Events

There are two types of events in Messenger: World Event and User Event. World event is the event Messenger can access while user event is the event users actually receive and it is a subset of the world event as some world event will not send to user.

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

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.