DXT -> BCN?

[Josh015]

I was just wondering if it would be a good idea to switch from Dxt* naming scheme to Bcn* in order to match Microsoft? Also, are there any plans to support BC4 and BC5 since L8 and La8 would map well to them?

[fintelia]

My preference would be to create a new image-bcn crate and move all the dxt encoding/decoding to there. We could then deprecate and eventually remove all the Dxt* code from image and retain only support for the DDS format.

I don't personally have plans to add support for other block compression formats, but PRs are welcome!

[HeroicKatora]

Starting the revision from a clean slate in a new crate sounds preferrable for me as well. Note it's possible retro-fit the current implementation to instead use a crate. The only implementation that we (sadly) can't readily change is the DXTVariant enum as it wasn't defined to be non-exhaustive (quite an oversight tbh). But we could add a new enum instead and provide a converter from the old. That should leave many, if not all, interfaces intact. The DdsEncoder is entirely opaque as well. We can additionally define type aliases to rename everything to the Bcn* names, also without any major breakage (sadly we can't do the same for enum variants).

A new crate could expose many more internals, as long as it's not a public dependency of image the need for a stable interface isn't as large. It could experiment a lot more as well. At some point when format support gets detailed enough, we move them out into separate crates. For example, this happened with png, gif, tiff.

[Waelwindows]

I think it's better to map BC5 to R8G8, because not all textures use the "green" channel as alpha. e.g. normal maps

[fintelia]

@Waelwindows thanks for catching that! It probably isn't worth adding R8G8 as a format just to handle BC5, given that for decoder output La8 actually just means "a two channel format where even bytes are one channel and odd bytes the other". But you are right that the documentation should say that clearly somewhere so that users don't get confused