla.org/show_bug.cgi?id=729993

The patch seems as simple as adding:
> hb_buffer_set_cluster_level(buffer, HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS);

Need to learn a bit more what it does and its impact.

Comment 1 by drott@chromium.org, Nov 15 

It's not as simple as it changes how HarfBuzz returns cluster information and character indices. In my understanding, just adding that would break our grapheme fallback logic including the Emoji cluster grouping that we just recently fixed in  issue 774302 .

Comment 2 by kojii@chromium.org, Nov 16 

Good point, I suspected there will be impacts but was not sure what they are.

Font fallback is very like affected, thank you!

Comment 3 by behdad@google.com, Nov 16 

We've talked about this before.  Maybe we can extend cluster models to a new one that will contain information of both level 0 and level 1.
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