JEP 253 webrev ready for review

Michael Ennen mike.ennen at
Fri Sep 4 05:17:14 UTC 2015

I am trying to mentally digest the CSS API, but I am having trouble
answering the question of whether or not the following scenario is now
possible (using only public APIs). Imagine one wanted to create a new class
that was analogous to, and that it worked "all
the way down" in terms of being parsed from CSS into a
StyleableProperty<Color>. For concreteness, say one wanted to implement a
fadein function:

fadein( <color> , <number>% )

The fadein function takes a color and computes a more opaque version of
that color.
The second parameter is the opacity, ranging from 0% to 100%. Has no effect
fully opaque colors.

Does the API allow for a way to hook this new function up into the CSS
parser? If one implemented FadeInColorConverter extends
StyleConverter<ParsedValue[], Color> that worked according to the above
specs, how would one hook this fadein function into the parser, so that one
can write CSS such as:

my-awesome-color: fadein(my-semi-transparent-color, 30%);

and have a StyleableObjectProperty<Color> come out the other side?

If this is possible using the new APIs, then this makes those APIs very
powerful in terms of the possibilities of extending the built-in CSS
capabilities in very powerful and interesting ways. If it is not possible,
would it be feasible to make it so in the scope of this JEP?

Thanks very much,
Michael Ennen

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