While for a general purpose encoder a good balance between compression
speed and size by default is important, in case of PNG it don't matter
that much, as it was said in #14594.
Also note that it's not the best we can have. We use zlib's compression
level, which has a range of 0-4, while our deflate implementation ranges
from 0 to 5.
Is it another great upgrade to our PNG encoder like in 9aafaec259?
Well, not really - it's not a 2x or 55x improvement like you saw there,
but still it saves something:
- a screenshot of a blank Serenity desktop dropped from about 45 KiB
to 40 KiB.
- re-encoding NASA photo of the Earth to PNG again saves about 25%
(16.5 MiB -> 12.3 MiB), compared to not using filters.
[1]: https://commons.wikimedia.org/wiki/File:The_Blue_Marble_(remastered).jpg
Previously we were hand-writing all the Zlib and raw Deflated data
structures here, but now PNGs will be compressed using ZlibCompressor
which will actually try to compress something! :^)
Note that we don't do any filtering that should help compress data even
more, but even now the results are pretty good:
- screenshots of my Serenity desktop are take now about 55 KiB, where
previously it was 3 MiB.
- re-encoding NASA photo of the Earth[1] to PNG shows a 2x improvement
(34.3 MiB -> 16.5 MiB).
[1]: https://commons.wikimedia.org/wiki/File:The_Blue_Marble_(remastered).jpg
Apologies for the enormous commit, but I don't see a way to split this
up nicely. In the vast majority of cases it's a simple change. A few
extra places can use TRY instead of manual error checking though. :^)
The two Adler32 checksums are u16 and these two getters were mistakenly
left as u32 when PNGChunk::add_as_big_endian() was templated leading
to corrupted IDAT fields in our PNGs.
Before this change PNGWriter::add_chunk used to make a copy of
PNGChunk's ByteBuffer to prepend the size of the data.
With this change, 4-byte space is saved from the beginning and written
at the end of the operation. Avoiding this copy yields significant
speed up.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
With this patch it is possible to create PNG files. Only minimal options
are supported. The PNG is created with one big IDAT chunk containing
only non-compressible DEFLATE blocks.
.jpg){kind=link}