BurstSpawn.ts

import { Particle } from '../Particle';
import { IEmitterBehavior, BehaviorOrder } from './Behaviors';
import { DEG_TO_RADS, rotatePoint } from '../ParticleUtils';
import { BehaviorEditorConfig } from './editor/Types';

/**
 * A Spawn behavior that sends particles out from a single point or ring, and is capable of evenly spacing
 * the particle's starting angles.
 *
 * Example config:
 * ```javascript
 * {
 *     type: 'spawnBurst',
 *     config: {
 *          spacing: 90,
 *          start: 0,
 *          distance: 40,
 *     }
 * }
 * ```
 */
export class BurstSpawnBehavior implements IEmitterBehavior
{
    public static type = 'spawnBurst';
    public static editorConfig: BehaviorEditorConfig = null;

    order = BehaviorOrder.Spawn;
    private spacing: number;
    private start: number;
    private distance: number;

    constructor(config: {
        /**
         * Description: Spacing between each particle spawned in a wave, in degrees.
         */
        spacing: number;
        /**
         * Description: Angle to start placing particles at, in degrees. 0 is facing right, 90 is facing upwards.
         */
        start: number;
        /**
         * Description: Distance from the emitter to spawn particles, forming a ring/arc.
         */
        distance: number;
    })
    {
        this.spacing = config.spacing * DEG_TO_RADS;
        this.start = config.start * DEG_TO_RADS;
        this.distance = config.distance;
    }

    initParticles(first: Particle): void
    {
        let count = 0;
        let next = first;

        while (next)
        {
            let angle: number;

            if (this.spacing)
            {
                angle = this.start + (this.spacing * count);
            }
            else
            {
                angle = Math.random() * Math.PI * 2;
            }

            next.rotation = angle;
            if (this.distance)
            {
                next.position.x = this.distance;
                rotatePoint(angle, next.position);
            }
            next = next.next;
            ++count;
        }
    }
}