[core] Disable letter-spacing for Arabic labels (issue #9057)

src/mbgl/layout/symbol_layout.cpp

@@ -242,7 +242,7 @@ void SymbolLayout::prepare(const GlyphPositionMap& glyphs, const IconMap& icons)
                         /* horizontalAlign */ horizontalAlign,
                         /* verticalAlign */ verticalAlign,
                         /* justify */ justify,
-                        /* spacing: ems */ layout.get<TextLetterSpacing>() * oneEm,
+                        /* spacing: ems */ util::i18n::allowsLetterSpacing(*feature.text) ? layout.get<TextLetterSpacing>() * oneEm : 0.0f,
                         /* translate */ Point<float>(layout.evaluate<TextOffset>(zoom, feature)[0] * oneEm, layout.evaluate<TextOffset>(zoom, feature)[1] * oneEm),
                         /* verticalHeight */ oneEm,
                         /* writingMode */ writingMode,

src/mbgl/util/i18n.cpp

@@ -1,5 +1,6 @@
 #include "i18n.hpp"
 
+#include <algorithm>
 #include <map>
 
 namespace {
@@ -29,14 +30,14 @@ DEFINE_IS_IN_UNICODE_BLOCK(Latin1Supplement, 0x0080, 0x00FF)
 // DEFINE_IS_IN_UNICODE_BLOCK(CyrillicSupplement, 0x0500, 0x052F)
 // DEFINE_IS_IN_UNICODE_BLOCK(Armenian, 0x0530, 0x058F)
 // DEFINE_IS_IN_UNICODE_BLOCK(Hebrew, 0x0590, 0x05FF)
-// DEFINE_IS_IN_UNICODE_BLOCK(Arabic, 0x0600, 0x06FF)
+DEFINE_IS_IN_UNICODE_BLOCK(Arabic, 0x0600, 0x06FF)
 // DEFINE_IS_IN_UNICODE_BLOCK(Syriac, 0x0700, 0x074F)
-// DEFINE_IS_IN_UNICODE_BLOCK(ArabicSupplement, 0x0750, 0x077F)
+DEFINE_IS_IN_UNICODE_BLOCK(ArabicSupplement, 0x0750, 0x077F)
 // DEFINE_IS_IN_UNICODE_BLOCK(Thaana, 0x0780, 0x07BF)
 // DEFINE_IS_IN_UNICODE_BLOCK(NKo, 0x07C0, 0x07FF)
 // DEFINE_IS_IN_UNICODE_BLOCK(Samaritan, 0x0800, 0x083F)
 // DEFINE_IS_IN_UNICODE_BLOCK(Mandaic, 0x0840, 0x085F)
-// DEFINE_IS_IN_UNICODE_BLOCK(ArabicExtendedA, 0x08A0, 0x08FF)
+DEFINE_IS_IN_UNICODE_BLOCK(ArabicExtendedA, 0x08A0, 0x08FF)
 // DEFINE_IS_IN_UNICODE_BLOCK(Devanagari, 0x0900, 0x097F)
 // DEFINE_IS_IN_UNICODE_BLOCK(Bengali, 0x0980, 0x09FF)
 // DEFINE_IS_IN_UNICODE_BLOCK(Gurmukhi, 0x0A00, 0x0A7F)
@@ -169,13 +170,13 @@ DEFINE_IS_IN_UNICODE_BLOCK(HangulJamoExtendedB, 0xD7B0, 0xD7FF)
 DEFINE_IS_IN_UNICODE_BLOCK(PrivateUseArea, 0xE000, 0xF8FF)
 DEFINE_IS_IN_UNICODE_BLOCK(CJKCompatibilityIdeographs, 0xF900, 0xFAFF)
 // DEFINE_IS_IN_UNICODE_BLOCK(AlphabeticPresentationForms, 0xFB00, 0xFB4F)
-// DEFINE_IS_IN_UNICODE_BLOCK(ArabicPresentationFormsA, 0xFB50, 0xFDFF)
+DEFINE_IS_IN_UNICODE_BLOCK(ArabicPresentationFormsA, 0xFB50, 0xFDFF)
 // DEFINE_IS_IN_UNICODE_BLOCK(VariationSelectors, 0xFE00, 0xFE0F)
 DEFINE_IS_IN_UNICODE_BLOCK(VerticalForms, 0xFE10, 0xFE1F)
 // DEFINE_IS_IN_UNICODE_BLOCK(CombiningHalfMarks, 0xFE20, 0xFE2F)
 DEFINE_IS_IN_UNICODE_BLOCK(CJKCompatibilityForms, 0xFE30, 0xFE4F)
 DEFINE_IS_IN_UNICODE_BLOCK(SmallFormVariants, 0xFE50, 0xFE6F)
-// DEFINE_IS_IN_UNICODE_BLOCK(ArabicPresentationFormsB, 0xFE70, 0xFEFF)
+DEFINE_IS_IN_UNICODE_BLOCK(ArabicPresentationFormsB, 0xFE70, 0xFEFF)
 DEFINE_IS_IN_UNICODE_BLOCK(HalfwidthandFullwidthForms, 0xFF00, 0xFFEF)
 // DEFINE_IS_IN_UNICODE_BLOCK(Specials, 0xFFF0, 0xFFFF)
 // DEFINE_IS_IN_UNICODE_BLOCK(LinearBSyllabary, 0x10000, 0x1007F)
@@ -332,6 +333,14 @@ bool allowsWordBreaking(char16_t chr) {
             || chr == 0x2013 /* en dash */);
 }
 
+bool charAllowsLetterSpacing(char16_t chr) {
+    return !(isInArabic(chr) || isInArabicSupplement(chr) || isInArabicExtendedA(chr) || isInArabicPresentationFormsA(chr) || isInArabicPresentationFormsB(chr));
+}
+
+bool allowsLetterSpacing(const std::u16string& string) {
+    return std::all_of(string.begin(), string.end(), charAllowsLetterSpacing);
+}
+
 bool allowsIdeographicBreaking(const std::u16string& string) {
     for (char16_t chr : string) {
         if (!allowsIdeographicBreaking(chr)) {

src/mbgl/util/i18n.hpp

@@ -10,6 +10,10 @@ namespace i18n {
     by the given Unicode codepoint due to word breaking. */
 bool allowsWordBreaking(char16_t chr);
 
+/** Returns whether the given string can be displayed with letter-spacing.
+    False for Arabic scripts, where letter-spacing will break ligatures. */
+bool allowsLetterSpacing(const std::u16string& string);
+
 /** Returns whether a line break can be inserted after any character in the
     given string. If false, line breaking should occur on word boundaries
     instead. */