Pre-load all images

[themakshter]

Instead of returning promises, which seems a bit more complicated, it might be easier and better to pre-load the images at the beginning. This will mean going over the map object we receive and creating an array of promises. Once all of them have been resolved, we can then draw images without worrying about anything.

[themakshter]

This is not urgent, but still adding some resources:

Although we switched to using snap.svg it has a load function which can be used to load the images.

Snap.load
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