protected override void ReadContentFrom(BinaryReader reader)
{
//-------------------------------------------
// GPOS/GSUB Header
// The GPOS/GSUB table begins with a header that contains a version number for the table. Two versions are defined.
// Version 1.0 contains offsets to three tables: ScriptList, FeatureList, and LookupList.
// Version 1.1 also includes an offset to a FeatureVariations table.
// For descriptions of these tables, see the chapter, OpenType Layout Common Table Formats .
// Example 1 at the end of this chapter shows a GPOS/GSUB Header table definition.
//
// GPOS/GSUB Header, Version 1.0
// Value Type Description
// uint16 MajorVersion Major version of the GPOS/GSUB table, = 1
// uint16 MinorVersion Minor version of the GPOS/GSUB table, = 0
// Offset16 ScriptList Offset to ScriptList table, from beginning of GPOS/GSUB table
// Offset16 FeatureList Offset to FeatureList table, from beginning of GPOS/GSUB table
// Offset16 LookupList Offset to LookupList table, from beginning of GPOS/GSUB table
//
// GPOS/GSUB Header, Version 1.1
// Value Type Description
// uint16 MajorVersion Major version of the GPOS/GSUB table, = 1
// uint16 MinorVersion Minor version of the GPOS/GSUB table, = 1
// Offset16 ScriptList Offset to ScriptList table, from beginning of GPOS/GSUB table
// Offset16 FeatureList Offset to FeatureList table, from beginning of GPOS/GSUB table
// Offset16 LookupList Offset to LookupList table, from beginning of GPOS/GSUB table
// Offset32 FeatureVariations Offset to FeatureVariations table, from beginning of GPOS/GSUB table (may be NULL)
long tableStartAt = reader.BaseStream.Position;
MajorVersion = reader.ReadUInt16();
MinorVersion = reader.ReadUInt16();
ushort scriptListOffset = reader.ReadUInt16(); // from beginning of table
ushort featureListOffset = reader.ReadUInt16(); // from beginning of table
ushort lookupListOffset = reader.ReadUInt16(); // from beginning of table
uint featureVariations = (MinorVersion == 1) ? reader.ReadUInt32() : 0; // from beginning of table
//-----------------------
//1. scriptlist
ScriptList = ScriptList.CreateFrom(reader, tableStartAt + scriptListOffset);
//-----------------------
//2. feature list
FeatureList = FeatureList.CreateFrom(reader, tableStartAt + featureListOffset);
//-----------------------
//3. lookup list
ReadLookupListTable(reader, tableStartAt + lookupListOffset);
//-----------------------
//4. feature variations
if (featureVariations > 0)
{
ReadFeatureVariations(reader, tableStartAt + featureVariations);
}
}
public static FeatureList CreateFrom(BinaryReader reader, long beginAt)
{
//https://www.microsoft.com/typography/otspec/chapter2.htm
//------------------
//FeatureList table
//------------------
//Type Name Description
//uint16 FeatureCount Number of FeatureRecords in this table
//struct FeatureRecord[FeatureCount] Array of FeatureRecords-zero-based (first feature has FeatureIndex = 0)-listed alphabetically by FeatureTag
//------------------
//FeatureRecord
//------------------
//Type Name Description
//Tag FeatureTag 4-byte feature identification tag
//Offset16 Feature Offset to Feature table-from beginning of FeatureList
//----------------------------------------------------
reader.BaseStream.Seek(beginAt, SeekOrigin.Begin);
//
FeatureList featureList = new FeatureList();
ushort featureCount = reader.ReadUInt16();
FeatureRecord[] featureRecords = new FeatureRecord[featureCount];
for (int i = 0; i < featureCount; ++i)
{
//read script record
featureRecords[i] = new FeatureRecord(
reader.ReadUInt32(), //feature tag
reader.ReadUInt16()); //Offset16
}
//read each feature table
FeatureTable[] featureTables = featureList.featureTables = new FeatureTable[featureCount];
for (int i = 0; i < featureCount; ++i)
{
FeatureRecord frecord = featureRecords[i];
(featureTables[i] = FeatureTable.CreateFrom(reader, beginAt + frecord.offset)).FeatureTag = frecord.featureTag;
}
return(featureList);
}
