CBLC — Color Bitmap Location Table

Table structure

The CBLC table provides embedded bitmap locators. It is used together with the CBDT table, which provides embedded, color bitmap glyph data. The formats of these two tables are backward compatible with the EBDT and EBLC tables used for embedded monochrome and grayscale bitmaps.

The CBLC table begins with a header containing the table version and number of strikes.

CblcHeader

Type	Name	Description
uint16	majorVersion	Major version of the CBLC table, = 3.
uint16	minorVersion	Minor version of the CBLC table, = 0.
uint32	numSizes	Number of BitmapSize records.
BitmapSize	bitmapSizes	BitmapSize records array.

Note that the first version of the CBLC table is 3.0.

Each strike is defined by one BitmapSize record.

BitmapSize Record

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.