Add visible attribute to GeoJSON layer

[davidbrochart]

Fixes #827.

[giswqs]

Wow, this is nice! I have been waiting for this feature for a while. Thank you.

[giswqs]

Besides the visible attribute, would it be possible to also add an opacity attribute like the TileLayer?

[davidbrochart]

I've been trying to implement the visible attribute using opacity and fillOpacity before reaching this solution. My conclusion is that it was a mess, because there are global opacities and feature opacities, and once you set the global opacity to 0 you cannot revert.

[giswqs]

Thanks for clarifying. It would still be nice if you can add the fillOpacity attribute. This will allow the fill opacity of polygon layers to be changed interactively.

[davidbrochart]

Yes, but it can get quite complex because you need to handle the opacity also (polygon border, which can have a different value than fillOpacity), and the style in mouseover and mouseout can also set the opacity...
Would you like to try in a separate PR?

[giswqs]

I would love to contribute. I really need to learn JavaScript. Once this PR is merged and the visible attribute is working, I will see if I can make the opacity attribute work.

[jasongrout]

The docs test is failing for unrelated reasons (404 on a resource)

[giswqs]

I just tested v0.17.0 and the GeoJSON visible attribute. Just figured out that you can actually control the style attribute to set opacity. So it is now possible to change the GeoJSON layer opacity interactively.

g.style={'fillOpacity': 0.5, 'opacity': 1}

[davidbrochart]

So this is not working since v0.17, right? I guess it was already working before.

[giswqs]

@davidbrochart It is working well. I was just saying that the geojson layer opacity can be changed using the style attribute, so I don't need to submit a PR to mess up the JS code.

[giswqs]

I did not know that style attribute before v0.17.0. I was working on the PR and then realized that the style attribute is exactly what I needed to change layer opacity interactively, so no PR from me.

[davidbrochart]

Great, I just meant that this is not particularly true since v0.17, the style attribute was there before.