The function is used to rebuild any caches associated with the bitmap.
In the case of purgeable bitmaps, this call ensures that the pixels
are decoded for drawing, and therefore prefetching techniques
implemented by callers can be leveraged.
and lower the threshold of bitmap size for using ashmem().
For the decoding logic, we now go through the "non-purgeable" path if isShareable is false,
irrespective of the value of the purgeable flag.
BitmapFactory::Options now let you specify if the resulting bitmap can be
"purgeable". If so, then its decoded pixels may be purged when not actively
being drawn, freeing up that RAM. When such a bitmap is drawn, it will
automatically be re-decoded on demand. This is done by having the bitmap
keep a reference/copy of the encoded data.
Where it is a reference or a copy is controlled by the "shareable" flag in
Options. If this is true, the implementation *may* just reference the encode
data (e.g. a file descriptor) rathern than making a complete copy of it.
Currently, purgeable is not supported for generic inputstreams, but is
enabled for byte-array, file-descriptor, and assets, though for impl
reasons only file-descripts are currently enabled for "shareable", but that
may change in the future.
