Specify the Bitmap Handle
Bitmap Handle. The initial value is 0. Valid range values 0 to 31.
Handles 16 to 31 are defined by the FT800 for built-in font.
Users can define new bitmaps using handles from 0 to 14.
can even define a bitmap using handle 15.
The value of handle is part of the graphics context, as described in section 4.1 in FT800 Series Programmer Guide.PDF from FTDI.