Add bidirectional (RTL) text support

[abaye123]

Closes #184 (RTL/Hebrew/Arabic rendering).

Summary

Adds proper right-to-left text rendering to pdfmake. Implements the visible parts of the Unicode Bidi Algorithm (UAX#9) at the line level, leaning on fontkit (already part of pdfkit) for the per-text-call glyph reversal that it does well, and filling in the parts fontkit can't see across multiple text() calls.

No changes required in pdfkit — the fix is entirely in pdfmake.

What works

• rtl: true on any text/table/list node (or in defaultStyle).
• Auto-bidi for mixed paragraphs even without rtl: true (Hebrew embedded in English etc.).
• Default alignment becomes right when rtl: true and no explicit alignment is set.
• Bracket mirroring per UAX#9 L4 ((שלום) renders with the brackets pointing the right way for a Hebrew reader).
• Currency symbols (₪, €, £, $, ¥, ¢ and U+20A0–U+20CF) treated as ET so '₪3.50' renders as a single LTR group inside RTL text — currency sign visually to the left of the amount.
• Tables: rtl: true reverses column order, with correct colSpan handling.
• Lists: rtl: true puts bullets/numbers on the right edge.
• Margins: [left, top, right, bottom] mirrors to [right, top, left, bottom] in RTL.
• Justify: last line of a justify paragraph in RTL snaps to the right edge instead of the left.

How it works

• src/helpers/bidi.js (new) — minimal UAX#9 implementation: bidi class detection, paragraph direction (P2/P3), W1–W7, N1/N2, I1/I2, L1, L2, L4 (bracket mirroring).
• src/helpers/bidi.js applyBidiToLine() — segments a line's inlines by (sourceInline, bidiLevel, isStrongRTL), applies L2 visual reordering, mirrors brackets in odd-level segments, manually reverses neutral-only RTL segments (that fontkit otherwise leaves in logical order), swaps leadingCut/trailingCut to match fontkit's runtime char reversal.
• LayoutBuilder.buildNextLine calls applyBidiToLine after the line is built but before it's added to the page.
• DocMeasure.measureTable reverses the column order when rtl is in effect, walking left-to-right in the original row and writing right-to-left in the new row so colSpan descriptors land at the correct (leftmost) slot of their visual span block.
• LayoutBuilder.processList reserves the marker gap on the right (vs. left) when rtl is set, and pins the marker to the right end of its block to keep the visible bullet-to-text gap symmetric with LTR.
• ElementWriter.alignLine recognizes the RTL last-line case for justify.
• helpers/node.js getNodeMargin mirrors [left, top, right, bottom] when rtl is in effect.

Test plan

• npm run lint clean
• npm run mocha — 419 unit tests pass (37 new for bidi/RTL: 32 in tests/unit/helpers/bidi.spec.js, 5 in tests/unit/DocMeasure.spec.js)
• npm run build:node — clean Babel output
• Visual regression via examples/rtl_hebrew.js — 10 sections covering pure RTL, mixed bidi, embedded English/digits, alignment, bold/large styling, multi-line wrapping, RTL table with prices, ordered/bullet lists, brackets and quotes, justify

Known limitations (out of scope)

• Arabic letter shaping (joining/contextual forms) — needs HarfBuzz; out of scope. Hebrew works fully.
• Explicit bidi embedding controls (LRE/RLE/PDF/LRI/RLI/FSI/PDI) — implicit ordering only.

Sample

examples/rtl_hebrew.js produces examples/pdfs/rtl_hebrew.pdf. Run:

node examples/rtl_hebrew.js

(Uses Arial from C:\Windows\Fonts because Roboto has no Hebrew glyphs.)

[abaye123]

Hi @liborm85, thanks for the consideration! Pushed a fix for the CI failures (amended into the original commit):

• Download Hebrew font on demand in the example so the build doesn't need it committed
• Suppress the URL warning in bidi.js
• Renamed ot → [new name] to satisfy the typos check

CI should be green now. Ready to test when you get a chance 🙏

[abaye123]

Hi @liborm85 Is there any prospect of a merger?