Apply Arabic contextual forms natively #3
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If a grapheme cluster begins with a combining diacritical mark or ends with an invisible stacker, combine it with an adjacent grapheme cluster to avoid drawing diacritics over dotted circles or placeholder diacritics where adjacent characters should be ligated instead.
Added a script that fetches the latest Unicode character database’s property file for Indic syllable categories and generates a function for combining graphemes based on it.
Replace zero-width joiners with temporary strip markers to prevent ICU from stripping them.
Preemptively swap combining marks with the characters they modify to visual order, so that the RTL plugin will swap them back to logical order.
Replaced custom word break heuristics when determining line breaks with a word segmenter. Added a simple polyfill for older versions of Firefox.
Fixed an issue where vertical CJK text was shifted upwards by one em.
Stop using mapbox-gl-rtl-text for Arabic character shaping. Instead, use kashida/tatweel to force TinySDF’s canvas to draw Arabic forms in all three contextual forms as well as the isolated form.
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In both SVG and HTML, we can simply wrap each kashida/tatweel character in a span that has a transparent text color, but unfortunately that isn’t possible with the canvas API.
Maybe TinySDF could have a separate mode for Arabic text that builds an SVG, loads it in an |
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Stop using mapbox-gl-rtl-text for Arabic character shaping. Instead, use kashida/tatweel to force TinySDF’s canvas to draw Arabic forms in all three contextual forms as well as the isolated form.
Unfortunately, the extra kashidas/tatweels overstrike upon surrounding glyphs, making it look like the text is haphazardly crossed out. The bitmap that comes out of TinySDF needs to be cropped to just the character of interest, or kashidas/tatweels need to be excluded if the form does not exist for the given letter.
If this works, it would go halfway towards removing the mapbox-gl-rtl-text dependency, which is cumbersome and requires a CDN: maplibre#3215 mapbox/mapbox-gl-js#4007. (bidi-js can likely address the other half, bidirectional text processing.)
Depends on #1.