1230497 - Core Text shaping failure in Indic text due to join-control characters

Status: RESOLVED FIXED

(Core :: Graphics: Text, defect)

Description

[Jonathan Kew [:jfkthame]]

Spun off from bug 1194105 comment 6, as I think this is distinct from the original issue in that bug.

Testcase:

  data:text/html;charset=utf-8,
    <span style="font:36px Telugu MN">&%23xc15;&%23xc4d;&%23x200c;

should render the same as:

  data:text/html;charset=utf-8,
    <span style="font:36px Telugu MN">&%23xc15;&%23xc4d;

i.e. the ZWNJ should not affect it. But it fails, because Telugu MN doesn't include glyphs for ZWNJ/ZWJ, and this causes Core Text to use a fallback (even though it won't be visible). This then makes us think shaping failed, and punt to harfbuzz, which can't actually shape this (AAT-only) font properly.

Comment 1

[Jonathan Kew [:jfkthame]]

Attachment: Ignore font fallback in Core Text shaping if it's just for a join-control character

Comment 2

[Jonathan Kew [:jfkthame]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/803db6db0f680e066a2e3830cdd22959b07a0459
Bug 1230497 - Ignore font fallback in Core Text shaping if it's just for a join-control character. r=jdaggett

Comment 3

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/803db6db0f68