Crate gpui_bidi 

Bidirectional-text index↔x mapping for gpui shaped lines.

Why this exists

The platform shapers already do bidi correctly. Shape "سلام دنیا" and the glyphs come back in visual order carrying logical byte indices — for that string, indices 15, 13, 11, 9, 8, 6, 2, 0 as x ascends. That is exactly what UAX #9 asks for, and it means RTL text renders right today.

What is wrong is how those glyphs get read back. gpui’s LineLayout::x_for_index returns the first glyph whose index >= target, which assumes byte index and x rise together. In an RTL line the first glyph carries the highest index, so every offset in the line resolves to the same glyph and the caret collapses onto x = 0. index_for_x and closest_index_for_x fail the same way, and mixed content is worse: in "hello سلام world" the four offsets 6, 8, 10, 12 all map to one x.

So this crate is mostly not an implementation of the bidi algorithm — the shaper did that, and this reads its already-reordered glyph table correctly. The one thing the glyph table cannot tell you is a glyph’s embedding LEVEL: at the edge of an embedded run the glyph beside it belongs to the other run and carries a misleading index, so direction inferred from geometry is wrong exactly there. Those levels come from unicode-bidi, given the text — see VisualMap::with_levels.

Shape of the API

VisualMap is built from plain (logical byte index, x) pairs, so every rule here is unit-testable without a window, a GPU, or a font. Hosts get those pairs from a shaped line — see VisualMap::from_glyphs and the gpui adapter in shaped.

What a caller still owns

• Paragraph direction (which side a line starts on) is the host’s, from the first strong character. This crate only maps within a shaped line.
• Logical caret movement. Left/right arrows moving in logical order needs nothing from here. For the visual movement platforms actually do in bidi text, see VisualMap::step_visual.

Modules

paragraph

Logical-order line breaking for right-to-left paragraphs.

shaped

The gpui adapter: read a VisualMap out of a shaped line.

Structs

Glyph

One glyph as this crate needs it: where it came from in the source, and where it was laid out.

VisualMap

A shaped line’s glyphs, indexed so logical offsets and visual positions can be converted in both directions regardless of writing direction.