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Re: [ft-devel] Seams with disjoint composite

From: Behdad Esfahbod
Subject: Re: [ft-devel] Seams with disjoint composite
Date: Thu, 07 Jun 2012 12:48:21 -0400
User-agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv: Gecko/20120306 Thunderbird/3.1.20

BTW, checkout DejaVuSans at 4pt.  I see all kinds of triangular artifacts.

On 06/07/2012 12:40 PM, Behdad Esfahbod wrote:
> On 06/05/2012 01:56 AM, Werner LEMBERG wrote:
>>> I was playing with Unicode box characters, and noticed that DejaVu
>>> Sans creates the glyph for ▟ out of three quadrant boxes.  At
>>> different sizes I can see very noticeable seams where the sub-glyphs
>>> meet.  I thought FreeType would handle these cases better, but seems
>>> like I'm wrong.  Any ideas?  Does FreeType combine all contours
>>> together and rasterize them in one pass, or raster them separately
>>> and combine?
>> They are rasterized in a single pass.  However, the DejaVu font
>> doesn't contain the necessary bytecode to properly handle the rounding
>> issues which inevitably happen if subglyphs are combined -- in ftview,
>> press key `f' to force autohinting, and you won't see seams.  I've
>> just confirmed that exactly the same issue is present with the Windows
>> rasterizer, so it's not a FreeType problem.
> Thanks Werner for looking into this!  Great time for asking then: are subglyph
> positions rounded as part of the hinting process?
> behdad
>> Of course, a much simpler (and probably even better) solution is to
>> avoid subglyphs if they touch at longer lines.
>>     Werner

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