528454 - ligature is visually split when it crosses the beginning of a relatively positioned element

Status: NEW

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

Description

[Robin Whittleton]

User-Agent:       Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.2b2) Gecko/20091108 Firefox/3.6b2
Build Identifier: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.2b2) Gecko/20091108 Firefox/3.6b2

Ligatures occur across element boundaries (good) but don’t decompose with potentially breaking style changes (bad).

Reproducible: Always

Steps to Reproduce:
1. Load testcase
Actual Results:  
Part of the 'f' character is shifted down, part remains at original height.

Expected Results:  
Decomposed the ligature and then shifted the 'f' down intact.

Testcase requires Zapfino font, couldn’t think of a crossplatform font with obvious ligatures.

Comment 1

[Robin Whittleton]

Attachment: Testcase demoing original bug (requires Zapfino font)

Comment 2

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

I think we don't want to decompose at element boundaries in general; that's a feature and not a bug.

However, I think we probably should be doing so for the relative positioning boundary.  (Though that does break the invariant that relative positioning just moves the existing element.)

Comment 3

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Right, I really didn't want to break that invariant.

Is there a real-world use-case for this that isn't adequately served by just turning off ligatures (e.g., using letter-spacing:0.1px or a future font-variant extension)?

Comment 4

[Robin Whittleton]

My original testcase for this was wondering if you could do an Amiga-intro style bouncing text animation using js. So no, not really real-world ;) If you can force ligature decomposition using letterspacing and it's going to be a pain to fix this then it's probably a WONTFIX

Comment 5

[Robert O'Callahan (:roc) (email my personal email if necessary)]

I'll let David make that call.