Re: Pango crossplatform layout size query

[Behdad Esfahbod <behdad behdad org>]

On 04/08/2010 03:45 PM, Richard Procter wrote:
> 
> On 9/04/2010, at 4:49 AM, Behdad Esfahbod wrote:
> 
>> On 04/06/2010 08:09 PM, Richard Procter wrote:
>>> However, the cairo documentation states "hinting font metrics means
>>> quantizing them so that they are integer values in
>>> device space". This
>>> suggests I'm wrong and that layout remains device dependent.
>>
>> ??  If you *disable* hinting font metrics, you are supposed to get
>> device-independent layout.
> 
> Right, that's what I thought.
> 
> "quantizing ... so that they are integer values in device space" though
> suggests otherwise to me; I will go bug the cairo guys.

I don't understand.  I *am* cairo guys :).

If metrics hinting is ON, then quantization happens -> device-dependent.
If metrics hinting is OFF, no quantization -> device-independent.


>>> I have tested this using the attached C program on OS X 10.4,
>>> Debian Linux (lenny), and Win32, using the same MS arial.ttf font file.
>>> OS X and Linux get identical logical extents, but win32 differs (see
>>> below for details - in fact it doesn't appear to honour the option).
>>
>> IIRC neither win32 nor quartz cairo font backends respect the hinting
>> flags (yet).  That's a bug.
> 
> It looks like quartz has been fixed - it matches linux with metrics
> hinting off and differs with it on.

Nope.  Quartz one doesn't respect the flags either.  Just happens that Apple
doesn't quantize, while Microsoft does.


> I will raise a bug for the win32 backend if there isn't one already.

It's fairly known issue.  No one to fix it though.


>>> If I understand metrics hinting, this last is a bug, and I can rely
>>> on the others to remain equal, plus or minus a pixel? If so, can
>>> I expect this to hold for other scripts?
>>
>> Yes.  The script is not relevant.
> 
> Great. I take it that I am basically on the right track then and that
> when you said cross-platform results without metrics hinting were
> 'fairly robust' you were thinking of that single device pixel.

More or less.

behdad


> many thanks,
> Richard.