CBLC — Color Bitmap Location Table (OpenType 1.9)
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.
OpenType specification