Touch module in Elm 0.17

[Tobias Hermann]

Hi,

I'm currently trying to update some of my old elm code to version 0.17. I see that Mouse and Keyboard were moved to separate packages, but I can not find anything touch related. Can the touch functionality still be found somewhere?

Tobias

[Janis Voigtländer]

Touch support is gone for now.

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[Joey Eremondi]

In principle, could you do touch support with Ports?

Support for anything is never truly gone with ports!

[Janis Voigtländer]

True, but I don't think that was the question. 

[Tobias Hermann]

OK, thanks guys. I will consider using ports for this. But perhaps I will abandon some projects completely. This one for example is around since Elm 0.10 and very far away from current best practice. :D

[Tobias Hermann]

I decided to update my old projects. It was a relatively big change to switch from signals to the Elm architecture, but I learned a lot and the code became easier to understand. But now I am back to my touch question. :D

Is there a specific reason the functionality is no longer available? I would think it is not that different from the mouse stuff, or is it?

[Glen Mailer]

If you skim over the code in the new mouse module, you'll see there's not a huge amount there.

You can probably write some very similar code using the "on" function in Html.Events with a custom decoder.

This has to be applied to an HTML element rather than being global, but if you pick something near the top of your tree you should get a similar effect

Hope that helps!
Glen

[Tobias Hermann]

Thanks. I now can get messages for a touchstart on a specific element if I use Json.Decode.succeed to produce a fixed message. Additionally I would like to get the pixel coordinates for the touches. Any ideas on how the decoder for this could look like?

[Steve Schafer]

That's like saying Elm supports everything, as long as you define "dropping out to JavaScript" as "part of Elm."

[art yerkes]

I do it like this:

D.oneOf [
	D.at ["touches", "0"] (D.object2 TouchPosition ("pageX" := D.float) ("pageY" := D.float))
	, D.object2 TouchPosition ("pageX" := D.float) ("pageY" := D.float) ]

Which can be bound to both touch and mouse events and yields whatever the event has.

[Tobias Hermann]

Thank you very much. It works.

In case anybody is interested, here is the full minimal example using the snippet: https://gist.github.com/Dobiasd/5aba6bbf872301977bc35790a04bfde0

[John Bugner]

May I ask why touch support disappeared? Was it hard to convert to using subscriptions or something?

(Sorry for bumping an 2-month-old thread, if I'm not supposed to do that.)

[Janis Voigtländer]

I don’t think there was a technical reason or specific complication. The Touch module had simply never been really finished API-wise, and during the transition from Elm 0.16 to 0.17 there was no priority to polish touch support in particular. So while stuff like Keyboard and Mouse and Graphics was taken out of core, but preserved with some modifications (mainly signals vs. subscriptions) in separate packages, Touch was dropped for the moment. I guess because it’s much less clear for it than for the other three mentioned modules what the “final” API will look like. (All that is just my inference from discussion traffic, I wasn’t privy to the decisions being made then and there.)

​

[Rex van der Spuy]

On Tuesday, July 26, 2016 at 1:35:07 PM UTC-4, Janis Voigtländer wrote:

 I guess because it’s much less clear for it than for the other three mentioned modules what the “final” API will look like.

 Would it make sense to combine both mouse and touch into a single `pointer` object?

[OvermindDL1]

As long as you have multiple pointer objects.

Linux supports multiple simultaneous mice (no clue if browsers do) so there is precedent there.  And touch's are basically multiple mice (although some interfaces expose a 'strength' or 'pressure' or so too to say how hard the person is touching).  Could easily be combined.

[art yerkes]

A proper expression of touch includes multiple touches that can come and go independently, along with extra parameters for each (pressure is one but velocity is another too).  Neither was relevant to the things I was writing but it'd be awesome to see a touch API that exposes touch fully in a way that doesn't get weighed down with model state or require too much boilerplate.

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