Clickable area according to bitmap

[nbrr]

Example draft for #22: it displays the cone pine image and moves it randomly when one tapes on the non-transparent area. Swipe exits. I did it quick & dirty as an example to see how it works out, it needs be abstracted.

Also relevant to #21: indeed we can just use the move semantics; I also had in my mind that maybe one could want to manipulate the universe outside the callback but the way it is now is not limiting and I can't come up with a scenario interesting enough for now.

Also relevant to #18: introduced a couple of fixes to panics introduced by the switch to u32 pixels.

[nbrr]

Throwing in ideas for abstraction.

trait InteractiveObject<T> {
    fn try_activate(&self, swipe: Swipe) -> bool;

    fn action(???) -> T;

    fn render(&self, canvas: &mut Canvas);
}

struct SimpleTappableObject{
    width: usize,
    height: usize,
    /// Where the object is meant to be placed
    origin: (usize, usize),
    /// Interactive points
    bmap: BlitMap,
    /// Visual rendering
    visual: Canvas,
    /// Actions to be performed when touched
    action: Fn(???) -> T
}

impl InteractiveObject<T> for SimpleTappableObject {
    fn try_activate(&self, swipe: Swipe) -> bool {
        // - check that the swipe is a tap
        // - check that the tap hits the bmap right
    }

    fn action(???) -> T {
       // do that actions
    }

    fn render(&self, canvas: &mut Canvas) {
        // draw on the canvas
    }
}

struct ComplexTappableObject<T> {
    origin: (usize, usize),
    simple_objects: Vec<SimpleTappableObject>,
}

impl InteractiveObject<T> for ComplexTappableObject {
    // similar but different action for different parts
    // maybe force the simple objects to have the same origin/bmap?
}

The d-pad would be composed of 4 simple tappable objects, corresponding to each branch of the d-pad.
The d-pad can thus be manipulated as one object with 4 possible actions.

Maybe Layers could bear such object and non-interactive objects (just stuff with a render method), and we would flatten by drawing in some order. Possible issues: overlapping interactive objects, overlapping objects in the same layer (could check that bmaps are disjunct).

[nbrr]

@richardanaya the example is starting to take form. It displays a d-pad that moves the pine image. It lags a bit some time when you spam tap it, I haven't pin pointed where the delay is coming from, looking at the debug log it doesn't seem to be happening at a specific moment.