Make alpha its own property in the styling language

[lilleyse]

Would it be worthwhile to add an "alpha" property? This would give more flexibility for complex styles where the alpha is treated differently than color.

One example: color by groups but set alpha to be smooth.

{
    "color": {
        "conditions": [
            ["${height} < 100", "color('red')"],
            ["${height} < 200", "color('green')"],
            ["${height} < 300", "color('blue')"],
            ["true", "color('yellow')"]
        ]
    },
    "alpha": "mix(0.0, 1.0, min(${height} / 300, 1.0))"
}

[likangning93]

how Iron Man could we Iron Man?

[pjcozzi]

I thought about doing this at one point - I might have even done it in the first prototype, but there's no discussion in #2. @ggetz do you recall?

@lilleyse concretely, what do you propose:

color : rgb
alpha : a

or

color : rgba
alpha : a // overrides color.a

or something else?

[ggetz]

I think there was some brief discussion, but it was put on the back burner since transparency could be accomplished with rgba. I see no reason why not, css has it's own opacity property in addition to rgba.

[lilleyse]

I would prefer the override method.

[pjcozzi]

Override is OK with me.

Could be scoped 1.0 or post 1.0.

[pjcozzi]

Since this can be done in a backwards compatible way, pushing post 1.0.

[lilleyse]

Noted in #2 (comment)