On Wed, Jan 30, 2019 at 05:56:00PM +0200, Eli Zaretskii via Unicode wrote: > > - It doesn't do Arabic shaping. > > 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 > without controlling the fonts being used and accessing the font > information, and this is not possible when you run on a terminal
It's the inverse of the situation with RTL reordering. The interface between the program and the terminal is a character cell grid (really, a sequence of printables and \e-based codes, but that's a technical detail). The program (emacs in this case) can do arbitrary reordering of characters on the grid, it also has lots of information the terminal doesn't. For example, what are you going to do when there's a line longer than what fits on the screen? Emacs will cut and hide part of it; any attempts to reorder that paragraph by the terminal are outright broken as you don't _have_ the paragraph. Same for a popup window on the middle of the screen partially obscuring some text underneath. And if you argue "so make emacs print your new code to disable formatting", so do thousands of other programs that are less sophisticated than emacs. On the other hand, all that the program can output is a sequence of Unicode codepoints. These don't include shaping information, and are not supposed to. The shaping is explicitly meant to be done by the terminal, and it's the terminal who's equipped with _most_ of the needed data (it might lack context just outside screen's end or under an overlapped window, but that's not specific to complex shaping -- same can happen for the other half of a CJK character). You know if the font used supports shaping, you can have access to a graphic view (as opposed to the array of codepoints) -- heck, it's only you who know the text is rendered on a screen rather than a Braille device. And if you miss an opportunity to shape something, the result is still readable to the user, merely not as good as it could be. Meow! -- ⢀⣴⠾⠻⢶⣦⠀ ⣾⠁⢠⠒⠀⣿⡁ Remember, the S in "IoT" stands for Security, while P stands ⢿⡄⠘⠷⠚⠋⠀ for Privacy. ⠈⠳⣄⠀⠀⠀⠀
