JS Interop: Direct Access to "draw()"?

[elm-community]

JS Interop: Direct Access to "draw()"?

[w0rm]

@felixguendling why do you want to move the canvas element, and not the triangle within it? You could've sent the offset to webgl and use it to offset the triangle.

[w0rm]

@felixguendling, sorry. I see why you need it now, it is moved with the main map and you have to reposition it with the opposite offset.

[felixguendling]

@w0rm thank you for looking into the problem.

Yes. That's the approach other implementations use, too. This way, I don't have to use the "move" callback commented out in the file: https://github.com/felixguendling/elm-map/blob/master/index.html#L24

If I use the "move" callback (and position the canvas outside, not as child DOM of the map), another undesired "effect" appears: the constant rerender is not exactly synchronous with the drag movement of the user. Thus, the triangle is not at the same geographical location which looks weird. Furthermore, the system load increases significantly when dragging the map around (laptop fan makes noise).

I think this is a problem with Elm Ports being asynchronous in general, making real-time JS interop hard. But perhaps there is a way to solve this specific problem without touching the Elm compiler?

Edit: I thought about implementing a simple tile-based map in Elm (which would result in synchronous updates!). But I think that's not an easy problem. So using an existing mature library like Leaflet was my first approach.

[nphollon]

This seems like a great topic to bring up on the elm-dev mailing list.

As for finding a work-around within elm-webgl, I don't see a good way of doing it. You'd have to decouple from Elm's VDOM render loop somehow, right?

[felixguendling]

Thanks for the hint. I opened a discussion:
https://groups.google.com/forum/#!topic/elm-dev/lAEnpHQzS5c