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Re: [csswg-drafts] [css-color-adjust-1] background-color in forced color modes needs more than a simple unset (#4175)

From: CSS Meeting Bot via GitHub <sysbot+gh@w3.org>
Date: Wed, 21 Aug 2019 16:45:46 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-523545605-1566405945-sysbot+gh@w3.org>
The CSS Working Group just discussed `background-color in forced color modes needs more than a simple unset`, and agreed to the following:

* `RESOLVED: background-color computes to the system background-color for all values but heh alpha channel`

<details><summary>The full IRC log of that discussion</summary>
&lt;dael> Topic: background-color in forced color modes needs more than a simple unset<br>
&lt;dael> github: https://github.com/w3c/csswg-drafts/issues/4175<br>
&lt;dael> Rossen_: I'll take it since melanierichards is on vacation<br>
&lt;dael> astearns: How much time do you need?<br>
&lt;dael> Rossen_: Quick.<br>
&lt;Rossen_> https://www.w3.org/TR/css-color-adjust-1/#forced-colors-properties<br>
&lt;dael> Rossen_: When the forced color behavior was desc in the link^<br>
&lt;dael> Rossen_: These are the properties overwritten by system colors. Fallback was spec that every property that has no overrides gets the revert !important which means revert to original UA stylehseet which for bg color is transparent<br>
&lt;dael> Rossen_: Not expected. All other colors reverting makes sense. Background being reverted to ransparent you lose all non-transparent. Intended it go to system bg color<br>
&lt;dael> Rossen_: Idea from fantasai was can re do something to transparent color and see if computes to self similar to currentColor. Not really the same. Transparent color is a named color.<br>
&lt;aja> re: forced-colors, should transparent (borders-color only?) be allowed in addition to the non-deprecated system colors? will file issue if it sounds reasonable.<br>
&lt;dael> Rossen_: If we spec transparent computes to itself as computed we're making an exception for one named color. Think it's a bit wierd. crrentColor is an instruction to cascade algo to go back to a value. Not really the same<br>
&lt;dael> Rossen_: Ask here is that we take bg color out of the list and spec the behavior that it falls back to system bg color in case of forced colors<br>
&lt;dael> Rossen_: That was intended impl that we had to back out when making code according to spec<br>
&lt;dael> AmeliaBR: This would need to be defined in prose b/c incvolves a switch on computed value we can't define in cascade.<br>
&lt;dael> Rossen_: Yes<br>
&lt;dael> AmeliaBR: Would it work to force all bg to be opaque?<br>
&lt;dael> Rossen_: Inverse problem which would be jsut as bad<br>
&lt;dael> AmeliaBR: Okay.<br>
&lt;dael> AmeliaBR: It really has to be done with a little magic ans special prose<br>
&lt;dael> Rossen_: Magic is simple. When you compute value of bg color for non-transparent the value is computed to the system bg color.<br>
&lt;dael> Rossen_: To your observation AmeliaBR the explanation will be bg color only.<br>
&lt;dael> AmeliaBR: Any interaction with bg image? bg image the current proposal is keep the image and use backplate behind text to add contrast. Would you do them separately?<br>
&lt;dael> Rossen_: What you said is right for bg image. For bg color if the color is non-transparent it will be system bg color. So if you draw a backplate it would be non-observable visually or object model. Somewhat wasteful to render.<br>
&lt;dael> Rossen_: Otherwise for bg image the backplate takes effect and guar. forground in desired contrast<br>
&lt;dael> dbaron: Is this the right treatment for bg colors with alpha between transparent and opaque. alternative is don't touch alpha and change color compontents to system color<br>
&lt;dael> Rossen_: valid point. There's a different issue that addresses what you desribed when talking about interpolation. It will end up interpolating most of alpha channel. I like your proposal<br>
&lt;dael> astearns: Summary Rossen_ ?<br>
&lt;dael> Rossen_: Prop: background-color computes to the system background-color for all values but hte alpha channel<br>
&lt;dael> astearns: Can we resolve on this?<br>
&lt;dael> astearns: Objections?<br>
&lt;dael> RESOLVED: background-color computes to the system background-color for all values but heh alpha channel<br>
&lt;dael> s/heh/the<br>

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Received on Wednesday, 21 August 2019 16:45:48 UTC

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