In order to better facilitate the change from block stream order to non-block stream order,
a lot of changes were introduced to the way that we feed texture data to the compressors. This
data is embodied in the CompressionJob struct. We have made it so that the compression job
points to both the in and out pointers for our compressed and uncompressed data. Furthermore,
we have made sure that the struct also contains the format that its compressing for, so that if
any threading programs would like to chop up a compression job into smaller chunks based on the
format, it doesn't need to know the format explicitly, it just needs to know certain properties
about the format.
Moreover, the user can now define the start and end pixels from which we would like to compress
to. We can compress subsets of data by changing the in and out pointers and the width and height
values. The compressors will read data linearly until they reach the out pixels based on the width
of the given pixel.
In general, we want to use this algorithm only with self-contained compression
lists. As such, we've added all of the proper synchronization primitives in
the list object itself. That way, different threads that are working on the
same list will be able to communicate. Ideally, this should eliminate the
number of user-space context switches that happen. Whether or not this is
faster than the other synchronization algorithms that we've tried remains
to be seen...
This is a first pass of what I believe to be a not too terrible
implementation of a cooperative thread-based compressor. The idea is
simple... If a compressor is invoked with the same parameters on multiple
threads, then the threads cooperate via an atomic counter to compress the
texture. Each thread can take as long as possible until the texture is finished.
If a caller calls a compression routine that has different parameters, then
it will help the current compression finish before starting on its own compression. In this
way, we can split the textures up among the threads and guarantee that we maximize the
resource usage between them. I.e. this becomes more efficient:
Thread 1: Thread 2: Thread N:
tex0 texN tex(N-1)N
tex1 texN+1 tex(N-1)(N+1)
.. .. ..
texN-1 tex2N tex(N-1)N
I have not tested this for bugs, so I'm still not completely convinced that it is deadlock-free
although it should be...
Changed the function prototype to match that of the typedef in the rest of the library, and fixed a bug where we would iterate too far with the initial buffer.
