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feat: Arabic/Farsi/Urdu bidi reordering and contextual shaping — PR 1/3 (#2541)

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Co-authored-by: Uri Tauber <uritaube@gmail.com>
This commit is contained in:
Husam Younis
2026-07-13 16:02:21 +03:00
committed by GitHub
co-authored by Uri Tauber
parent 552b2683e6
commit 932a472835
18 changed files with 1087 additions and 62 deletions
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lib/MiniBidi/minibidi.h
+52 -5
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@@ -5,8 +5,10 @@
* minibidi.h — standalone header for ESP32C3 BiDi calculations
*
* Derived from [mintty](https://github.com/mintty/mintty/) (Thomas Wolff, MIT licence).
* Stripped of: Arabic shaping, box-drawing mirror, terminal dependencies,
* GCC nested functions, VLAs, and non-Hebrew/English Unicode data.
* Includes: UAX#9 bidi (do_bidi) and Arabic contextual shaping (do_shape),
* both ported from mintty src/minibidi.c (Ahmad Khalifa, Thomas Wolff).
* Stripped of: box-drawing mirror, terminal dependencies, GCC nested
* functions, VLAs, and Unicode data for scripts CrossPoint doesn't render.
*/
#include <stdbool.h>
@@ -34,13 +36,18 @@ typedef uint32_t ucschar; /* Unicode codepoint; BMP-only content fits uint16_t
#define BIDI_MAX_LINE 128
/* ── bidi_char ───────────────────────────────────────────────────────── */
/* origwc: the codepoint as it came from the epub text stream
wc: working codepoint (may be replaced by mirrored form after do_bidi)
index: original logical position, so the caller can reorder glyphs */
/* origwc: the codepoint as it came from the epub text stream
wc: working codepoint (may be replaced by mirrored form after
do_bidi, or by an Arabic contextual form after do_shape)
index: original logical position, so the caller can reorder glyphs
joiners: ZWJ/ZWNJ context for Arabic shaping, mintty layout:
low nibble = joiners that logically FOLLOW this character,
high nibble = joiners that logically PRECEDE this character */
typedef struct {
ucschar origwc;
ucschar wc;
uint16_t index;
uint8_t joiners;
} bidi_char;
/* ── Bidi character classes (UAX #9) ────────────────────────────────── */
@@ -71,6 +78,20 @@ enum {
PDI, /* Pop Directional Isolate */
};
/* ── Arabic joining formatter flags (bidi_char.joiners nibbles) ─────── */
/* Values match mintty's minibidi.h: ZWNJ 0x01, ZWJ 0x02. do_shape()
compares nibble values directly, so these must not be changed. */
enum {
ZWNJ = 0x01, /* U+200C ZERO WIDTH NON-JOINER */
ZWJ = 0x02, /* U+200D ZERO WIDTH JOINER */
};
/* Sentinel written by do_shape() over the Alef absorbed into a Lam-Alef
ligature. Callers must filter it out when emitting shaped text.
(Upstream mintty writes a space instead — a terminal must keep the cell;
a proportional-text renderer must drop the character entirely.) */
#define LIGATURE_PLACEHOLDER 0xFFFFu
/* ── Public API ──────────────────────────────────────────────────────── */
/*
@@ -94,6 +115,32 @@ bool is_rtl_class(uchar bc);
*/
ucschar mirror(ucschar ch);
/*
* do_shape(line, to, count)
*
* Applies Arabic contextual shaping (and Lam-Alef ligation) to
* `line[0..count-1]`, writing the result to `to[0..count-1]`.
*
* MUST be called AFTER do_bidi(): the algorithm resolves joining from
* VISUAL adjacency (line[i-1] is the visually-left neighbour, line[i+1]
* the visually-right one), exactly like upstream mintty.
*
* line: visual-order input; the joiners field must be populated by the
* caller (in logical order, before do_bidi) for ZWJ/ZWNJ support
* to: output buffer, same size as line; non-Arabic entries are copied
* through unchanged. An Alef absorbed by a Lam-Alef ligature is
* replaced with LIGATURE_PLACEHOLDER — filter it on emission.
* count: number of characters (≤ BIDI_MAX_LINE)
*
* Returns 1.
*
* Ported from mintty src/minibidi.c (Ahmad Khalifa, Thomas Wolff,
* MIT licence), https://github.com/mintty/mintty — with CrossPoint
* extensions for Perso-Arabic letters and in-stream diacritics, see
* minibidi.c for details.
*/
int do_shape(bidi_char* line, bidi_char* to, int count);
/*
* do_bidi(autodir, paragraphLevel, line, count)
*