1179073 - Text "Spın̈al Tap" renders correctly (diaeresis on "n") in most cases, but as "Spınäl Tap" (diaeresis on "a") when using courier new, e.g. in view source

Status: NEW

(Core :: Graphics: Text, defect)

Description

[Andy Goth]

Attachment: screenshot.png

User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Firefox/38.0
Build ID: 20150525141253

Steps to reproduce:

Access http://www.fossil-scm.org/index.html/info/6cd7087a35cb8448
Search for "inappropriate"
See "Spın̈al Tap" in the browser, which is good
View page source
Search for "inappropriate"
See "Spınäl Tap" in the page source window, which is bad

Additional note: As shown in the screenshot, the problem appears to be misplaced combining characters or some such.  Notice how when searching for "al Tap", said characters are highlighted white-on-green, but the diaeresis is NOT shown in white.


Actual results:

Saw "Spınäl Tap" in page source window


Expected results:

Should have seen "Spın̈al Tap" in page source window

Comment 1

[Andy Goth]

Clearly the problem also shows up in any <pre> tags!  See above for a demonstration.  Or maybe the problem is with any fixed-width font, or with fonts requiring characters to be synthesized, or some such.  I don't know how any of this is implemented, so I'm just guessing.

Look very closely at the bug title (shown in the page title and header line, right under the bug number, to see correct rendering.

Comment 2

[Andy Goth]

Additional research was done by Martijn Coppoolse.  See email here:
http://www.mail-archive.com/[e-mail]/msg20922.html

Martijn demonstrated the problem is specifically tied to Courier New and that rendering is correct for other fonts.

I tried showing n-diaeresis in Courier New in different editors/viewers and got varying results.  Thunderbird has the same problem, Notepad shows the diaeresis floating in space between the n and the a, and Vim renders it correctly (!).  So it's possible to show n-diaeresis in Courier New in Windows 7.

My follow-up email:
http://www.mail-archive.com/[e-mail]/msg20925.html

Comment 3

[Andy Goth]

Attachment: rendering in Notepad and Vim

Comment 4

[:Gijs (he/him)]

Jonathan, this seems like something you'd be interested in?

(fwiw, I can repro on my win8 machine on which I'm looking at this bugreport)

Comment 5

[Jonathan Kew [:jfkthame]]

Given comment 2, it seems pretty clear this is the result of a defect in the Courier New font.

FWIW, I can reproduce the same behavior with Courier New on Mac OS X in both Firefox and Chrome, although Safari manages to put the dieresis over the 'n'. In IE10 on Windows, I see "Spın¨al" with a spacing dieresis. The variability of the results between different applications is a clue that the font may not be well engineered, and its results depend on how the rendering system deals with poorly-specified edge cases.

A possible workaround is to use a different monospaced font that doesn't suffer from this defect: e.g. Consolas on Windows, or Courier on OS X, etc.