Event transformations for higher level events

[lucidd]

Idea

The basic idea is to have some kind of stream of input events that can be transformed. With that it would be possible to transfrom a stream of raw low level events like button pressed or mouse moved to higher level events like double click or mouse dragged.

Transformations should be able to:

• Emit new events
• Omit old Events
• Passthrough old Events

  Use cases

• Key Sequences (Konami Code)
• Key Combination (Ctrl-C)
• Drag Event
• Double Click / Tap Events
• Touch / Mouse Gesture Events

It could also potentaly used to solve #11

You could also go as far as implementing an application specific transformation that transforms raw or higher level events to application specific events like Move or Attack.

raw touch events => swipe gesture event => Attack Event

Implementation

I don't think it is possible to implement something like that with the current design since you cant extend the Events. I think #30 with the Event trait should help with this.

Open Questions

• Interaction with the Gameloop
• Interaction with the Backend (SDL2)

  References

• Dart Event Streams onKeyPress
• Dart StreamTransfromer
• Spec for Reactive Streams

[bvssvni]

Good idea! @Denommus Is also looking into FRP.

Are you on IRC (#rust-gamedev) sometimes?

[lucidd]

yeah im usually on IRC in #rust and #rust-gamedev. Its good to know that im not the only one looking into this stuff :smile:

[bvssvni]

I am thinking about this as well. Perhaps we could do something like this:

// Triggers on double click of left mouse button.
let mut dc = Event::new().double_click(mouse::Left).once();
...
for e in ... {
    if dc.trigger(&e) {
        // Handle event.
        ...
        // Resets event so it can trigger again.
        dc.reset();
    }
}

This is similar to the current design in rust-event, but without a "event center" and much more simplified. I wonder if we could use a nested type structure like iterators in Rust, for example Once<T> which stores a flag whether it triggered. Methods can propagate to the wrapper type by using traits. For key mapping we can use Box<Trigger>, to store in struct members to control player actions, and pass in the event through a method on the controller, like we do in FirstPerson in Piston. Other traits can be added for AbsoluteAxis and RelativeAxis etc.

[bvssvni]

@Coeuvre What do you think about this design?

[Denommus]

I'm probably basing myself mostly on signal function FRP, which is talked about in this paper: https://dl.dropboxusercontent.com/u/23124877/FRP/20103_amsden_istudy.pdf

[bvssvni]

It is possible to use ai_behavior to something like this.

Any this is outside the scope of this library, so I'll close this.