While most of HarfBuzz's object types are specific to the shaping process, blobs are somewhat different.
Blobs are an abstraction designed to negotiate lifecycle and
permissions for raw pieces of data. For example, when you load
the raw font data into memory and want to pass it to HarfBuzz,
you do so in a
This allows you to take advantage of HarfBuzz's
callbacks. If you allocated the memory for the data using
malloc(), you would create the blob using
hb_blob_create (data, length, HB_MEMORY_MODE_WRITABLE, data, free)
That way, HarfBuzz will call
free() on the
allocated memory whenever the blob drops its last reference and
is deconstructed. Consequently, the user code can stop worrying
about freeing memory and let the reference-counting machinery
take care of that.
Most of the time, blobs are read-only, facilitating their use in immutable objects.