Fix #470 , cover #468

Author: JimBobSquarePants

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

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using static SixLabors.Fonts.Tables.AdvancedTypographic.CoverageFormat2Table;
+
 namespace SixLabors.Fonts.Tables.AdvancedTypographic;
 
 /// <summary>
@@ -23,7 +25,10 @@ public static CoverageTable Load(BigEndianBinaryReader reader, long offset)
         {
             1 => CoverageFormat1Table.Load(reader),
             2 => CoverageFormat2Table.Load(reader),
-            _ => throw new InvalidFontFileException($"Invalid value for 'coverageFormat' {coverageFormat}. Should be '1' or '2'.")
+
+            // Harfbuzz (Coverage.hh) treats this as an empty table and does not throw.
+            // SofiaSans Condensed can trigger this. See https://github.com/SixLabors/Fonts/issues/470
+            _ => new EmptyCoverageTable()
         };
     }
 
@@ -124,4 +129,9 @@ public static CoverageFormat2Table Load(BigEndianBinaryReader reader)
 
         return new CoverageFormat2Table(records);
     }
+
+    internal sealed class EmptyCoverageTable : CoverageTable
+    {
+        public override int CoverageIndexOf(ushort glyphId) => -1;
+    }
 }

src/SixLabors.Fonts/Tables/AdvancedTypographic/GPos/AnchorTable.cs

@@ -11,7 +11,7 @@ namespace SixLabors.Fonts.Tables.AdvancedTypographic.GPos;
 [DebuggerDisplay("X: {XCoordinate}, Y: {YCoordinate}")]
 internal abstract class AnchorTable
 {
-    private static readonly AnchorTable Empty = new EmptyAnchor();
+    private static readonly AnchorTable EmptyAnchorTable = new EmptyAnchor();
 
     /// <summary>
     /// Initializes a new instance of the <see cref="AnchorTable"/> class.
@@ -53,9 +53,9 @@ public static AnchorTable Load(BigEndianBinaryReader reader, long offset)
             2 => AnchorFormat2.Load(reader),
             3 => AnchorFormat3.Load(reader),
 
-            // Harfbuzz (Anchor.hh) and FontKit appear to treat this as a default anchor and do not throw.
+            // Harfbuzz (Anchor.hh) treats this as an empty table and does not throw..
             // NotoSans Regular can trigger this. See https://github.com/SixLabors/Fonts/issues/417
-            _ => Empty,
+            _ => EmptyAnchorTable,
         };
     }
 

tests/Images/ReferenceOutput/TestIssue_468-.png

@@ -0,0 +1,42 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Text;
+
+namespace SixLabors.Fonts.Tests.Issues;
+
+public class Issues_468
+{
+    [Fact]
+    public void TestIssue_468()
+    {
+        StringBuilder stringBuilder = new();
+        stringBuilder
+            .AppendLine("Latin: The quick brown fox jumps over the lazy dog.")
+            .AppendLine("Arabic (RTL & Shaping): نص حكيم له سر قاطع وذو شأن عظيم");
+
+        string text = stringBuilder.ToString();
+        FontCollection fontCollection = new();
+
+        string consola = fontCollection.Add(TestFonts.Consola).Name;
+        string arabic = fontCollection.Add(TestFonts.NotoSansArabicRegular).Name;
+
+        FontFamily mainFontFamily = fontCollection.Get(consola);
+        Font mainFont = mainFontFamily.CreateFont(50, FontStyle.Regular);
+
+        TextOptions options = new(mainFont)
+        {
+            FallbackFontFamilies =
+            [
+                fontCollection.Get(arabic),
+            ],
+        };
+
+        // 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,
+            options,
+            includeGeometry: false);
+    }
+}

tests/SixLabors.Fonts.Tests/Fonts/NotoSansArabic-Regular.ttf

@@ -10,16 +10,6 @@ public class Issues_469
     [Fact]
     public void Test_Issue_469()
     {
-        const string arialFontName = "Arial";
-        const string inconsolataFontName = "Inconsolata";
-        const string nanumGothicCodingFontName = "NanumGothicCoding";
-        const string cousineFontName = "Cousine";
-        const string notoSansScThinFontName = "Noto Sans SC Thin";
-        const string notoSansJpThinFontName = "Noto Sans JP Thin";
-        const string notoNaskhArabicFontName = "Noto Naskh Arabic";
-        const string sarabunFontName = "Sarabun";
-        const string hindFontName = "Hind";
-
         StringBuilder stringBuilder = new();
         stringBuilder.AppendLine("Latin: The quick brown fox jumps over the lazy dog.")
             .AppendLine("Cyrillic: Съешь же ещё этих мягких французских булок.")
@@ -33,33 +23,33 @@ public void Test_Issue_469()
             .AppendLine("Devanagari (Conjuncts): ऋषियों को सताने वाले राक्षसों का अंत हो गया");
 
         string text = stringBuilder.ToString();
-        FontCollection fontCollection = new();
-        fontCollection.Add(TestFonts.Arial);
-        fontCollection.Add(TestFonts.CousineRegular);
-        fontCollection.Add(TestFonts.HindRegular);
-        fontCollection.Add(TestFonts.NanumGothicCodingRegular);
-        fontCollection.Add(TestFonts.InconsolataRegular);
-        fontCollection.Add(TestFonts.NotoNaskhArabicRegular);
-        fontCollection.Add(TestFonts.NotoSansHKVariableFontWght);
-        fontCollection.Add(TestFonts.NotoSansJPRegular);
-        fontCollection.Add(TestFonts.NotoSansSCRegular);
-        fontCollection.Add(TestFonts.SarabunRegular);
 
-        FontFamily mainFontFamily = fontCollection.Get(arialFontName);
+        FontCollection fontCollection = new();
+        string arial = fontCollection.Add(TestFonts.Arial).Name;
+        string cousine = fontCollection.Add(TestFonts.CousineRegular).Name;
+        string hind = fontCollection.Add(TestFonts.HindRegular).Name;
+        string nanumGothicCoding = fontCollection.Add(TestFonts.NanumGothicCodingRegular).Name;
+        string inconsolata = fontCollection.Add(TestFonts.InconsolataRegular).Name;
+        string notoNaskhArabic = fontCollection.Add(TestFonts.NotoNaskhArabicRegular).Name;
+        string notoSansJpThin = fontCollection.Add(TestFonts.NotoSansJPRegular).Name;
+        string notoSansScThin = fontCollection.Add(TestFonts.NotoSansSCRegular).Name;
+        string sarabun = fontCollection.Add(TestFonts.SarabunRegular).Name;
+
+        FontFamily mainFontFamily = fontCollection.Get(arial);
         Font mainFont = mainFontFamily.CreateFont(30, FontStyle.Regular);
 
         TextOptions options = new(mainFont)
         {
             FallbackFontFamilies =
             [
-                fontCollection.Get(inconsolataFontName),
-                fontCollection.Get(nanumGothicCodingFontName),
-                fontCollection.Get(cousineFontName),
-                fontCollection.Get(notoSansScThinFontName),
-                fontCollection.Get(notoSansJpThinFontName),
-                fontCollection.Get(notoNaskhArabicFontName),
-                fontCollection.Get(sarabunFontName),
-                fontCollection.Get(hindFontName),
+                fontCollection.Get(inconsolata),
+                fontCollection.Get(nanumGothicCoding),
+                fontCollection.Get(cousine),
+                fontCollection.Get(notoSansScThin),
+                fontCollection.Get(notoSansJpThin),
+                fontCollection.Get(notoNaskhArabic),
+                fontCollection.Get(sarabun),
+                fontCollection.Get(hind),
             ],
         };
 

tests/SixLabors.Fonts.Tests/Fonts/SofiaSansCondensed-ExtraLight-Regular.ttf

@@ -0,0 +1,49 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Text;
+
+namespace SixLabors.Fonts.Tests.Issues;
+
+public class Issues_470
+{
+    [Fact]
+    public void Test_Issue_470()
+    {
+        StringBuilder stringBuilder = new();
+        stringBuilder.AppendLine("Latin: The quick brown fox jumps over the lazy dog.")
+            .AppendLine("Cyrillic: Съешь же ещё этих мягких французских булок.")
+            .AppendLine("Greek: Ζαφείρι δέξου πάγκαλο, βαθῶν ψυχῆς τὸ σῆμα.")
+            .AppendLine("Chinese: 敏捷的棕色狐狸跳过了懒狗")
+            .AppendLine("Japanese: いろはにほへと ちりぬるを")
+            .AppendLine("Korean: 다람쥐 헌 쳇바퀴에 타고파")
+            .AppendLine("Arabic (RTL & Shaping): نص حكيم له سر قاطع وذو شأن عظيم")
+            .AppendLine("Hebrew (RTL): דג סקרן שט בים מאוכזב ולפתע מצא חברה")
+            .AppendLine("Thai (Complex): เป็นมนุษย์สุดประเสริฐเลิศคุณค่า")
+            .AppendLine("Devanagari (Conjuncts): ऋषियों को सताने वाले राक्षसों का अंत हो गया");
+
+        string text = stringBuilder.ToString();
+
+        FontCollection fontCollection = new();
+        string arial = fontCollection.Add(TestFonts.Arial).Name;
+        string sofia = fontCollection.Add(TestFonts.SofiaSansCondensedLight).Name;
+
+        FontFamily mainFontFamily = fontCollection.Get(arial);
+        Font mainFont = mainFontFamily.CreateFont(30, FontStyle.Regular);
+
+        TextOptions options = new(mainFont)
+        {
+            FallbackFontFamilies =
+            [
+                fontCollection.Get(sofia),
+            ],
+        };
+
+        // 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,
+            options,
+            includeGeometry: false);
+    }
+}

tests/SixLabors.Fonts.Tests/Fonts/consola.ttf

@@ -285,6 +285,12 @@ public static class TestFonts
 
     public static string SarabunRegular => GetFullPath("Sarabun-Regular.ttf");
 
+    public static string NotoSansArabicRegular => GetFullPath("NotoSansArabic-Regular.ttf");
+
+    public static string Consola => GetFullPath("consola.ttf");
+
+    public static string SofiaSansCondensedLight => GetFullPath("SofiaSansCondensed-ExtraLight-Regular.ttf");
+
     public static Stream TwemojiMozillaData() => OpenStream(TwemojiMozillaFile);
 
     public static Stream SegoeuiEmojiData() => OpenStream(SegoeuiEmojiFile);