[HarfBuzz] optimization for ASCII-only text

[Jonathan Kew]

On 9/8/12 19:21, Behdad Esfahbod wrote:
> Hi Jonathan,
>
> Thanks for bringing this up.  And more profiling is hugely appreciated.
>
> I like to take it to a different direction though: if text is all 
> ASCII and
> all glyphs are in the font, then the normalization pass should really boil
> down to a cmap lookup for each glyph.  In which case we should be able to
> combine it with hb_map_glyphs() to make one cmap lookup per character 
> instead
> of current too.  That should make the normalizer overhead go away.  
> Indeed, if
> you check in the profile, all time spent in the normalizer is in 
> HBGetGlyph,
> and is equal to time spent in hb_substitute_default.
Right, it's the cmap lookup that costs the time here (and if we can make 
our GetGlyph callback faster, that'd help too). So if map_glyphs can be 
combined with the check that normalization is doing, that should be 
equally effective. Maybe not quite as trivial to implement, but by all 
means, go for it! :)

>
> Easy fish would be hb_set_unicode_props.  Maybe I make that lazy.  
> Don't know.
>   We need some of that stuff after mapping to glyphs, so we need to be 
> able to
> predict whether we would ever need to look at them...  Or make it faster.
>
> Makes sense?
>
> behdad