589862 - [harfbuzz] overlapping glyphs with diacritics in monospaced fonts

Status: RESOLVED FIXED

(Core :: Graphics, defect)

Description

[Jonathan Kew [:jfkthame]]

(Also posted to harfbuzz mailing list.)

Monospaced fonts such as DejaVu Sans Mono and Consolas (Win7) render incorrectly when combining diacritics are used; the following glyph overprints the base+diacritic combination. This causes the wordwrap-03 reftest to fail under harfbuzz on Win7.

Simple testcase:
data:text/html,<div style="font-family:consolas,monospace">foobar<br/>fo&#xf3;bar<br/>foo&#x301;bar

On Win7 with gfx.font_rendering.harfbuzz.level=1, the third line will show the problem.

Comment 1

[Jonathan Kew [:jfkthame]]

Attachment: screenshot showing overlapping glyphs from the testcase

Comment 2

[Jonathan Kew [:jfkthame]]

Attachment: patch, v1 - don't override advances in mark-to-base attachment

(As posted to the harfbuzz mailing list.)

Comment 3

[Jonathan Kew [:jfkthame]]

Requesting blocking-2.0 as this prevents us enabling harfbuzz by default on windows, due to reftest failures.

Comment 4

[John Daggett (:jtd)]

Comment on attachment 468373 [details] [diff] [review]
patch, v1 - don't override advances in mark-to-base attachment

Looks good.  Probably want a reftest for this.

Comment 5

[Jonathan Kew [:jfkthame]]

http://hg.mozilla.org/mozilla-central/rev/459aab9180b9

The wordwrap-03 reftest already catches this on Windows when we enable harfbuzz, as it uses combining diacritics in monospace. The first patch in bug 590101 will cause it to catch this issue on OS X as well, because it will hit the harfbuzz text path instead of coretext there as well. So we're sufficiently covered, I think.