Events

Messenger internally uses world events from browser subscriptions and ports, but user code works with User Event. WorldEvent is an internal runtime type and is not part of normal user code.

type UserEvent
    = Tick Float
    | KeyDown Int
    | KeyUp Int
    | MouseDown Int ( Float, Float )
    | MouseUp Int ( Float, Float )
    | MouseWheel Int
    | Prompt String String

Every general model (layer, component) will use UserEvent when updating. Recall the update function:

update : envro -> env -> event -> data -> bdata -> ( ( data, bdata ), List (Msg tar msg sommsg), ( env, Bool ) )

The envro argument is read-only runtime context; in Messenger-specific models it is Runtime. The last Bool is a block indicator. Every general model is able to block event from sending to the next general components when updating.

note

The order of updating layers in a scene is opposite to the order of rendering layers in a scene. This mechanism is designed to enable layers to block messages from passing to the layers behind it. This is useful when you are handling mouse events. When a layer handles a mouse click event, you don't want other layers to also be triggered.

Take an example, there are two layers in the scene in the order of [A, B] when initializing the scene. This means that A is rendered before B but A will be updated after B. Suppose the update of A emits [A1, A2] SOMMsgs and B emits [B1, B2] SOMMsgs, then the core will handle SOMMsg in the order of B1, B2, A1, A2.