[HarfBuzz] behavior of mark-width-zeroing

[Jonathan Kew]

On 10/6/14 03:05, Martin Hosken wrote:
> Dear Jonathan,
>
>> Our current mark-zeroing code, in zero_mark_widths_by_gdef() and
>> zero_mark_widths_by_unicode(), modifies only the advance of the glyphs,
>> so that they no longer take up any space on the line.
>>
>> I'm wondering whether we should also adjust the offset, by subtracting
>> the advance from it before we zero the advance. (Though perhaps only if
>> there's no GPOS positioning?)
>
> How would that affect anchor positioning? Would the offset be ignored or would one need to subtract the advance from all the anchors too?

This is part of the heuristics to try and make legacy fonts that lack 
real layout tables behave acceptably. So I'd suggest we only do this if 
the font does not include actual GPOS positioning rules. If it does, 
then we trust them.

JK