Proposal for BiDi in terminal emulators

[Egmont Koblinger via Unicode]

Hi Eli,

> Does anyone know of a terminal emulator which supports isolates?

GNOME Terminal's (VTE's) current work-in-progress implementation does
remember BiDi control characters just like it remembers combining
accents, that is, tied to the preceding letter's cell. It uses FriBidi
1.0 for the BiDi work, so yes, it supports Unicode 6.3's isolates.

There's one significant issue, though. Because we currently just
misuse our existing infrastructure of combining accents for the BiDi
controls, BiDi controls at the very beginning of a paragraph are
dropped. Addressing this issue would need core changes to the terminal
emulation behavior, such as introducing in-between-cells storage, or
zero-width special characters belonging to a cell _before_ the cell's
actual letter, or something like this. I outline one idea in my
specification, but it's subject to discussion to finalize it.

(There's also a less significant issue: copy-pasting fragments of text
probably doesn't produce the contents that make the most sense wrt.
BiDi controls. I'm not sure what other software do here, though.)

Mintty is also actively working on BiDi support, I believe its author
just recently added support for isolates. It uses its own BiDi
implementation.


cheers,
egmont