The biggest one is avoiding a bunch of bit reversals by keeping
numbers in bit-reversed form for as long as we can.
Also reduced the hashing rounds: just 2 rounds seems to be enough
for a reasonable amount of statistical independence on both the
scrambling and shuffling. I tested both independently, keeping
the other with no scrambling/shuffling respectively. This makes
sense because in normal contexts 3 is enough, but in this case
both act as input to yet another hash which is effectively doing
more rounds.
Turns out it causes interference with the Sobol sampler.
Also tweaked some other things about sampling after removing
golden ratio sampling, to make things better.
This limits the number of samples per dimension to 2^16, but that
should be more than enough for any rendering situation. And this
reduces the direction numbers table size by a factor of 4.
This commit also takes advantage of the reduced bit space to
provide even better Owen scrambling, by utilizing the unused
16 bits for better mixing.
- Added an additional scramble round to the Owen scrambling, with
new optimized constants.
- Reordered the dimensions of the direction numbers to improve 2d
projections between adjecent dimensions. Only did this for
dimensions under ~40.
This produces identical results, but generates the direction
vectors from the original sources at build time. This makes
the source code quite a bit leaner, and will also make it easier
to play with other direction vectors in the future if the
opportunity arises.
