PNGWriter sets up one dummy scanline with the same width as the other
scanlines in order to allow addressing the "previous scanline" without
complicating the code.
By using a FixedArray instead of a VLA, we sidestep the risk of stack
overflow and instead get something that can signal OOM.
This patch basically uses the TRY() macro throughout PNGWriter instead
of relying on the MUST()'ing wrappers in Vector and ByteBuffer.
One FIXME was killed in the making of this patch. :^)
This is a first step towards handling PNG encoding failures instead of
just falling over and crashing the program.
This initial step will cause encode() to return an error if the final
ByteBuffer copy fails to allocate. There are more potential failures
that will be surfaced by subsequent commits.
Two FIXMEs were killed in the making of this patch. :^)
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
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}