In unbounded mode, the read and write pointers are free to move
independently of one another. This is useful where the input and output
streams are progressing at the same rate on average, and we want to keep
the latency stable in the event than an underrun or overrun occurs.
If an underrun occurs (i.e., there is not enough data in the buffer to
satisfy a read request), the missing values with be filled with zeros. When
the writer catches up, the same number of values will be skipped from the
input.
If an overrun occurs (i.e., there is not enough free space in the buffer to
satisfy a write request), excess values will be discarded. When the reader
catches up, the same number of values will be zeroed in the output.
Unbounded mode is currently unused since our audio input and output
streams are not synchronised. This will be implemented in a later commit.
Also reimplemented as a lock-free queue which is safer for use in audio
device callbacks.
If a new playback is started while the previous playback is still flushing,
we simply allow the stream to continue playing and effectively cancel the
flush. In general this is not safe because there may not be enough data in
the buffer to avoid underrunning. We could handle this better later by
trying to insert the right number of silent samples into the buffer, but
for now just completely stop the previous stream before starting the new
one.
Automatically restarting playback once draining has completed could result
in playback starting too early (i.e., before there is enough data in the
ring buffer to avoid underrunning). `audio_playbackData` will keep invoking
`start` until it returns true anyway, so we can just allow draining to
complete normally and wait for `start` to be called again.
These are implemented as ScrollLock+Up/Down for volume up and down, and
ScrollLock+M to toggle audio mute. These should prove useful especially
when Looking Glass now supports streaming audio, and the volume is
defined in the guest and set on the output stream.
This prevents LGMP_ERR_QUEUE_FULL from happening with high polling rate
mice, which is caused by receiving many more mouse events while the
guest cursor warps, triggering more warps.
