978313 - ZWJ is breaking next character

Status: RESOLVED FIXED

(Core :: Graphics: Text, defect)

Description

[ebrahim]

Attachment: Screenshot.png

User Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:30.0) Gecko/20100101 Firefox/30.0 (Beta/Release)
Build ID: 20140225040206

Steps to reproduce:

data:text/html;charset=utf8,‍یت


Actual results:

The result I see is "ی‌ت"


Expected results:

It should be like "یت", just like Chrome (see the attached screenshot)

Comment 1

[Jonathan Kew [:jfkthame]]

Huh, that's weird. I see the same problem on OS X; it's not specific to a particular platform or font.

It only seems to affect text at the beginning of the line:

data:text/html;charset=utf8,&zwj;یت &zwj;یت &zwj;یت<br>&zwj;یت &zwj;یت

This makes me wonder if it's somehow related to bidi processing; cc'ing smontagu.

Comment 2

[Jonathan Kew [:jfkthame]]

Attachment: initialize matchType appropriately for run-initial control chars that default to the primary font.

This is a bit of an edge case: the issue here is caused by matchType not being set correctly in the case where we find a run-initial control char and hence use the default initial value from prevFont. We can fix this by initializing it correctly to kFontGroup, and thus avoiding a break in the glyph run.

Comment 3

[Jonathan Kew [:jfkthame]]

Attachment: reftest for initial ZWJ disrupting Arabic joining.

Comment 4

[Jonathan Kew [:jfkthame]]

Attachment: initialize matchType appropriately for run-initial control chars that default to the primary font.

Updated to handle the issue that b2g and some android versions have an Arabic font that doesn't explicitly support ZWJ - this was resulting in a font change, but we should avoid that in order to maintain expected shaping behavior. We don't need the ZWJ character to be present in the font, as harfbuzz handles it appropriately.

Comment 5

[Jonathan Kew [:jfkthame]]

Attachment: reftest for initial ZWJ disrupting Arabic joining.

Comment 6

[Jonathan Kew [:jfkthame]]

Attachment: fix up existing reftests affected by improved joiner handling.

Fix up a couple of issues where existing tests were (inadvertently) depending on the absence of joiners in a font, resulting in glyph run boundaries and shaping interruption.

Comment 7

[Jonathan Kew [:jfkthame]]

Try run with these patches: https://tbpl.mozilla.org/?tree=Try&rev=13f7f324f0bf

Comment 8

[Jonathan Kew [:jfkthame]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/d30141d69df1
https://hg.mozilla.org/integration/mozilla-inbound/rev/169b77523fe6
https://hg.mozilla.org/integration/mozilla-inbound/rev/9af980ae7109

Comment 9

[Ed Morley [:emorley]]

https://hg.mozilla.org/mozilla-central/rev/d30141d69df1
https://hg.mozilla.org/mozilla-central/rev/169b77523fe6
https://hg.mozilla.org/mozilla-central/rev/9af980ae7109