LibGfx: Implement TrimmedTable mappings for Cmaps

Author: https://github.com/janso3
Commit: https://github.com/SerenityOS/serenity/commit/5b7dfe848d
Pull-request: https://github.com/SerenityOS/serenity/pull/16932

Userland/Libraries/LibGfx/Font/OpenType/Cmap.cpp

@@ -83,6 +83,8 @@ u32 Cmap::Subtable::glyph_id_for_code_point(u32 code_point) const
         return glyph_id_for_code_point_table_0(code_point);
     case Format::SegmentToDelta:
         return glyph_id_for_code_point_table_4(code_point);
+    case Format::TrimmedTable:
+        return glyph_id_for_code_point_table_6(code_point);
     case Format::SegmentedCoverage:
         return glyph_id_for_code_point_table_12(code_point);
     default:
@@ -129,6 +131,20 @@ u32 Cmap::Subtable::glyph_id_for_code_point_table_4(u32 code_point) const
     return (be_u16(m_slice.offset_pointer(glyph_offset)) + delta) & 0xffff;
 }
 
+u32 Cmap::Subtable::glyph_id_for_code_point_table_6(u32 code_point) const
+{
+    u32 first_code = be_u16(m_slice.offset_pointer((u32)Table6Offsets::FirstCode));
+    if (code_point < first_code)
+        return 0;
+
+    u32 entry_count = be_u16(m_slice.offset_pointer((u32)Table6Offsets::EntryCount));
+    u32 code_offset = code_point - first_code;
+    if (code_offset > entry_count)
+        return 0;
+
+    return be_u16(m_slice.offset_pointer((u32)Table6Offsets::GlyphIdArray + code_offset * 2));
+}
+
 u32 Cmap::Subtable::glyph_id_for_code_point_table_12(u32 code_point) const
 {
     u32 num_groups = be_u32(m_slice.offset_pointer((u32)Table12Offsets::NumGroups));

Userland/Libraries/LibGfx/Font/OpenType/Cmap.h

@@ -67,6 +67,11 @@ public:
             Constant = 16,
             NonConstMultiplier = 4,
         };
+        enum class Table6Offsets {
+            FirstCode = 6,
+            EntryCount = 8,
+            GlyphIdArray = 10
+        };
         enum class Table12Offsets {
             NumGroups = 12,
             Record_StartCode = 16,
@@ -80,6 +85,7 @@ public:
 
         u32 glyph_id_for_code_point_table_0(u32 code_point) const;
         u32 glyph_id_for_code_point_table_4(u32 code_point) const;
+        u32 glyph_id_for_code_point_table_6(u32 code_point) const;
         u32 glyph_id_for_code_point_table_12(u32 code_point) const;
 
         ReadonlyBytes m_slice;