core2d/src/plugin/Starfield.mjs

Multiplatform 2D interaction engine

"use strict";

import { Color } from "../Color.mjs";
import { Core2D } from "../Core2D.mjs";
import { Sprite } from "../Sprite.mjs";

const SPEED_SIZE_RATIO = 0.25;
const STAR_BLINK_CHANCE = 10;
const STAR_DENSITY = 100;

class Star extends Sprite {
  init() {
    this.addTag("star").setBoundary();
  }

  offBoundary() {
    if (this.right < this.scene.left) {
      this.setLeft(this.scene.right);
    } else if (this.left > this.scene.right) {
      this.setRight(this.scene.left);
    }

    if (this.bottom < this.scene.top) {
      this.setTop(this.scene.bottom);
    } else if (this.top > this.scene.bottom) {
      this.setBottom(this.scene.top);
    }
  }

  update() {
    this.setVisible(Core2D.random(STAR_BLINK_CHANCE * this.width) > 0);
  }
}

export class Starfield extends Sprite {
  constructor() {
    super();
    this.colors = [Color.White];
  }

  init() {
    for (let i = 0; i < STAR_DENSITY; ++i) {
      const SIZE = 1 + Core2D.random(1);

      this.scene.add(
        new Star()
          .setColor(this.colors[Core2D.random(this.colors.length - 1)])
          .setX(Core2D.random(this.scene.width))
          .setY(Core2D.random(this.scene.height))
          .setWidth(SIZE)
          .setHeight(SIZE)
          .setSpeedX(this.speedX * SIZE * SPEED_SIZE_RATIO)
          .setSpeedY(this.speedY * SIZE * SPEED_SIZE_RATIO)
      );
    }
  }

  setColors(colors) {
    this.colors = colors;
    return this;
  }
}