Expose GoogleMaps iOS SDK icon property to improve Marker rendering performance

[victormartingarcia]

Does any other open PR do the same thing?

This PR is based on #1491 changeset

It hasn't been merged (presumably unsolved conflicts), but I see Marker tracksViewChange property is already exposed on master branch, so it makes sense to expose Marker icon property as well

What issue is this PR fixing?

Rendering Markers on iOS using Google Maps have some performance issues (see #2616, #1031, #2575 ..)
Some people have solved that with some extra logic tweaking tracksViewChange property (see #1031 (comment) ), but as Google explains in the SDK docs, for static Markers is much better to use icon property.

Using this icon property solves all iOS performance issues, making the map much smoother :)

How did you test this PR?

This fix has been tested on iPhone simulator and real devices (iPhone 6 and iPhone X) with extremely good results.

On Android, icon property works like image property, as Android SDK does not differentiate between static image Markers and View-based ones

Example

<Marker
    coordinate={{
        latitude: this.state.myLatitude,
        longitude: this.state.myLongitude
    }}
    icon={require('../Images/myIcon.png')}
/>

[rborn]

Thanks for the PR ❤️

I wonder of we could unify the icon/image props between the platforms? so we use one name only? Or on iOS we can use both image and icon ?

@alvelig thoughts ? and 🐽
LGTM

[victormartingarcia]

@rborn on iOS you can use both image and icon for different purposes (icon only works for static images)

Let me check if I can make it compatible with android, for not having to differentiate it on Marker props

[victormartingarcia]

I managed to support icon property on android as well, so no need to differentiate platform on Marker definition ;)

Using icon on android is exactly the same as using image, as android Google Maps SDK does not differentiate between static image Markers and View-based ones

[rborn]

@victormartingarcia looks good, thanks.
One question though: is there anything we need to do to handle @2x/@3x images? How do the marker decide the size of the icon? (maybe we should add some docs saying what's the ideal marker icon size if google specifies something about it?)

[victormartingarcia]

One question though: is there anything we need to do to handle @2x/@3x images?

I've tested and @2x/@3x images are handled automatically 👍

How do the marker decide the size of the icon?

Just like with image, using this icon property shows a Marker with the same size as the source picture.

(maybe we should add some docs saying what's the ideal marker icon size if google specifies something about it?)

Haven't found anything about Marker size in Google Maps SDKs docs...

[rborn]

@victormartingarcia let's wait a little for @alvelig to reply (if) and then we'll merge 🎉

[christopherdro]

Related to #1491

[christopherdro]

I'm not sure why this wasn't caught in the tests that ran on this PR but I am following up with the following #2651