We can discard frames from an animated image if the memory footprint
exceeds the threshold. This will cause us to redecode frames on demand
instead. However decoders can fail to produce the same results on
subsequent runs due to differences in memory pressure, etc. If this
happens our state can get inconsistent. In particular, if we keep
failing on the first frame, we end up in an infinite loop on the decoder
thread.
Since we don't have the owning image to signal, as we had to release our
reference to it after the first pass, we can do little but stop decoding.
From the user's perspective, the animation will come to a stop.
We should only attempt to discard animation image frames after passing
the frame threshold on the very first pass on the animation. Redecodes
are already in the correct state, as it will discard frames as it
advances the animation. This patch makes it clear what it should be
doing when, but there should be no functional change.
Cosmin Sabou
Andrew Osmond