# libcaesium
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Libcaesium is a simple library performing JPEG, PNG, WebP and GIF (experimental) compression/optimization written in
Rust, with a C interface.
> [!WARNING]
> starting from v0.6.0 the library is written in Rust and no longer in C. There's a C interface, but it's not backward
> compatible with the <0.6.0.
## Usage example
Libcaesium exposes two functions, auto-detecting the input file type
```Rust
use caesium::parameters::CSParameters;
use caesium::compress;
let mut parameters = CSParameters::new();
parameters.keep_metadata = true;
parameters.jpeg.quality = 60;
let success = compress(input, output, ¶meters).is_ok();
```
## Compilation
Compilation is available for all supported platforms: Windows, macOS and Linux.
> [!NOTE]
> if you don't use the `--release` flag, the PNG optimizations can take a very long time to complete, especially
> using the zopfli algorithm.
>
```bash
cargo build --release
```
The result will be a dynamic library usable by external applications through its C interface.
## Usage in C
*You can find the C header file in the include folder in the project root directory.*
Libcaesium exposes there C functions, auto-detecting the input file type:
### Based on quality values
```Rust
pub unsafe extern "C" fn c_compress(
input_path: *const c_char,
output_path: *const c_char,
params: CCSParameters
) -> CCSResult
```
#### Parameters
- `input_path` - input file path (full filename)
- `output_path` - output file path (full filename)
- `parameters` - options struct, containing compression parameters (see below)
#### Return
A `CCSResult` struct
```Rust
#[repr(C)]
pub struct CCSResult {
pub success: bool,
pub code: u32,
pub error_message: *const c_char,
}
```
If `success` is `true` the compression process ended successfully and `error_message` will be empty.
On failure, the `error_message` will be filled with a string containing a brief explanation of the error.
### Based on output size
```Rust
pub unsafe extern "C" fn c_compress_to_size(
input_path: *const c_char,
output_path: *const c_char,
params: CCSParameters,
max_output_size: usize,
return_smallest: bool,
) -> CCSResult
```
#### Parameters
- `input_path` - input file path (full filename)
- `output_path` - output file path (full filename)
- `parameters` - options struct, containing compression parameters (see below)
- `max_output_size` - the maximum output size, in bytes
- `return_smallest` - whether to return the smallest
#### Return
A `CCSResult` struct
```Rust
#[repr(C)]
pub struct CCSResult {
pub success: bool,
pub code: u32,
pub error_message: *const c_char,
}
```
If `success` is `true` the compression process ended successfully and `error_message` will be empty.
On failure, the `error_message` will be filled with a string containing a brief explanation of the error.
### Based on convert output
```Rust
pub unsafe extern "C" fn c_convert(
input_path: *const c_char,
output_path: *const c_char,
format: SupportedFileTypes,
params: CCSParameters,
) -> CCSResult
```
#### Parameters
- `input_path` - input file path (full filename)
- `output_path` - output file path (full filename)
- `format` - target image format (see below)
- `parameters` - options struct, containing compression parameters (see below)
#### Return
A `CCSResult` struct
```Rust
#[repr(C)]
pub struct CCSResult {
pub success: bool,
pub code: u32,
pub error_message: *const c_char,
}
```
If `success` is `true` the compression process ended successfully and `error_message` will be empty.
On failure, the `error_message` will be filled with a string containing a brief explanation of the error.
### Compression options
The C options struct is slightly different from the Rust one:
```Rust
#[repr(C)]
pub struct CCSParameters {
pub keep_metadata: bool,
pub jpeg_quality: u32,
pub jpeg_chroma_subsampling: u32,
pub jpeg_progressive: bool,
pub png_quality: u32,
pub png_optimization_level: u32,
pub png_force_zopfli: bool,
pub gif_quality: u32,
pub webp_quality: u32,
pub tiff_compression: u32,
pub tiff_deflate_level: u32,
pub optimize: bool,
pub width: u32,
pub height: u32,
}
```
The option description is the same as the Rust counterpart.
Valid values for `jpeg_chroma_subsampling` are `[444, 422, 420, 411]`. Any other value will be ignored and will be used
the default option.
Valid values for `tiff_compression` are `[0 (Uncompressed), 1 (Lzw), 2 (Deflate), 3 (Packbits)]`. Any other value will
be ignored and `0` will be used.
Valid values for `tiff_deflate_level` are `[1 (Fast), 6 (Balanced), 9 (Best)]`. Any other value will be ignored and
`Best`
will be used.
### Supported file types
```rust
#[repr(C)]
#[derive(PartialEq, Eq, Clone, Copy)]
pub enum SupportedFileTypes {
Jpeg,
Png,
Gif,
WebP,
Tiff,
Unkn,
}
```
## Compression vs Optimization
JPEG is a lossy format: that means you will always lose some information after each compression. So, compressing a file
with 100 quality for 10 times will result in an always different image, even though you can't really see the difference.
Libcaesium also supports optimization. This performs a lossless process, resulting in the
same exact image, but with a smaller size (10-12% usually).
GIF optimization is possible, but currently not supported.
WebP's optimization is also possible, but it will probably result in a bigger output file as it's well suited to
losslessly convert from PNG or JPEG.