CSS Color functions

[Michael Strauß]

I don't think it makes a lot of sense to add even more non-standard
functions to JavaFX CSS. Instead we should work towards bringing our
implementation closer to the web standard.
You wrote that it might not be worth to wait for the standard; does
that mean that you'd get a lot of value from this proposed feature?
Improving one line of code in Modena.css is probably not enough justification.

On Sun, Jan 15, 2023 at 1:31 AM Scott Palmer <swpalmer at gmail.com> wrote:
>
> I was looking at Modena.css and came across this:
>
>     /* A bright blue for the focus indicator of objects. Typically used as the
>      * first color in -fx-background-color for the "focused" pseudo-class. Also
>      * typically used with insets of -1.4 to provide a glowing effect.
>      */
>     -fx-focus-color: #039ED3;
>     -fx-faint-focus-color: #039ED322;
>
> I noticed two things pertaining to -fx-faint-focus-color.  Although I've used this form to specify colors myself, the JavaFX CSS Reference Guide at https://openjfx.io/javadoc/19/javafx.graphics/javafx/scene/doc-files/cssref.html#typecolor does not mention being able to use an 8-digit form of #rrggbbaa when using hex digits. Only the 3- and 6-digit forms of hexadecimal RGB are mentioned. RGB + Alpha colors are only documented in the form of rgba(#,#,#,#) and rgba(#%,#%,#%,#).
>
> More importantly, this is a copy of -fx-focus-color with an added alpha channel, but it's created by repeating the literal color value and appending the alpha component, rather than somehow deriving it from -fx-focus-color.  Similar repetition is needed for the semi-transparent chart colors.
>
> Would it make sense to add support for something similar to derive( <color> , <number>% ) to specify a color based on an existing color with a new value for the alpha channel (or any other) value? Maybe a color-transform method that would do for an RGBA color vector what other transforms do for spatial coordinates?*
>
> Regards,
>
> Scott
>
> * Note: It seems future CSS standards are looking for ways to do similar things.  A color-mod function was proposed in https://www.w3.org/TR/2016/WD-css-color-4-20160705/#funcdef-color-mod but removed in the next revision https://www.w3.org/TR/2022/CRD-css-color-4-20221101/#changes-from-20160705.  I'm not following CSS development closely, but some googling suggests the next proposal is based on a new keyword 'from' to create derived colors.  E.g rgb(from skyblue, 255 g b) to get a color based on skyblue with a red component of 255.  This is mentioned here https://github.com/w3c/csswg-drafts/issues/3187#issuecomment-499126198  I'm skeptical that it is worth waiting for the dust to settle on the CSS standard, but supporting whatever they come up with is a possibility.
>