Hello,
I tried to use the XAdvance for the second glyph, and I get the red line as showed in the picture.
So is there an explanation for this?
When you click the Help button, as advised, the user manual opens at OpenType Designer - Pair Adjustment and explains it:
Note: Even though you can set values for the second glyph, it is recommended that you keep those values all at zero. If you do set any of those values to non-zero, the text layout engine will skip the next possible pair for adjustment, which is usually not what a font designer intends, or expects to happen.
It is also explained in the GPOS section of the OpenType font specification:
During text processing, a client applies a lookup to each glyph in the string before moving to the next lookup. A lookup is finished for a glyph after the client locates the target glyph or glyph context and performs a positioning action, if specified. To move to the “next” glyph, the client will skip all the glyphs that participated in the lookup operation: glyphs that were positioned as well as any other glyphs that formed an input sequence context for the operation. Only glyphs in the input sequence are skipped; in the case of chained contexts positioning, the glyphs in the lookahead sequence are not skipped.
There is just one exception: the “next” glyph in a sequence may be one of those that formed a context for the operation just performed. Specifically, in the case of pair positioning operations (i.e., kerning), if the ValueRecord for the second glyph is null, that glyph is treated as the “next” glyph in the sequence.
So if you leave it this way, any possible kerning between the Second glyph and the next glyph is ignored. If you do not want to ignore it, just set XAdvance for the Second glyph to zero and put the value 200 in both XAdvance and XPlacement for the First glyph.
Ok, noted and understood. Thanks