Merge pull request #477 from SixLabors/js/fix-474

Fix ligature caret offset determination

Author: JimBobSquarePants

src/SixLabors.Fonts/Tables/AdvancedTypographic/GlyphDefinitionTable.cs

@@ -125,8 +125,8 @@ public static GlyphDefinitionTable Load(BigEndianBinaryReader reader)
 
         ushort glyphClassDefOffset = reader.ReadUInt16();
         ushort attachListOffset = reader.ReadUInt16();
-        ushort ligatureCaretListOffset = reader.ReadUInt16();
-        ushort markAttachClassDefOffset = reader.ReadUInt16();
+        ushort ligatureCaretListOffset = reader.ReadOffset16();
+        ushort markAttachClassDefOffset = reader.ReadOffset16();
         ushort markGlyphSetsDefOffset = 0;
         uint itemVarStoreOffset = 0;
 

src/SixLabors.Fonts/Tables/AdvancedTypographic/LigatureCaretList.cs

@@ -22,22 +22,22 @@ public static LigatureCaretList Load(BigEndianBinaryReader reader, long offset)
         // ----------|--------------------------------|--------------------------------------------------------------------------------------------------------
         reader.Seek(offset, SeekOrigin.Begin);
 
-        ushort coverageOffset = reader.ReadUInt16();
+        ushort coverageOffset = reader.ReadOffset16();
         ushort ligGlyphCount = reader.ReadUInt16();
 
         using Buffer<ushort> ligGlyphOffsetsBuffer = new(ligGlyphCount);
         Span<ushort> ligGlyphOffsets = ligGlyphOffsetsBuffer.GetSpan();
         reader.ReadUInt16Array(ligGlyphOffsets);
 
-        var ligatureCaretList = new LigatureCaretList()
+        LigatureCaretList ligatureCaretList = new()
         {
-            CoverageTable = CoverageTable.Load(reader, offset + coverageOffset)
+            CoverageTable = CoverageTable.Load(reader, offset + coverageOffset),
+            LigatureGlyphs = new LigatureGlyph[ligGlyphCount]
         };
 
-        ligatureCaretList.LigatureGlyphs = new LigatureGlyph[ligGlyphCount];
         for (int i = 0; i < ligatureCaretList.LigatureGlyphs.Length; i++)
         {
-            ligatureCaretList.LigatureGlyphs[i] = LigatureGlyph.Load(reader, ligGlyphOffsets[i]);
+            ligatureCaretList.LigatureGlyphs[i] = LigatureGlyph.Load(reader, offset + ligGlyphOffsets[i]);
         }
 
         return ligatureCaretList;

src/SixLabors.Fonts/Tables/AdvancedTypographic/LigatureGlyph.cs

@@ -12,11 +12,9 @@ public static LigatureGlyph Load(BigEndianBinaryReader reader, long offset)
         reader.Seek(offset, SeekOrigin.Begin);
 
         ushort caretCount = reader.ReadUInt16();
-        var ligatureGlyph = new LigatureGlyph()
+        return new LigatureGlyph()
         {
             CaretValueOffsets = reader.ReadUInt16Array(caretCount)
         };
-
-        return ligatureGlyph;
     }
 }

tests/Images/ReferenceOutput/Test_Issue_474-.png

@@ -0,0 +1,30 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Text;
+
+namespace SixLabors.Fonts.Tests.Issues;
+
+public class Issues_474
+{
+    [Fact]
+    public void Test_Issue_474()
+    {
+        StringBuilder stringBuilder = new();
+        stringBuilder.AppendLine("Latin: The quick brown fox jumps over the lazy dog.");
+        string text = stringBuilder.ToString();
+
+        FontCollection fontCollection = new();
+        string serviceNow = fontCollection.Add(TestFonts.ServiceNowWoff2).Name;
+
+        FontFamily mainFontFamily = fontCollection.Get(serviceNow);
+        Font mainFont = mainFontFamily.CreateFont(30, FontStyle.Regular);
+
+        // There are too many metrics to validate here so we just ensure no exceptions are thrown
+        // and the rendering looks correct by inspecting the snapshot.
+        TextLayoutTestUtilities.TestLayout(
+            text,
+            new TextOptions(mainFont),
+            includeGeometry: false);
+    }
+}

tests/SixLabors.Fonts.Tests/Fonts/ServiceNow-Sans-Text-Bold-unmastered-1.1.woff

@@ -291,6 +291,8 @@ public static class TestFonts
 
     public static string SofiaSansCondensedLight => GetFullPath("SofiaSansCondensed-ExtraLight-Regular.ttf");
 
+    public static string ServiceNowWoff2 => GetFullPath("ServiceNow-Sans-Text-Bold-unmastered-1.1.woff");
+
     public static Stream TwemojiMozillaData() => OpenStream(TwemojiMozillaFile);
 
     public static Stream SegoeuiEmojiData() => OpenStream(SegoeuiEmojiFile);