577380 - Firefox trunk no longer forming ligatures that 3.6 does.

Status: RESOLVED FIXED

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

Description

[Jonathan Kew [:jfkthame]]

+++ This bug was initially created as a clone of Bug #575695 +++

See the URL field. In the "traffic" and "floret" samples at the end, the f-ligatures are not rendered properly unless gfx.font_rendering.harfbuzz.level is reset to 0.

Comment 1

[Jonathan Kew [:jfkthame]]

Attachment: patch, v1 - force Mac font back-end to use Core Text for AAT fonts

This is the patch that was originally posted to bug 575695 (refreshed), to ensure we use the Core Text path for fonts that have AAT tables and do not have OpenType layout tables. Without this, the switch to harfbuzz as the default font rendering backend causes a regression for such fonts.

Comment 2

[Jonathan Kew [:jfkthame]]

Attachment: patch, mac-only reftest for AAT font support

This simply checks that the "fi" ligature is working in Times. On OS X, Times is an AAT font and does not have OpenType tables, so the ligature will only work if we're using the Core Text backend.

Comment 3

[Mike Beltzner [:beltzner, not reading bugmail]]

Moving to betaN - requires beta coverage, no specific beta milestone targetted at this time.

Comment 4

[John Daggett (:jtd)]

Comment on attachment 457817 [details] [diff] [review]
patch, mac-only reftest for AAT font support

The skip-if should be random-if.  According to dbaron, the skip-if is only for cases where a testcase causes a crash, otherwise the additional test on other platforms assures additional testing coverage, even if the test itself will be ignored.

Comment 5

[John Daggett (:jtd)]

Comment on attachment 457816 [details] [diff] [review]
patch, v1 - force Mac font back-end to use Core Text for AAT fonts

The logic seems right (use CoreText when AAT but no OT tables exist).  My only concern would be testing coverage, Apple seems to stick morx/mort tables in lots of the fonts it ships.  Did you iterate over default fonts on 10.5/10.6 and note which ones were affected by this change?

Comment 6

[Jonathan Kew [:jfkthame]]

Pushed patch and reftest:
http://hg.mozilla.org/mozilla-central/rev/0b126c0c5744

(In reply to comment #5)
> Comment on attachment 457816 [details] [diff] [review]
> patch, v1 - force Mac font back-end to use Core Text for AAT fonts
> 
> The logic seems right (use CoreText when AAT but no OT tables exist).  My only
> concern would be testing coverage, Apple seems to stick morx/mort tables in
> lots of the fonts it ships.  Did you iterate over default fonts on 10.5/10.6
> and note which ones were affected by this change?

I didn't specifically iterate, but I know it will affect most default fonts shipped on OS X, and so it will substantially reduce testing coverage for the harfbuzz backend until we get it enabled by default on Windows. That's the main reason I didn't include this logic in the initial harfbuzz landing, but we need to do it now as FF4 approaches.

Now that this has landed, most of our current harfbuzz coverage will be from downloadable fonts, which are hardly ever AAT-only.