376472 - Zero-width characters rendered incorrectly

Status: RESOLVED FIXED

(Core :: Graphics, defect)

Description

[Philip Taylor]

User-Agent:       Opera/9.10 (Windows NT 5.0; U; en)
Build Identifier: 

Strings that contain zero-width characters, e.g. bug 366643 comment #13, are rendered incorrectly: the zero-width characters are visible (as some random shape depending on what character it is), and the end of the line disappears if you try selecting the first few characters.

The same behaviour occurs on Windows Server 2003 and on Windows 2000.

This worked correctly in:
  Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.9a4pre) Gecko/20070402 Minefield/3.0a4pre
It fails in:
  Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.9a4pre) Gecko/20070403 Minefield/3.0a4pre

Reproducible: Always

Comment 1

[Philip Taylor]

Attachment: incorrect output

The three lines should each look like:
    x.x.x

Comment 2

[Stuart Parmenter]

Attachment: fix1

there are 2 possible fixes here and i'm not sure which one is better.  In the patch I landed that regressed this I fixed checking for missing glyphs in 2 ways.  First was setting displayZWG before calling Shape (which causes this problem, but fixes others) and the second was by using ScriptGetCMap to tell if we're missing glyphs.  

Fortunately the ScriptGetCMap path means we don't actually need to set fDisplayZWG, but we can't use SGCMap with surrogates.  So I guess the question is are there buggy fonts that support surrogates that need the fDisplayZWG workaround or not.  I don't know the answer.  Can anyone find a testcase that uses some surrogate zero width characters?


The other fix is to just remove the fDisplayZWG all together.

Comment 4

[Biju]

I am seeing problem with "Zero-width Joiner(NWJ)"
and  "Zero-width Non-Joiner(NWNJ)" 

Let me know if I should not create another bug.

Example:- 
1. ള്‍ NWJ
2. ള്‌ NWNJ

Comment 6

[Stuart Parmenter]

this should have been fixed by 377950