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LibGfx: Use ZlibCompressor for compressing PNG files

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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
This commit is contained in:
Karol Kosek 2022-06-17 09:27:39 +02:00 • committed by Linus Groh
parent 0de0de3536
commit 9aafaec259
1 changed files with 15 additions and 63 deletions
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78
Userland/Libraries/LibGfx/PNGWriter.cpp
View file

@ -8,6 +8,7 @@
#include <AK/Concepts.h>
#include <AK/String.h>
#include <LibCompress/Zlib.h>
#include <LibCrypto/Checksum/CRC32.h>
#include <LibGfx/Bitmap.h>
#include <LibGfx/PNGWriter.h>
@ -46,23 +47,6 @@ private:
String m_type;
};
class NonCompressibleBlock {
public:
void finalize(PNGChunk&);
void add_byte_to_block(u8 data, PNGChunk&);
u16 adler_s1() const { return m_adler_s1; }
u16 adler_s2() const { return m_adler_s2; }
private:
void add_block_to_chunk(PNGChunk&, bool);
void update_adler(u8);
bool full() { return m_non_compressible_data.size() == 65535; }
Vector<u8> m_non_compressible_data;
u16 m_adler_s1 { 1 };
u16 m_adler_s2 { 0 };
};
PNGChunk::PNGChunk(String type)
: m_type(move(type))
{
@ -118,40 +102,6 @@ void PNGChunk::add_u8(u8 data)
add(data);
}
void NonCompressibleBlock::add_byte_to_block(u8 data, PNGChunk& chunk)
{
m_non_compressible_data.append(data);
update_adler(data);
if (full()) {
add_block_to_chunk(chunk, false);
m_non_compressible_data.clear_with_capacity();
}
}
void NonCompressibleBlock::add_block_to_chunk(PNGChunk& png_chunk, bool last)
{
png_chunk.add_u8(last);
u16 len = m_non_compressible_data.size();
u16 nlen = ~len;
png_chunk.add_as_little_endian(len);
png_chunk.add_as_little_endian(nlen);
png_chunk.add(m_non_compressible_data.data(), m_non_compressible_data.size());
}
void NonCompressibleBlock::finalize(PNGChunk& chunk)
{
add_block_to_chunk(chunk, true);
}
void NonCompressibleBlock::update_adler(u8 data)
{
m_adler_s1 = (m_adler_s1 + data) % 65521;
m_adler_s2 = (m_adler_s2 + m_adler_s1) % 65521;
}
void PNGWriter::add_chunk(PNGChunk& png_chunk)
{
png_chunk.store_data_length();
@ -190,27 +140,29 @@ void PNGWriter::add_IDAT_chunk(Gfx::Bitmap const& bitmap)
PNGChunk png_chunk { "IDAT" };
png_chunk.reserve(bitmap.size_in_bytes());
u16 CMF_FLG = 0x81d;
png_chunk.add_as_big_endian(CMF_FLG);
NonCompressibleBlock non_compressible_block;
ByteBuffer uncompressed_block_data;
uncompressed_block_data.ensure_capacity(bitmap.size_in_bytes() + bitmap.height());
for (int y = 0; y < bitmap.height(); ++y) {
non_compressible_block.add_byte_to_block(0, png_chunk);
uncompressed_block_data.append(0);
for (int x = 0; x < bitmap.width(); ++x) {
auto pixel = bitmap.get_pixel(x, y);
non_compressible_block.add_byte_to_block(pixel.red(), png_chunk);
non_compressible_block.add_byte_to_block(pixel.green(), png_chunk);
non_compressible_block.add_byte_to_block(pixel.blue(), png_chunk);
non_compressible_block.add_byte_to_block(pixel.alpha(), png_chunk);
uncompressed_block_data.append(pixel.red());
uncompressed_block_data.append(pixel.green());
uncompressed_block_data.append(pixel.blue());
uncompressed_block_data.append(pixel.alpha());
}
}
non_compressible_block.finalize(png_chunk);
png_chunk.add_as_big_endian(non_compressible_block.adler_s2());
png_chunk.add_as_big_endian(non_compressible_block.adler_s1());
auto maybe_zlib_buffer = Compress::ZlibCompressor::compress_all(uncompressed_block_data);
if (!maybe_zlib_buffer.has_value()) {
// FIXME: Handle errors.
VERIFY_NOT_REACHED();
}
auto zlib_buffer = maybe_zlib_buffer.release_value();
png_chunk.add(zlib_buffer.data(), zlib_buffer.size());
add_chunk(png_chunk);
}