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Re: [fxtf-drafts] [filter-effects] Why can't opacity() filter function ever increase opacity?

From: Amelia Bellamy-Royds via GitHub <sysbot+gh@w3.org>
Date: Wed, 24 Jan 2018 18:13:21 +0000
To: public-fxtf-archive@w3.org
Message-ID: <issue_comment.created-360224183-1516817600-sysbot+gh@w3.org>
> as a multiplicative alpha effect

Technically, what I'm asking for would still be a multiplicative alpha effect. Just allowing multiplication with values greater than 1. 😉

`opacity()` as currently defined has very few use cases in the `filter` property, since there's nothing it can do that the `opacity` property can't.  I've seen it [used as part of workarounds for broken supports testing](https://codepen.io/tigt/post/blurred-background-image-with-fallback), that's all. It would have some use in the image filter function (if anyone implemented that).

I agree that adding any other behavior (e.g., additive offsets) would be something to defer to another level of the spec.

The problem with defering `opacity(150%)` to a future spec is that, as it is currently spec'd, that is a valid declaration. The parser accepts it. It just doesn't have any effect different from `opacity(100%)`. So changing later becomes a compat risk.

(Maybe it's already a compat risk, I don't know. People could be doing weird things with `calc` and variables, confident that if the result is at least 100% then the filter won't change anything.)

Adding this functionality in the future would require adding a separate function (`alpha()`, maybe), that has the full functionality that `opacity()` should have had.

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Received on Wednesday, 24 January 2018 18:13:23 UTC

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