public static BitmapSizeTable ReadBitmapSizeTable(BinaryReader reader)
{
//EBLC's BitmapSize Table (https://docs.microsoft.com/en-us/typography/opentype/spec/eblc)
//Type Name Description
//Offset32 indexSubTableArrayOffset Offset to IndexSubtableArray, from beginning of EBLC.
//uint32 indexTablesSize Number of bytes in corresponding index subtables and array.
//uint32 numberOfIndexSubTables There is an IndexSubtable for each range or format change.
//uint32 colorRef Not used; set to 0.
//SbitLineMetrics hori Line metrics for text rendered horizontally.
//SbitLineMetrics vert Line metrics for text rendered vertically.
//uint16 startGlyphIndex Lowest glyph index for this size.
//uint16 endGlyphIndex Highest glyph index for this size.
//uint8 ppemX Horizontal pixels per em.
//uint8 ppemY Vertical pixels per em.
//uint8 bitDepth The Microsoft rasterizer v.1.7 or greater supports the following bitDepth values, as described below: 1, 2, 4, and 8.
//int8 flags Vertical or horizontal(see Bitmap Flags, below).
//CBLC's BitmapSize Table (https://docs.microsoft.com/en-us/typography/opentype/spec/cblc)
//Type Name Description
//Offset32 indexSubTableArrayOffset Offset to index subtable from beginning of CBLC.
//uint32 indexTablesSize Number of bytes in corresponding index subtables and array.
//uint32 numberofIndexSubTables There is an index subtable for each range or format change.
//uint32 colorRef Not used; set to 0.
//SbitLineMetrics hori Line metrics for text rendered horizontally.
//SbitLineMetrics vert Line metrics for text rendered vertically.
//uint16 startGlyphIndex Lowest glyph index for this size.
//uint16 endGlyphIndex Highest glyph index for this size.
//uint8 ppemX Horizontal pixels per em.
//uint8 ppemY Vertical pixels per em.
//uint8 bitDepth In addtition to already defined bitDepth values 1, 2, 4, and 8
// supported by existing implementations, the value of 32 is used to
// identify color bitmaps with 8 bit per pixel RGBA channels.
//int8 flags Vertical or horizontal(see the Bitmap Flags section of the EBLC table chapter).
//The indexSubTableArrayOffset is the offset from the beginning of
//the CBLC table to the indexSubTableArray.
//Each strike has one of these arrays to support various formats and
//discontiguous ranges of bitmaps.The indexTablesSize is
//the total number of bytes in the indexSubTableArray and
//the associated indexSubTables.
//The numberOfIndexSubTables is a count of the indexSubTables for this strike.
//The rest of the CBLC table structure is identical to one already defined for EBLC.
BitmapSizeTable bmpSizeTable = new BitmapSizeTable();
bmpSizeTable.indexSubTableArrayOffset = reader.ReadUInt32();
bmpSizeTable.indexTablesSize = reader.ReadUInt32();
bmpSizeTable.numberOfIndexSubTables = reader.ReadUInt32();
bmpSizeTable.colorRef = reader.ReadUInt32();
BitmapSizeTable.ReadSbitLineMetrics(reader, ref bmpSizeTable.hori);
BitmapSizeTable.ReadSbitLineMetrics(reader, ref bmpSizeTable.vert);
bmpSizeTable.startGlyphIndex = reader.ReadUInt16();
bmpSizeTable.endGlyphIndex = reader.ReadUInt16();
bmpSizeTable.ppemX = reader.ReadByte();
bmpSizeTable.ppemY = reader.ReadByte();
bmpSizeTable.bitDepth = reader.ReadByte();
bmpSizeTable.flags = (sbyte)reader.ReadByte();
return(bmpSizeTable);
}
public static IndexSubTableBase CreateFrom(BitmapSizeTable bmpSizeTable, BinaryReader reader)
{
//read IndexSubHeader
//IndexSubHeader
//Type Name Description
//uint16 indexFormat Format of this IndexSubTable.
//uint16 imageFormat Format of EBDT image data.
//Offset32 imageDataOffset Offset to image data in EBDT table.
//There are currently five different formats used for the IndexSubTable,
//depending upon the size and type of bitmap data in the glyph ID range.
//Apple 'bloc' tables support only formats 1 through 3.
//The choice of which IndexSubTable format to use is up to the font manufacturer,
//but should be made with the aim of minimizing the size of the font file.
//Ranges of glyphs with variable metrics — that is,
//where glyphs may differ from each other in bounding box height, width, side bearings or
//advance — must use format 1, 3 or 4.
//Ranges of glyphs with constant metrics can save space by using format 2 or 5,
//which keep a single copy of the metrics information in the IndexSubTable rather
//than a copy per glyph in the EBDT table.
//In some monospaced fonts it makes sense to store extra white space around
//some of the glyphs to keep all metrics identical, thus permitting the use of format 2 or 5.
IndexSubHeader header = new IndexSubHeader(
reader.ReadUInt16(),
reader.ReadUInt16(),
reader.ReadUInt32()
);
switch (header.indexFormat)
{
case 1:
//IndexSubTable1: variable - metrics glyphs with 4 - byte offsets
//Type Name Description
//IndexSubHeader header Header info.
//Offset32 offsetArray[] offsetArray[glyphIndex] + imageDataOffset = glyphData sizeOfArray = (lastGlyph - firstGlyph + 1) + 1 + 1 pad if needed
{
int nElem = (bmpSizeTable.endGlyphIndex - bmpSizeTable.startGlyphIndex + 1);
uint[] offsetArray = Utils.ReadUInt32Array(reader, nElem);
//check 16 bit align padd
IndexSubTable1 subTable = new IndexSubTable1();
subTable.header = header;
subTable.offsetArray = offsetArray;
return(subTable);
}
case 2:
//IndexSubTable2: all glyphs have identical metrics
//Type Name Description
//IndexSubHeader header Header info.
//uint32 imageSize All the glyphs are of the same size.
//BigGlyphMetrics bigMetrics All glyphs have the same metrics; glyph data may be compressed, byte-aligned, or bit-aligned.
{
IndexSubTable2 subtable = new IndexSubTable2();
subtable.header = header;
subtable.imageSize = reader.ReadUInt32();
BigGlyphMetrics.ReadBigGlyphMetric(reader, ref subtable.BigGlyphMetrics);
return(subtable);
}
case 3:
//IndexSubTable3: variable - metrics glyphs with 2 - byte offsets
//Type Name Description
//IndexSubHeader header Header info.
//Offset16 offsetArray[] offsetArray[glyphIndex] + imageDataOffset = glyphData sizeOfArray = (lastGlyph - firstGlyph + 1) + 1 + 1 pad if needed
{
int nElem = (bmpSizeTable.endGlyphIndex - bmpSizeTable.startGlyphIndex + 1);
ushort[] offsetArray = Utils.ReadUInt16Array(reader, nElem);
//check 16 bit align padd
IndexSubTable3 subTable = new IndexSubTable3();
subTable.header = header;
subTable.offsetArray = offsetArray;
return(subTable);
}
case 4:
//IndexSubTable4: variable - metrics glyphs with sparse glyph codes
//Type Name Description
//IndexSubHeader header Header info.
//uint32 numGlyphs Array length.
//GlyphIdOffsetPair glyphArray[numGlyphs + 1] One per glyph.
{
IndexSubTable4 subTable = new IndexSubTable4();
subTable.header = header;
uint numGlyphs = reader.ReadUInt32();
GlyphIdOffsetPair[] glyphArray = subTable.glyphArray = new GlyphIdOffsetPair[numGlyphs + 1];
for (int i = 0; i <= numGlyphs; ++i) //***
{
glyphArray[i] = new GlyphIdOffsetPair(reader.ReadUInt16(), reader.ReadUInt16());
}
return(subTable);
}
case 5:
//IndexSubTable5: constant - metrics glyphs with sparse glyph codes
//Type Name Description
//IndexSubHeader header Header info.
//uint32 imageSize All glyphs have the same data size.
//BigGlyphMetrics bigMetrics All glyphs have the same metrics.
//uint32 numGlyphs Array length.
//uint16 glyphIdArray[numGlyphs] One per glyph, sorted by glyph ID.
{
IndexSubTable5 subTable = new IndexSubTable5();
subTable.header = header;
subTable.imageSize = reader.ReadUInt32();
BigGlyphMetrics.ReadBigGlyphMetric(reader, ref subTable.BigGlyphMetrics);
subTable.glyphIdArray = Utils.ReadUInt16Array(reader, (int)reader.ReadUInt32());
return(subTable);
}
}
//The size of the EBDT image data can be calculated from the IndexSubTable information.
//For the constant-metrics formats(2 and 5) the image data size is constant,
//and is given in the imageSize field.For the variable metrics formats(1, 3, and 4)
//image data must be stored contiguously and in glyph ID order,
//so the image data size may be calculated by subtracting the offset for
//the current glyph from the offset of the next glyph.
//Because of this, it is necessary to store one extra element in the offsetArray pointing
//just past the end of the range’s image data.
//This will allow the correct calculation of the image data size for the last glyph in the range.
//Contiguous, or nearly contiguous,
//ranges of glyph IDs are handled best by formats 1, 2, and 3 which
//store an offset for every glyph ID in the range.
//Very sparse ranges of glyph IDs should use format 4 or 5 which explicitly
//call out the glyph IDs represented in the range.
//A small number of missing glyphs can be efficiently represented in formats 1 or 3 by having
//the offset for the missing glyph be followed by the same offset for
//the next glyph, thus indicating a data size of zero.
//The only difference between formats 1 and 3 is
//the size of the offsetArray elements: format 1 uses uint32s while format 3 uses uint16s.
//Therefore format 1 can cover a greater range(> 64k bytes)
//while format 3 saves more space in the EBLC table.
//Since the offsetArray elements are added to the imageDataOffset base address in the IndexSubHeader,
//a very large set of glyph bitmap data could be addressed by splitting it into multiple ranges,
//each less than 64k bytes in size,
//allowing the use of the more efficient format 3.
//The EBLC table specification requires 16 - bit alignment for all subtables.
//This occurs naturally for IndexSubTable formats 1, 2, and 4,
//but may not for formats 3 and 5,
//since they include arrays of type uint16.
//When there is an odd number of elements in these arrays
//**it is necessary to add an extra padding element to maintain proper alignment.
return(null);
}
