By choosing compress option, tvg tries to compress the data to reduce the binary size.
Since the compression has the double-edges sword, we provides an option to users
to select it by their demand. Basically, compression is better than non-compression.
After profiling, we decided to use the encoder/decoder of Guilherme R. Lampert's.
Here is the profiling result:
test.tvg: 296037 -> 243411 (-17%)
tiger.tvg: 54568 -> 50622 (-7%)
image-embedded.tvg: 2282 -> 1231 (-46%)
@Issue: https://github.com/Samsung/thorvg/issues/639
About compression method:
Lempel–Ziv–Welch (LZW) encoder/decoder by Guilherme R. Lampert
This is the compression scheme used by the GIF image format and the Unix 'compress' tool.
Main differences from this implementation is that End Of Input (EOI) and Clear Codes (CC)
are not stored in the output and the max code length in bits is 12, vs 16 in compress.
EOI is simply detected by the end of the data stream, while CC happens if the
dictionary gets filled. Data is written/read from bit streams, which handle
byte-alignment for us in a transparent way.
The decoder relies on the hardcoded data layout produced by the encoder, since
no additional reconstruction data is added to the output, so they must match.
The nice thing about LZW is that we can reconstruct the dictionary directly from
the stream of codes generated by the encoder, so this avoids storing additional
headers in the bit stream.
The output code length is variable. It starts with the minimum number of bits
required to store the base byte-sized dictionary and automatically increases
as the dictionary gets larger (it starts at 9-bits and grows to 10-bits when
code 512 is added, then 11-bits when 1024 is added, and so on). If the dictionary
is filled (4096 items for a 12-bits dictionary), the whole thing is cleared and
the process starts over. This is the main reason why the encoder and the decoder
must match perfectly, since the lengths of the codes will not be specified with
the data itself.
We can replace the system logger method by changing single line print source in common,
This also helps to remove the THORVG_LOG_ENABLED macro from each use-cases.
TVGLOG(): To print the hint & tip messages for users.
TVGERR(): To print the error message for debugging.
@Issues: https://github.com/Samsung/thorvg/issues/36
tvg saver is a new module to export tvg files.
In this patch, it also contains the infrastructure of saver module
to expand other types of savers such as png, jpg, etc.
To save the tvg file from a paint, you can use the Saver feature, for example:
auto saver = tvg::Saver::gen();
saver->save(paint, "sample.tvg");
saver->sync();
Later, you can read the "sample.tvg" using Picture.
auto picture = tvg::Picture::gen();
picture->load("sample.tvg");
...
The behavior of the saver will work on sync/async based on the threading setting of the initializer.
Thus if you wish to have a benefit of it, you must call sync() after the save() in the proper delayed time.
Otherwise, you can call sync() immediately.
Note that, the asynchronous tasking is depent on the saver module implementation.
Also, you need to enable tvg saver/loader modules from meson option. (yet this feature is under the beta)
@API Addition:
Result Saver::save(std::unique_ptr<Paint> paint, const std::string& path) noexcept;
Result Saver::sync() noexcept;
@Examples: tvgSaver
@Co-author: Mira Grudzinska <m.grudzinska@samsung.com>
The Saver class enables to save any Paint object (Scene, Shape, Picture)
in a binary file. To read the file the tvg loader should be used.
To save a paint a new API was introduced - tvg::Saver::save.
