fcft_kerning - calculate kerning distance between two wide characters
fcft_kerning() calculates the kerning distances x (horizontal) and y (vertical) between the two wide characters left and right, in pixels.
Both characters must exist in the primary font.
fcft_kerning() is just a convenience function around FT_Get_Kerning() and as such, it only supports legacy kern tables. In particular, OpenType fonts' GPOS tables are not supported. fcft is not a text shaping library.
On success, fcft_kerning() returns true, and x and y are updated with the kerning distance, in pixels.
On error, false is returned. This may happen for several reasons: