BLGlyphBuffer Class Referencefinal [¶]
Glyph buffer [C++ API].
Can hold either text or glyphs and provides basic memory management that is used for text shaping, character to glyph mapping, glyph substitution, and glyph positioning.
Glyph buffer provides two separate buffers called 'primary' and 'secondary' that serve different purposes during processing. Primary buffer always holds actual text/glyph array, and secondary buffer is either used as a scratch buffer during glyph substitution or to hold glyph positions after the processing is complete and glyph positions were calculated.