The delay scale is roughly linear with respect to room size, however the
density is not linear with room size. The density is calculated by taking the
room size cubed, then normalized by some factor. Unnormalizing the density and
taking the cube root restores the original room size to use as a delay scale.
The patch also alters the delay and all-pass line lengths to be based on a 1
meter room size, so the the room size recovered from the density acts as a
direct multiple for the desired target length.
Note that the room scale range is unchanged (5m to 50m), so the minimum and
maximum delays are the same. It should also be noted that 50m may not be the
correct room size for a density value of 1. A density value of 1 corresponds to
an environment size of roughly 2.52m when converted from EAX (DENSITY_SCALE
should be 16 rather than 125000), but sizes that low result in undesirable
resonance in the feedback, indicating other changes are necessary for that to
work.
Semaphores allow for semi-persistent signals, compared to a condition variable
which requires a mutex for proper detection. A semaphore can be 'post'ed after
writing some data on one thread, and another thread will be able to recognize
it quickly even if the post occured in between checking for data and waiting.
This more correctly fixes a race condition with events since the mixer
shouldn't be using mutexes, and arbitrary wake-ups just to make sure an event
wasn't missed was quite inefficient.
To avoid having unknown user code running in the mixer thread that could
significantly delay the mixed output, a lockless ringbuffer is used for the
mixer to provide events that a secondary thread will pop off and process.
Rather than each buffer being individually allocated with a generated 'thunk'
ID that's used with a uint:ptr map, buffers are allocated in arrays of 64
within a vector. Each group of 64 has an associated 64-bit mask indicating
which are free to use, and the buffer ID is comprised of the two array indices
which directly locate the buffer (no searching, binary or otherwise).
Currently no buffers are actually deallocated after being allocated, though
they are reused. So an app that creates a ton of buffers once, then deletes
them all and uses only a couple from then on, will have a bit of waste, while
an app that's more consistent with the number of used buffers won't be a
problem. This can be improved by removing elements of the containing vector
that contain all-free buffers while there are plenty of other free buffers.
Also, this method can easily be applied to other resources, like sources.
Rather than hackily combining bit flags with the format, to increase the number
of potential flags. alBufferData now behaves as if calling alBufferStorageSOFT
with a flags value of 0.
The symbols are still there and exported to retain ABI compatibility, but they
no longer do anything except set an AL_INVALID_OPERATION error. They're also
removed from the function and enum tables, since they're not part of any
supported extension.
They're now decompressed on the fly in the mixer. This is not a significant
performance issue given that it only needs a 512-byte lookup table, and the
buffer stores half as much data (it may actually be faster, requiring less
overall memory).
