1128658 - HarfBuzz Multiple substitution does NOT delete glyph: Font rendering Issue Arial Unicode MS

Status: RESOLVED FIXED

(Core :: Layout: Text and Fonts, defect)

Description

[Tom Hindle]

Attachment: fontrenderingbug.html

User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:35.0) Gecko/20100101 Firefox/35.0
Build ID: 20150122214805

Steps to reproduce:

When the following string is rendered using "Arial Unicode MS"

किंतान 

(\u0915\u093F\u0902\u0924\u093E\u0928)






Actual results:

Its displaying two 'dots' instead of a single 'dot'


Expected results:

It should display a single dot.

IE - displays a single dot.
Chrome - displays the same behavior as Firefox.

Comment 1

[Tom Hindle]

Attachment: ActualFirefox.png

Comment 2

[Tom Hindle]

Attachment: ExpectedIE.png

Comment 3

[Jonathan Kew [:jfkthame]]

This appears to be a harfbuzz issue; cc'ing Behdad. I can reproduce with a standalone hb-view or hb-shape tool.

Example sequence, using Arial Unicode 1.01x:

  U+0915,U+093F,U+0902

In this example, the 'abvs' feature in Arial Unicode wants to replace the short-i matra with a form that includes the anusvara dot at an appropriate position, and delete the original anusvara glyph. But we fail to apply the second of these substitution lookups, and so the original no-longer-wanted anusvara remains.

Comment 4

[Behdad Esfahbod]

(In reply to Jonathan Kew (:jfkthame) [PTO, back March 2nd] from comment #3)
> This appears to be a harfbuzz issue; ...
> ...
> ...and delete the original anusvara glyph. But we fail to apply the
> second of these substitution lookups, and so the original no-longer-wanted
> anusvara remains.

Correct.  I was aware that Uniscribe allows a MultipleSubst to have zero output glyphs (essentially allowing deleting a glyph completely) but we disallow that.  Allowing it is trivial except that I need to figure out what to do with its cluster values.  Perhaps merging with previous glyph is enough.  If there's no previous, then with following.  Jonathan, what do you think?

Comment 5

[Behdad Esfahbod]

Note that OpenType spec specifically makes deletion using MultipleSubst *illegal*.  But the Microsoft implementation does not follow that apparently.

Comment 6

[Krasnaya Ploshchad’]

HarfBuzz now allowing MultipleSubst to delete glyph in 1.3.0, this bug can be fixed.

Comment 7

[Jonathan Kew [:jfkthame]]

Resolving as fixed (by harfbuzz updates in recent months).