[HarfBuzz] Zero-width joiner has width

[Simon Cozens]

On 08/08/2015 15:25, Behdad Esfahbod wrote:
>> Ok, that makes sense. And yes, I was ignoring the advance for glyphs and instead using Freetype to return the glyph width. I think I stole that bit of code from xetex. :-)
> 
> Really?

It may not be totally true. I don't know if XeTeX ignores the advance
data - it probably doesn't - but I certainly stole the glyph bounds
measurement code from XeTeXFontInst::getGlyphBounds.

However, when I replace SILE's glyph width measurement code with
'glyph_pos[j].x_advance / 64.0' instead of getting the glyph advance out
of Freetype, I get slightly different output.

With Harfbuzz's x_advance, a Gentium letter "m" at 10pt measures as
8.03125pt wide; using the width information from Freetype, I get
8.0322265625pt. I can't account for the discrepancy and I don't know who
is right.

S