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bug#7887: Emacs will render some fonts under Mac OS X one pixel too tall

From: Jan Djärv
Subject: bug#7887: Emacs will render some fonts under Mac OS X one pixel too tall (patch supplied)
Date: Sat, 29 Jan 2011 11:39:09 +0100
User-agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; sv-SE; rv: Gecko/20110123 Thunderbird/3.1.8

Anders Lindgren skrev 2011-01-25 18.18:

My original suggesten simply said that anything in the range -2.0 -
-2.0001 should be treated as -2. The motivation behind this is that
often a floating-point error is only in the lowest bit or bits. (In
the case I found, the bits that were set corresponds to the least
significant mantissa bits of a 32 bit floating-point number, even
though the number had been converted to 64 bit number along the way.)

If it only to handle fp errors, then I guess 0.0001 is OK.  Patch checked in.
I don't have any fonts to test with, so if you can confirm that it is fixed, that would be great.


        Jan D.

On Tue, Jan 25, 2011 at 5:12 PM, Jan Djärv <address@hidden> wrote:
> Sounds like a job for round then.
>        Jan D.
> Anders Lindgren skrev 2011-01-25 15.45:
>> No, that won't work. Descents are always negative, "floor" is used to
>> treat, for example, -2.5 as -3.0, to avoid clipping. The problem is
>> that is also converts -2.000001 to -3.
>> What I suggested was that we continue to round -2.5 down to -3, but
>> round values very close to -2.0 up to -2.
>> I don't know if this is a general problem, only related to FontForge
>> (an open-source font editor). If it's only related to FontForge, then
>> another solution would be to fix it instead of Emacs.
>>     -- Anders

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