I am working to modify an existing font (Sacramento, under SIL OFL license), and wish to adjust kernings after having made a few stylistic changes.
I thought I had found the proper way to do it (modifying the existing kerning by class lookup table), but there is some inconsistencies between what is shown in the kerning lookup definition dialog and what is shown in the metrics window when I try out the font.
Here is an example with a "S" glyph followed by a "t" (note that both these glyphs have been modified compared to the original font I have based my new font on):
Kerning data (sorry for french dialog):
In the first case, the horizontal bar of the "t" clearly starts from under the loop of the "S", whereas in the metrics view, the "t" is located further aways from the "S".
When I generate the font and actually try it in a software, it seems the result is closer to what is shown in the kerning defintion dialog:
What could cause this inconsistency? Are there some parameters the Metrics view doesn't take into account? As shown below, when I go in the dropdown at the top of the Metrics view to select the kerning lookup table, the "kerning by class" lookup table is grayed out (there are two other existing kerning per glyph tables that are not grayed out). Why?