In order to avoid problems with mutable references,
the approach is to use the eval sender for non-parallel.
Computations will still be done synchronously
with the fake synchronous rayon module.
* Skip baselines earlier in the evaluator
We know that we'll throw them away anyway, so there is no point in even sending them to Sender and comparing them with others once we used them for the best candidate size.
* Simplify comparison logic
* Improve performance consistency
Switch from HashMap / HashSet to IndexMap / IndexSet for consistent iteration order of various options and, as a result, more predictable performance.
libdeflater is a Rust wrapper around
[libdeflate](https://github.com/ebiggers/libdeflate) - an alternative
heavily optimised library for deflate/zlib/gzip compression and
decompression that is intended for situations where upper bounds of the
output are well-known.
In my benchmarks on test files in the repo it has shown to be usually
both slightly faster and providing better compressed output than
cloudflare-zlib, but in some cases showing the opposite, so rather
than swapping defaults, it's currently provided as another option,
similarly to zopfli.
Since it's not strictly better in all cases, I'm not providing median
numbers, but you can check distribution histograms for time and size
differences here (all using `oxipng -o 6 -t 6 -P`):
https://docs.google.com/spreadsheets/d/1WOKgeYZBhLkQvMGAC36snN4azilElzOFhx63RJu0EZY/edit?usp=sharing
* Avoid using time API when we don't need it
This avoids a syscall to the time API when the result is ignored later anyway.
This allows to use the library with default options on wasm32-unknown-unknown, where the unimplemented syscall would panic otherwise.
* eval_send doesn't need to be an Option
We can drop the value manually, thus avoiding unwrap on each access.
* Keep single `use rayon::prelude::*`
If either `rayon` is already imported, then `rayon::prelude::*` should always resolve.
* Extract comparator
* Fully enable non-parallel mode
* Fix verbose message
* No cloning when restoring original data
* Make reductions return a new uncompressed image
Partially fixes#145
* Async reduction evaluator
* Assert
* Faster bit depth check
* Also try 4-bit depth for small-depth images
* Skip test when using miniz
* Ensure palette is trimmed after depth reduction
Fixes#159
* Fudge factor for reductions to prefer better reductions even if gzip estimation says otherwise
* Move reductions to a module. Make copy instead of changing in-place.
* Alpha reductions
* Immutable color reductions
* Immutable interlace reductions
* Compress alpha with strategy sensitive to repetitions
* Update reductions flag when alpha changed
* Avoid needlessly cloning out-of-date idat_data and temp raw_data
