The Unicode Standard does define the rendering of such combinations, which
is in the absence of any other information to stack outwards.
Implementations that can't do that will either overstrike, or use some other
A sophisticated rendering will use positioning such as control point
matching to get optimal positioning. A dumb implementation would simply move
the accent outwards if there was in the same position. This will not
necessarily produce an optimal positioning, but should be readable.
It may take a non-trivial amount of code to do the former (especially if it
means adding control point hinting, as in TrueType). If it take megabytes of
code to do the latter there is probably something else wrong.
----- Original Message -----
From: "Antoine Leca" <Antoine.Leca@renault.fr>
To: "Unicode List" <email@example.com>
Sent: Monday, November 13, 2000 10:11
Subject: Re: Devanagari question
> Marco Cimarosti wrote:
> > Antoine Leca wrote:
> > > My understanding is that there are a number of similar cases,
> > > which are not
> > > officially prohibited (AFAIK), but does not carry any sense.
> > I think that the original idea behind having combining marks in Unicode
> > that *any* combination of base + diacritic should be permitted,
> The fact that it is permitted (as I said, they "are not prohibited")
> does not per se give them any sense...
> This was my point, but I was not clear enough.
> > and be handled decently by rendering engines.
> The question here is the meaning of "decently".
> I beg your pardon, but as the programmer of a rendering engine, I cannot
> agree that I should spend hours and days, and furthermore adding megabytes
> of code, to render "decently" combinations like digits + accents (by
> decently, I mean I should check if the glyph for the digit have ascender
> above x-height, or being of narrower width, and then adjust the position
> the diacritic accordingly; similarly, adjusting the descender position of
> Nagari virama according to the descender depth of a preceding "g" or "j"
> At the contrary, I believe that when a combination is not expected, the
> renderer should have a very basic and straightforward behaviour, and just
> "print" the default glyphs in order, with overstriking when the second
> is a combining mark. Doing something more complex, in addition to be IMHO
> a complete lost of time for both the programmer and the users (to load
> code), is also likely to give some users the idea that using some weird
> combinations are handled this ("clever") way everywhere, thus leading to
> when the datas will be brought elsewhere.
> > If font designers and d. engines implementers insist in the idea that an
> > "accented letter" may be rendered only if an ad-hoc glyph has been
> > anticipated in the font, many minority languages will never have a
> > being supported at a reasonable cost.
> I never say (nor I hope I implied) such an idea.
> Now, insisting that any renderer should align properly any diacritic on
> top (or bottom) middle of the I, M and W glyph, will have for net result
> that nobody will never be able to create any renderer...
> > Less common combinations, used in less known languages, may get along
> > less-than-perfect rendering -- but *no* rendering at all is not
> Where anyone stated such an idea?
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