Support for WebP is imperfect: Alpha, Lossless and Animation isn't supported

[fralonra]

Hi, all.

I noticed that the support for WebP is not all done.
See

image/src/codecs/webp/decoder.rs

Line 101 in 702c1e7

b"ALPH" | b"VP8L" | b"ANIM" | b"ANMF" => {

The comment below says: Alpha, Lossless and Animation isn't supported.

I dont know why not to support them and is there a plan to make them work?

[installgentoo]

I had to do

			if let image::ImageFormat::WebP = fmt {
				// TODO CARGO.toml throw away libwebp_image when image gets colour info in webp
				Res(libwebp_image::webp_load(img.into_inner()))?
			} else {
				img.decode().map_err(|_| "Cannot decode image")?
			}

some time back. libwebp_image was created 3 years back, so i wouldn't expect first-class webp support any time soon.

[fintelia]

The main issue here is that image doesn't like to depend on libraries not written in Rust. Since libwebp is written in C, we rely on a (currently incomplete) re-implementation of it in Rust. The changes in #1536 and #1549 will be included in the next release and do improve the situation, but there is still more left.

[installgentoo]

@fintelia why does image state YES for webp support, when i still get
Cannot decode image: Unsupported(UnsupportedError { format: Exact(WebP), kind: GenericFeature("ALPH") })
?

[fintelia]

This was fixed in #1685