[HarfBuzz] No kerning?

[Behdad Esfahbod]

My guess is that you are truncating advances as returned by HarfBuzz whereas
perhaps you need to round them.  That explains 99% of issues like the ones you
are seeing...

On 15-10-12 12:17 PM, Jamie Dale wrote:
> I've continued to investigate this, and it seems to be related to my call
> to hb_font_set_scale. The value I was passing was a float multiplier for the
> font (you can see it being used in my first email) - I've tried changing that
> to use the up-scaled value that we give to FT_Set_Transform, however I'm still
> getting different results to what HarfBuzz itself calculates from FreeType[1].
> 
> If I omit my call to hb_font_set_scale (which I can do now that it's set
> correctly by HarfBuzz), then the layout of the text changes considerably. The
> particular issue I highlighted before is fixed, however a lot of the other
> text scrunches up to an almost illegible level. This is also true if I use the
> HarfBuzz FT font directly (rather than go through my own font caching -
> although this was to be expected since my caching should never change the raw
> values returned from FreeType).
> 
> Below is the screenshot when I'm calling hb_font_set_scale:
> Inline images 1
> 
> Below is the screenshot when I omit the call to hb_font_set_scale:
> Inline images 2
> 
> Note that the "r" characters scrunch up against the other characters to become
> almost illegible. This is most noticeable in smaller text, large text looks fine.
> 
> I'm going to try this in the sample app I was using before, so I can see if
> it's somehow related to the rest of our font rendering pipeline.
> 
> [1] The reason I'm seeing a different result is that the FreeType font lists
> its scale as 24,576, and then HarfBuzz calculates its internal scale as 768.
> Given that I gave FT_Set_Transform a scale of (1.0f * 65536) I'm not exactly
> sure where FreeType gets that scale from, but regardless, I ultimately end up
> zeroing the scale that the HarfBuzz font is using :(