Advanced text layout

[pointlessone]

Right now (2.4.0 and all versions before) Prawn implements a very simple text layout. It basically renders individual code points. The code points are used as they are present in the input string. This works kinda OK for Latin-based alphabets and hieroglyphic alphabets that don't use any fancy font techniques but doesn't work at all for more complex scripts.

• Hindi fonts not rendered correctly  #830: Hindi seem to actively use glyph substitutions based on the context
• Arabic Support Problem #921: Arabic uses different glyphs depending on where the "letter" is (start, middle, or end of the word), requires glyph substitutions
• Invalid breaks in words with accents #1098: This is not exactly an issue with the advanced fonts features but it's an issue with our basic text segmentation algorithm and maybe how we measure widths of individual code points instead of composite "characters"
• Problem with NFD normalized Unicode #1154: Even European script require feature that are currently beyond Prawn
• Language subscripts not working properly for Khmer #1170: Khmer requires advanced glyph positioning and substitution
• Thai double diacritics are not correctly rendered #1126: another example of Thai requiring more advanced text layout
• Myanmar font is not being rendered correctly #1125: This script also extensively uses glyph substitution

There are no issues for this but this basic font rendering also prevents use of ligatures or contextual alternatives provided by fonts.

---

This issue is a canonical explantation for the lack of support of certain scripts. Community is welcome to work on a more advanced text layout.

[jyxjjj]

I didn't understand, For example, will JetBrians Mono no ligatures? or with ligatures?
There was no ligature settings, should i open a new issue?

[pointlessone]

@jyxjjj I believe the font does have ligatures but Prawn doesn't support ligatures. You can open a new issue but I'm not planning to work on anything like it in the near future. I will gladly accept a contribution though.