Harfbuzzy

[elcritch]

Summary

Adds an optional Harfbuzzy-backed text shaping path while keeping Pixie as the default text backend. The branch moves FigDraw text layout toward glyph-id-first rendering, adds source-range and caret mapping helpers for shaped text, and includes a Windy demo for Arabic/Hebrew shaping using bundled OFL Noto fonts.

Changes

• Adds figdrawTextBackend compile-time backend selection:
  • pixie remains the default.
  • hybrid uses Harfbuzzy layout with Pixie-compatible rasterization.
  • harfbuzzy uses Harfbuzzy shaping plus glyph-id rasterization.
• Adds backend-neutral glyph layout data:
  • FontGlyphId
  • GlyphSourceRange
  • ArrangedGlyph
  • GlyphArrangement.sourceRunes
  • GlyphArrangement.arrangedGlyphs
• Adds source mapping and caret APIs:
  • glyph/source range lookup by rune or byte range
  • selection rects by source range
  • point-to-glyph/source hit testing
  • source insertion index caret positions
• Splits text backend logic into Pixie and Harfbuzzy adapters.
• Adds Harfbuzzy shaping support for:
  • shaped glyph ids
  • cluster/source mapping
  • wrapping at shaped glyph boundaries
  • CJK/Kana/Hangul adjacent wrapping
  • combining marks
  • mixed LTR/RTL runs
  • Arabic and Hebrew marks
• Adds glyph-id rasterization through HarfBuzz draw callbacks.
• Updates glyph cache identity to use fontId + glyphId.
• Adds docs in docs/font_shaping.md.
• Adds examples/windy_text_shaping_demo.nim, defaulted to Harfbuzzy via examples/windy_text_shaping_demo.nims.
• Bundles OFL-licensed Noto Naskh Arabic and Noto Sans Hebrew fonts for the demo.

Testing

Ran:

• nim r -d:figdrawTextBackend=harfbuzzy tests/tfontutils.nim
• nim r -d:figdrawTextBackend=hybrid tests/tfontutils.nim
• nim r tests/tfontutils.nim
• nim test
• nim r -d:figdraw.runOnce examples/windy_text_shaping_demo.nim

Also verified the demo sidecar .nims loads and reports backend=harfbuzzy.

Notes

The Harfbuzzy integration is compile-time gated and does not expose HarfBuzz handles through FigDraw’s public node APIs. Pixie remains the default backend.