Mark to Base on Ligatured glyphs

WAY KYI

I have ligatured glyphs ( above base ) and I want to adjust the kerning by Mark ( ligatured glyph ) to Base ( Base Glyph ). In the first case, I want to adjust the ligatured glyph at the middle of base glyph. In a second case I want to adjust ligatured glyph to the right edge of the post base glyph. I tried with Mark to Base and that did not seem to work ( I put the first glyph as base and ligatured glyph as Mark ). Unless I create two ligatured glyphs ( using different position ) and call upon the right one with back/match/ahead lookup. My question is - ligatured glyph does not act on mark to Base no matter you switch the mark/base to ligatured glyph, Why is that? Second question is what is the best way to adjust them without  adding same ligatured glyphs? Thanks

Simon Cozens

The way I handle this is to put two anchors on the bases and switch between two mark-to-base lookups contextually.

WAY KYI

Mr. Simon Cozens, thank you very much for your suggestion. Sorry, I was a bit busy with other things. Do you mean, I use GSUB ( Contextual Substitution ) feature to call GPOS ( Mark to Base )? I haven't done like this before, so I may need a little sample if you have one. Thanks

John Hudson

Do you mean, I use GSUB ( Contextual Substitution ) feature to call GPOS ( Mark to Base )?

No, contextual GPOS. Mark anchor positioning lookups are inherently substitutive: the mark ends up on the last anchor that is specified in the lookups, so you can have a default anchor—where the mark is located in most situations—but also one or more additional anchors on each base to which the mark will move in particular contexts. The context rules work similarly to how they do in GSUB, but instead of performing glyph substitutions they are effectively performing anchor subsitutions, saying ‘In this context, use this anchor instead of the previous anchor’.