[HarfBuzz] improving hb_ot_hide_default_ignorables

[Jonathan Kew]

On 27/9/13 16:26, Shriramana Sharma wrote:
> On Fri, Sep 27, 2013 at 8:52 PM, Jonathan Kew <jfkthame at googlemail.com> wrote:
>>
>> ...except in the (unlikely) case where the font does not actually support
>> the <space> character. This will be almost vanishingly rare, of course - but
>> unfortunately it happens with the "MarkA" font that's used for a variety of
>> rendering tests.
>
> Sorry if this is a stupid question but why don't you just add the
> space glyph to that font? I mean, it's not as if you actually have to
> draw any glyph! You mention that the patch will impact performance. In
> which case, trying to support a font without a space glyph doesn't
> seem as good justification, no?
>

The patch won't hurt performance for fonts that *do* have a glyph for space.

Sure, for the particular case of the test font that resulted in a 
failure, we could modify the font and ignore the issue.

But it's also conceivable - not likely, but possible - that the 
situation will arise with other fonts. Not fonts intended for normal 
text, obviously, but perhaps icon/emoji/private-use fonts that are only 
expected to support a specific collection of symbols.

So IMO we might as well make harfbuzz "robust" against this particular 
edge case, given that we can easily do so without impacting any other usage.

JK