I am trying to develop a coptic in Unicode. I already have the gylphs in a font file but there are specific marks that are placed on the top left of the letters (sometimes the middle) which would be easy to recreate if it preceded the letter. But in the Unicode standard, all marks must be written after the letter. So the only thing I can do is use OpenType to always move those marks to the desired position on the letter.
I have used Microsoft Volt to try this but the final font file still didn't look correct when I install it in an OS and try to use it.
Any recommendations of other ways of developing the font in Opentype?