After thinking about this and after some discussion with other
people, I now believe that hierarchical instancing isn't actually
that useful in practice for rendering.
Single-level instancing is still supported, of course.
This allows the error messages to be more informative by including
dynamically determined information.
Also made a utility function for ensuring that nodes get closed.
All rendering code is commented out for now. It will need to be
largely rewritten after this refactor is done, most likely.
This commit gets the basic new scene parsing working, with the basic
new data structures.
Specifically:
1. Factored out color exporting.
2. Switched floating point writing to use .format() with 6 digits
of precision. The main gain here is that numbers like 1.0
don't print with a bunch of useless trailing zeros.
The importance change here is bundling object data and its
instances together. This makes it possible to process the
scene data (e.g. for splitting, dicing, and de-instancing)
without having to cache arbitrary amounts of scene data.
In other words, this should allow for much more efficient
scene processing down the line.
Before this it needed SSE 4.1, which is not strictly present on
all x86-64 platforms. This will still compile the faster path if
SSE 4.1 is available, but has an alternate path as well for all
x86-64 platforms.
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.
Due to the undefined behavior of shifting a number by its
bit-width, the Sobol sampler would panic when sample index
`1 << 15` was requested.
This fixes it without introducing any additional checks or
operations.
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.
