Performer specification

This is the engineering specification for the Performer abstract type.

Features

• Named plans
• Composition

Overview

Performers are the objects responsible for executing plans.

MVP

Abstract type

Performer is a protocol, if your language has that concept.

Example pseudo-code:

protocol Performer {}

Not directly configurable

Performers do not provide direct configuration methods.

Performers can only be configured by providing them with plans.

Initialize with target

Performers are initialized with a target.

Example pseudo-code:

performer = Performer(target)

Add plan API

Define an API that allows performers to receive plans.

Example pseudo-code:

function addPlan(plan)

Continuous Performing API

Define an optional API that allows performers to indicate when some continuous work has started and when it eventually ends.

The performer may choose not to implement this API.

A continuous performer is responsible for requesting an is-active token and then terminating it once no longer needed. Consider the following examples:

• Generate a token before an animation begins and terminate the token when the animation completes.
• Generate a token when a gesture begins and terminate the token when the gesture completes.

A runtime is active if at least one is-active token exists that has not yet been terminated, otherwise the runtime is inactive.

Example pseudo-code:

protocol ContinuousPerforming {
  function setIsActiveTokenGenerator(tokenGenerator)
}

class IsActiveTokenGenerator {
  function generate() -> IsActiveToken
}

class IsActiveToken {
  function terminate()
}

Proposed features

Manual execution

A performer can choose to implement an update function that will be called many times per second.

Manual execution API: Define an optional API that allows performers to implement an update function.

The performer may choose not to implement this API.

The update function will be called each time the platform will draw a new frame. The performer may use this method to perform time-based calculations. The performer is not expected to perform any rendering during this update event.

The method returns an activity state enumeration. This enumeration has two states: active and at rest.

Example pseudo-code:

enum ActivityState {
  .Active
  .AtRest
}

protocol ManualPerforming {
  function update(millisecondsSinceLastUpdate) -> ActivityState
}