[Suggestion] WebP Encoding Support

[liftoff]

The crate currently supports WebP decoding but it would be nice if it also supported encoding as well. I'd definitely take advantage of it in one of my forthcoming projects.

[liftoff]

For reference purposes (in case anyone wants to know how to encode WebP in the mean time), here's how to encode an ImageBuffer to WebP via libwebp/libc:

extern crate libc;
use libc::{c_int, c_float, size_t};
use std::io::{Write, BufWriter};
use std::fs::File;
use std::path::Path;

#[link(name = "webp")]
extern {
// Here's the C lib's function def:
//     size_t WebPEncodeRGB(const uint8_t* rgb, int width, int height, int stride, float quality_factor, uint8_t** output);
//     size_t WebPEncodeLosslessRGB(const uint8_t* rgb, int width, int height, int stride, uint8_t** output);

    fn WebPEncodeRGB(rgb: *const u8, width: c_int, height: c_int, stride: c_int, quality_factor: c_float, output: *mut *mut u8) -> size_t;
    fn WebPEncodeLosslessRGB(rgb: *const u8, width: c_int, height: c_int, stride: c_int, output: *mut *mut u8) -> size_t;
    fn WebPFree(ptr: *const u8);
}

let filetype = "webp";
let ref path_str = format!("/tmp/test.{}", filetype);
let path = &Path::new(path_str);
// Pretend this screenshot() function returns ImageBuffer<Rgb<u8>, Vec<u8>>:
let img = screenshot();
let stride = width * 3;
let lossless = false; // Set to true for lossless (Warning: CPU intensive/slow)
let quality: c_float = 75.0; // Quality level of the WebP image
let mut output: *mut u8 = std::ptr::null_mut();
let raw = img.clone().into_raw();
unsafe {
    let length: usize;
    if lossless {
        length = WebPEncodeLosslessRGB(raw.as_ptr(), width as c_int, height as c_int, stride as c_int, &mut output);
    } else {
        length = WebPEncodeRGB(raw.as_ptr(), width as c_int, height as c_int, stride as c_int, quality, &mut output);
    }
    let mut fout = BufWriter::new(File::create(&path).unwrap());
    let slice = std::slice::from_raw_parts(output, length);
    let _ = fout.write_all(slice).unwrap();
    let _ = fout.flush();
    let _ = WebPFree(output); // IMPORTANT: Make sure we free that memory
}

[emirror-de]

Hi there,

the webp crate contains the possibility to encode. It already uses DynamicImage as input struct. Maybe it would be an idea to integrate this (or take this implementation as reference) to support enconding?
There exists also the libwebp crate that contains the bindings.

[kruserr]

Any progress on this?
Would love to see this added!

[fintelia]

Hm, I don't think there's been any progress on a pure Rust WebP encoder, but the webp crate linked above looks like a viable option if you want a safe wrapper for the FFI bindings in libwebp-sys.

[Sparkenstein]

Awesome 🎉
Thanks for the encoding support, when can we expect next release?