On the correct positioning of the anchors

mauro sacchetto

As per title. For example I place an anchor on top of |O| and an anchor at the base by gravecomb. Now, there is a good practice or a custom thanks to which are the anchors at the right height? Also, the two anchors of the example it is advisable that both (base and mark) are placed at the same height, thus changing the position of the comb glyph if necessary, or they can be placed at different heights?
Thank you
m

John Hudson

All the relationships between anchors and outlines and heights are entirely arbitrary, because the only thing that matters is that the anchors will be aligned when applied. That said, there are some common practices, although these vary depending on the script and the number of anchors involved.

In a Latin font, it is quite common for above mark anchors on bases to be vertically aligned to or near the tops of letters, e.g. at the x-height and cap-height, and for below mark anchors to be aligned to or near the baseline. Then the corresponding anchors on the mark glyphs are set at appropriate distances below/above the mark outline to achieve the desired positioning in composites or in GPOS output.

It is also common in Latin fonts for the marks outlines to be aligned to each other at a default height, and optically positioned horizontally at the same location relative to the zero-width, such that all their anchors can be in the same location in the glyph space.

John Hudson

Some scripts require more anchors than others, due to the variety of marks involved and their interactions. In that case, it can be helpful to avoid situations where anchors are stacked on top of one another, to make it easier to select individual anchors, so I will sometimes vertically position the anchors on bases 10 unit increments, and the corresponding anchors on the marks at -10 unit incremements.

mauro sacchetto

Ok, I set all I think correctly. Thank you!