Gesso.Application.Behavior

type FixedUpdate state = { function :: UpdateFunction state, interval :: Interval }

An update function that occurs at a fixed, regular interval, rather than on every animation frame.

type InputReceiver state input = input -> UpdateFunction state

An input receiver is a variant of an update function that can receive information from the component's parent and produce an update function in response.

type OutputProducer state output = Delta -> Scalers -> Compare state -> Effect (Maybe output)

When the state of an application changes, an output producer compares the old and new states and may send output to the component's parent based on the difference.

type RenderFunction state = Context2D -> Delta -> Scalers -> States state -> Effect Unit

A function that draws on the component. It knows the following:

• Context2D is the drawing context of the canvas element
• Delta is a record containing current and previous timestamps and the time elapsed since the previous frame.
• Scalers is a record containing scaling information for transforming coordinates between the drawing and the canvas.
• state is the state of the application, with States containing the two most recent states and the time progress between them (on the interval [0, 1]).

The render function may run any operations in Effect, not just functions related to drawing on the canvas.

type TimestampedUpdate state = Scalers -> state -> Effect (Maybe state)

A partially applied UpdateFunction that already has the Delta record.

type UpdateFunction state = Delta -> TimestampedUpdate state

An function that may update the application state. It runs on every frame, before the render function. It knows the following:

• Delta is a record containing current and previous timestamps and the time elapsed since the previous frame.
• Scalers is a record containing scaling information for transforming coordinates between the drawing and the canvas.
• state is the state of the application

The update function may return a new state if changes are necessary (or Nothing if not).

This type is also used by Interaction handlers and when receiving input from a host application.