Add missing map2/apply2 functions to Pixel trait

[jnickg]

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This PR merges quick changes to add a few missing functions to Pixel so that basic image math operations are easier when dealing with alpha-channel images.

Commit Messages

• Account for alpha channel to simplify some image math operations where naively operating on all pixel components won't work (such as summing images, where usually picking one alpha value from self or other makes more sense)

[HeroicKatora]

The {apply,map}2_with_alpha are well-defined extensions and were sketched out already. Overall whether or not they can be accomplished with the existing functions or not wouldn't matter too much here, it's a pretty small change whose minor breakage can be easily part of the next major version. (In theory there could be an approximate default impl based on as_channels and color model but I don't think the risk of modelling error is worth it to mitigate that inconvenience).

I think the opposite applies to *_without_alpha. Those can be written by using a specific parameter choice for g from the with_alpha version: |lhs, _| lhs. We don't have the equivalent method for the single pixel function either. Here it might be best to provide them as defaults on the trait instead.

[jnickg]

Hi @HeroicKatora , thanks for the review. I might be misunderstanding something though, can you please clarify? I see these functions which look like the equivalent single-pixel functions, which is why I added them. I'm happy to elide *2_without_alpha functions though (in fact I only added them for parity, and also thought they could just use the closure you mentioned).

Just to clarify, it sounds like you're looking for a code change for the *2_without_alpha functions so that they are defaults on the trait. Is that accurate? Would you like the *2_with_alpha functions implemented that way as well?

Thanks!

[HeroicKatora]

Just to clarify, it sounds like you're looking for a code change for the *2_without_alpha functions so that they are defaults on the trait. Is that accurate? Would you like the *2_with_alpha functions implemented that way as well?

Yes, I meant these functions aren't present on the impl block in color.rs. It looks like they are defaulted in precisely the manner which I had thought the {map,apply}2_without_alpha should be. This is definitely good enough. There's no need to default *2_with_alpha.

[HeroicKatora]

LGTM, it fits the design. Should be considered for the next breaking version change (0.26).

[jnickg]

Just to close the loop, I rebased onto the latest main and applied the cargo fmt changes to make CI happy. Hopefully that is enough to get it merge-able

[jnickg]

@HeroicKatora looks like everything is green, but I don't have a "merge" button and can't push a merge commit. Please let me know if there's any further action I should take.

[HeroicKatora]

This is still a breaking change so in light of the issue with packaging, a release of 0.25.2 before this is merged to the main branch for 0.26 then. But should be good to go, nothing more to do from your side I think.

[jnickg]

Thank you!!!

[ripytide]

I think we should wait to merge this until the the conflict with #2259 has been discussed.