Howdy, Stranger!
Categories
- All Categories
- 39 Introductions
- 3.6K Typeface Design
- 764 Font Technology
- 1K Technique and Theory
- 587 Type Business
- 435 Type Design Critiques
- 526 Type Design Software
- 30 Punchcutting
- 132 Lettering and Calligraphy
- 79 Technique and Theory
- 53 Lettering Critiques
- 461 Typography
- 289 History of Typography
- 111 Education
- 61 Resources
- 479 Announcements
- 74 Events
- 104 Job Postings
- 147 Type Releases
- 153 Miscellaneous News
- 259 About TypeDrawers
- 52 TypeDrawers Announcements
- 109 Suggestions and Bug Reports
Options
How to avoid Latin mark to letters combination fallback to legacy codepoints?
aminabedi68
Posts: 7
Hello
I'm developing a new version of a typeface which has a wide Latin character support in both ways:
legacy registered codepoints (like: U+00E0=à)
opentype mark to combine marks and base letters (like: U+0061=a and U+0300=gravecomb)
I started to test both ways inside browsers and apps, and realized that mark and base letters fallback to legacy codepoints! The font has no problem but I don't know if all things is correct in my tests or not, I'm looking for a CSS property or browser flag to disable the fallback. Have you ever face this problem? What is your solution?
Tagged:
0
Comments
1. Unicode NFC normalisation, which maps from decomposed sequences to precomposed characters at the text level (NFD normalisation maps the other way). Normalisation may be applied to the stored text or in a buffered layer between the stored text and the displayed text, e.g. as part of sorting or searching operations.
2. Text layout engine font interacton, mapping from decomposed to precomposed when selecting which glyph(s) to paint at the font cmap level. I think this was originally implemented in layout engines in the interests of downstream processing efficiency, and to avoid broken diacritics in the days before reliable mark-to-base positioning, but it means that font makers are burdened with the legacy requirement to include precomposed glyphs for those diacritics that have Unicode encodings.
There’s basically nothing that font makers can do about this. Even if text is normalised to decomposed strings using NFD, layout engines may still map to the precomposed glyphs at the cmap level. If you want your fonts to always display the decomposed glyph sequences, then you actually have to decompose them at the glyph level in the font ccmp feature, e.g.
agrave -> a gravecomb
AFAIK there isn’t a way to disable that. Which is to say, many layout engines choose to combine mark and base, if the combined thing is supported in the font. Unicode says they are canonically equivalent, and the layout engine might reasonably think the layout should be at least as good and possibly better, so….
I will share what I have done, even though I imagine there are some better solutions.
One thing you can do instead is test your base characters and anchors via combinations that do NOT in fact have precombined codepoints.
That is, test the anchoring point on the “a” by testing it in combination with diacritic characters with which “a” has no precombined form supported in your font.
Similarly, test the anchor point on the acute diacritic by testing it in combination with letters with which it has no precombined form supported in your font.