Coroutines

A coroutine allows you to spread tasks across several frames.

Example: Random Movement With Delay

import { Component, CoroutineIterator, WaitForSeconds } from "the-world-engine";

export class RandomMovement extends Component {
    private readonly _range = 6;
    
    public awake(): void {
        this.startCoroutine(this.move());
    }

    private *move(): CoroutineIterator {
        for (; ;) {
            const x = Math.random() * this._range - this._range / 2;
            const y = Math.random() * this._range - this._range / 2;
            this.gameObject.transform.position.set(x, y, 0); //move to random position

            yield new WaitForSeconds(1); //wait for 1 second
        }
    }
}

Example: Waiting Promise

Async/await is not available in the component, but you can wait for Promise using Coroutine

export class ImageSpawner extends Component {
    public spawn(query: string): void {
        this.startCoroutine(this.spawnInternal(query));
    }

    private *spawnInternal(query: string): CoroutineIterator {
        let imageSearchResults: SearchResult[]|null = null;
        ImageSearch.fatch(query).then(images => imageSearchResults = images);
        yield new WaitWhile(() => imageSearchResults === null);

        for (const image of imageSearchResults!) {
            //spawn image
        }
    }
}

Yield Instructions

The control flow can be handed over to the engine using the yield instruction.

• yield null: Wait for next frame
• yield new WaitForSeconds(1): Wait for 1 second
• yield new WaitForEndOfFrame: Wait for end of frame
• yield new WaitUntil(() => false): Wait until condition is false
• yield new WaitWhile(() => true): Wait while condition is true