> From: Egmont Koblinger <[email protected]> > Date: Thu, 31 Jan 2019 10:11:22 +0100 > Cc: [email protected] > > > It doesn't do _any_ shaping. Complex script shaping is left to the > > terminal, because it's impossible to do shaping in any reasonable way > > [...] > > Partially, you are right. On the other hand, as far as I know, shaping > should take into account the neighboring glyphs even if those are not > visible (e.g. overflow from the viewport), and the terminal is unaware > of what those glyps are. This is an area that "presentation form" > characters can address for Arabic – although as it was pointed out, > not for Syrian and some others.
Arabic presentation forms are more like an exception than a rule, I hope you understand this by now. Most languages/scripts don't have such forms, and even for Arabic they cover only a part of what needs to be done to present correctly shaped text. Complex script shaping is much more than just substituting some glyphs with others, it requires an intimate knowledge of the font being used and its capabilities, and the ability to control how various glyphs of a grapheme cluster are placed relative to one another, something that an application running on a text terminal cannot do. So I suggest that you don't consider Arabic presentation forms a representative of the direction in which terminal emulators supporting such scripts should evolve.
