implement glyph index getter for the 3 implemented truetype cmap sub tables

src/UglyToad.PdfPig/Fonts/TrueType/Tables/CMapSubTables/ByteEncodingCMapTable.cs

@@ -6,29 +6,40 @@
     /// </summary>
     internal class ByteEncodingCMapTable : ICMapSubTable
     {
+        private const int GlyphMappingLength = 256;
+        private readonly byte[] glyphMapping;
+
         public int PlatformId { get; }
 
         public int EncodingId { get; }
 
-        private ByteEncodingCMapTable(int platformId, int encodingId)
+        private ByteEncodingCMapTable(int platformId, int encodingId, byte[] glyphMapping)
         {
+            this.glyphMapping = glyphMapping;
             PlatformId = platformId;
             EncodingId = encodingId;
         }
 
         public static ByteEncodingCMapTable Load(TrueTypeDataBytes data, int platformId, int encodingId)
         {
+            // ReSharper disable UnusedVariable
             var length = data.ReadUnsignedShort();
             var version = data.ReadUnsignedShort();
+            // ReSharper restore UnusedVariable
 
-            var glyphMapping = data.ReadByteArray(256);
+            var glyphMapping = data.ReadByteArray(GlyphMappingLength);
 
-            return new ByteEncodingCMapTable(platformId, encodingId);
+            return new ByteEncodingCMapTable(platformId, encodingId, glyphMapping);
         }
 
         public int CharacterCodeToGlyphIndex(int characterCode)
         {
-            throw new System.NotImplementedException();
+            if (characterCode < GlyphMappingLength || characterCode >= GlyphMappingLength)
+            {
+                return 0;
+            }
+
+            return glyphMapping[characterCode];
         }
     }
 }

src/UglyToad.PdfPig/Fonts/TrueType/Tables/CMapSubTables/Format4CMapTable.cs

@@ -34,7 +34,26 @@ namespace UglyToad.PdfPig.Fonts.TrueType.Tables.CMapSubTables
 
         public int CharacterCodeToGlyphIndex(int characterCode)
         {
-            throw new NotImplementedException();
+            for (var i = 0; i < Segments.Count; i++)
+            {
+                var segment = Segments[i];
+
+                if (segment.EndCode < characterCode || segment.StartCode > characterCode)
+                {
+                    continue;
+                }
+
+                if (segment.IdRangeOffset == 0)
+                {
+                    return (characterCode + segment.IdDelta) % ushort.MaxValue;
+                }
+
+                var offset = segment.IdRangeOffset / 2 + (characterCode - segment.StartCode);
+
+                return GlyphIds[offset - Segments.Count + i];
+            }
+
+            return 0;
         }
 
         public static Format4CMapTable Load(TrueTypeDataBytes data, int platformId, int encodingId)

src/UglyToad.PdfPig/Fonts/TrueType/Tables/CMapSubTables/HighByteMappingCMapTable.cs

@@ -10,25 +10,35 @@
     /// </summary>
     internal class HighByteMappingCMapTable : ICMapSubTable
     {
+        private readonly IReadOnlyDictionary<int, int> characterCodesToGlyphIndices;
+
         public int PlatformId { get; }
 
         public int EncodingId { get; }
 
-        public HighByteMappingCMapTable(int platformId, int encodingId)
+        private HighByteMappingCMapTable(int platformId, int encodingId, IReadOnlyDictionary<int, int> characterCodesToGlyphIndices)
         {
+            this.characterCodesToGlyphIndices = characterCodesToGlyphIndices ?? throw new ArgumentNullException(nameof(characterCodesToGlyphIndices));
             PlatformId = platformId;
             EncodingId = encodingId;
         }
 
         public int CharacterCodeToGlyphIndex(int characterCode)
         {
-            throw new NotImplementedException();
+            if (!characterCodesToGlyphIndices.TryGetValue(characterCode, out var index))
+            {
+                return 0;
+            }
+
+            return index;
         }
 
         public static HighByteMappingCMapTable Load(TrueTypeDataBytes data, int numberOfGlyphs, int platformId, int encodingId)
         {
+            // ReSharper disable UnusedVariable
             var length = data.ReadUnsignedShort();
             var version = data.ReadUnsignedShort();
+            // ReSharper restore UnusedVariable
 
             var subHeaderKeys = new int[256];
             var maximumSubHeaderIndex = 0;
@@ -83,7 +93,7 @@
                 }
             }
 
-            return new HighByteMappingCMapTable(platformId, encodingId);
+            return new HighByteMappingCMapTable(platformId, encodingId, characterCodeToGlyphId);
         }
 
         public struct SubHeader