Duotone support.

[Lattyware]

Initial work in #1, but split out here as the implementation changes were bigger.

As of 47a4483, this is in and working (bumps to 4.0.0 as it requires a change to the shape of Icon to support multiple paths).

Here shown rendering in a modified version of elm-fontawesome-example.

duotone =
    exampleSection "Duotone"
        [ Html.div [ Icon.fa3x ]
            [ Duotone.camera |> Icon.viewIcon
            , Duotone.camera |> Icon.viewStyled [ Icon.swapOpacity ]
            , Duotone.fireAlt |> Icon.viewIcon
            , Duotone.fireAlt |> Icon.viewStyled [ Icon.swapOpacity ]
            , Duotone.busAlt |> Icon.viewIcon
            , Duotone.busAlt |> Icon.viewStyled [ Icon.swapOpacity ]
            ]
        , Html.div [ Icon.fa3x ] duotoneOpacity
        , Html.div [ Icon.fa3x ]
            [ Duotone.crow |> Icon.viewStyled [ HtmlA.attribute "style" "--fa-secondary-opacity: 1.0; --fa-primary-color: dodgerblue; --fa-secondary-color: gold;" ] ]
        ]


duotoneOpacity =
    [ 0.2, 0.4, 0.6, 0.8, 1 ] |> List.map (\o -> Duotone.busAlt |> Icon.viewStyled [ opacity "secondary" o ])


opacity path o =
    HtmlA.attribute "style" ("--fa-" ++ path ++ "-opacity: " ++ String.fromFloat o)

There are a couple of issues here. The core one is the lack of custom property support in Elm. The expected HtmlA.style "--fa-primary-opacity" "0.5", for example, doesn't work. This is tracked in this upstream issue. You can work around this, as shown, but this is very fragile and will override any other styles making it very hard to combine. Ideally we would expose helpers in the Styles module for this, but until we can do it properly it isn't worth it.

Second, as this is a pro-only feature, we can't actually give examples as we only have the free version publicly built, so pro users will have to try it out for themselves.

[Lattyware]

For now, I'm not going to bother releasing a new version of the library—pro users can build using master anyway, and free users gain nothing from this version. I'd also prefer to have the custom property issue fixed before releasing if possible.

[Lattyware]

As this is a pro feature, it is no longer supported due to a lack of support from FontAwesome.