RE: Default rendering of Combining diacritical marks

From: Peter Constable (
Date: Wed Mar 08 2006 - 19:30:06 CST

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    I believe that Vista beta 1 has the updated fonts, though they are probably not the final versions.


    One could also say that XP users would benefit if all of the new features of Vista were made available on XP. :-)


    The placement of the dot below on the left of the 'h' is simply the default overstrike positioning of that mark; GDI isn't doing anything to try to position it other than drawing the outline where the font designer put it.


    As I mentioned, existing users of XP can get correct positioning if they use appropriate fonts. This takes a little more explaining than "it just works", but it takes time to get everything to "just work". With Vista, we will largely have reached that point for this set of users.







    From: saqqara []
    Sent: Wednesday, March 08, 2006 6:21 AM
    Cc: Peter Constable
    Subject: Re: Default rendering of Combining diacritical marks


    Thank you for the information on WIndows Vista. Is this all present in the upcoming Beta? Obviously, it would be useful for XP users is the core fonts updates were to be available for XP, Microsoft Office users at some point.


    I was aware of the Opentype features needed for the most satisfactory presentation of marks. But just to give a more explicit description:


    If I select "Times New Roman" and output (using the low level API TextOutW) an 'h' followed by COMBINING DOT BELOW, the dot is placed below the baseline but to the left of the character cell rather than at the centre as expected. GDI has tried to do some default handling for the mark but for some reason chosen this odd place to put the dot. Windows 2000 appears to be the same as XP here. After feedback here, I remain of the view that if it were my code, I'd want to correct the problem to avoid unexpected behaviour with legacy fonts! Oh well, GDI is 23 years old now so I guess it should know what its doing - I still remember when it was such a cute newborn!


    Incidentally this came up as I'm writing a piece on Egyptian Transliteration in Unicode (although the problem also comes up in Arabic transliteration in Latin script so not actually as obscure as it sounds). Ideally I want end users to have minimal ifs and buts. Sounds like the best practical solution for casual use is just to accept the misplaced dot for now knowing it will eventually go away - for neater appearance for publication in short term, one can fiddle about with specialist fonts (as I do personally at the moment).





            ----- Original Message -----

            From: Peter Constable <>

            To: saqqara <> ;

            Sent: Tuesday, March 07, 2006 6:53 AM

            Subject: RE: Default rendering of Combining diacritical marks


            Strictly speaking, it is not a bug but rather a limitation in functionality - not a supported feature in that version. In fact, the functionality is supported in part.


            You need three things for such combinations to display correctly: (1) OpenType fonts with special tables needed to support mark positioning, (2) support in the platform for Latin combining marks, and (3) applications that support Latin combining marks. Windows XP/SP2 includes the second item, and at least some of the apps that ship with Windows XP/SP2 (e.g. Notepad, Wordpad, IE) meet the bar for item 3. What's missing is item 1: the fonts that ship with XP/SP2 do not have the tables needed to position combining marks.


            All of the Windows core fonts that will ship with Windows Vista have been updated to include support for combining marks as well as full Unicode 4.1 Latin character coverage (and Greek, etc. - all the fonts that the core fonts already support are updated to 4.1). There are also third-party fonts you can use on XP/SP2 to support combining marks, such as the Doulos and Charis fonts from SIL.






            From: [] On Behalf Of saqqara
            Sent: Monday, March 06, 2006 3:20 AM
            Subject: Default rendering of Combining diacritical marks


            Windows XP/SP2. When I use COMBINING DOT BELOW with an OpenType font without specific support for the combination (e.g. current release of Times New Roman for most diacritic latin forms) the dot is placed to the bottom left of the character box rather than the centre (e.g. try d or D with the combining dot).


            Am I correct in categorising this as a Windows text rendering bug or am I missing a more subtle point about how Unicode software is expected to deal with this situation?



            Bob Richmond



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