roundabout/src/pages/game/algorithm/bullet.js

import Two from "two.js";
import { scale, desginCageRadius, pedestalOffsetX, pedestalOffsetY, cageNum } from './design'
import bulletImage from '@/assets/RoundaboutImage/2-13.png';

// 子弹的核心逻辑
export default ({two, center, speed, getGameState}) => {
  const _event = new Two.Events()

  // 子弹个数 = 轿厢个数
  const num = cageNum;
  // 子弹宽度 = 轿厢宽度
  const bulletRadius = desginCageRadius;

  // 子弹其实位置与底座是一致的
  const x = center.x + pedestalOffsetX * scale;
  const y = center.y + pedestalOffsetY * scale;

  // 弹夹
  let clip = [];
  // 在膛子弹
  let current = null;
  
  // 绘制子弹
  function drawBullets () {
    const bulletTexture = two.makeTexture(bulletImage);
  
    const list = Array(num).fill().map((_, inx) => {
      const arc = two.makeCircle(x, y, bulletRadius)
      arc.id = `bullet-${inx}`
      // arc.fill = 'black'
      arc.fill = bulletTexture
      arc.noStroke()
      arc.scale = scale;
      arc.visible = false; // 默认不显示, 即不上膛
  
      return arc
    })

    return list;
  }

  // 子弹上膛
  function bulletLoad() {
    current = clip.shift()
    if (current) {
      current.visible = true
    }
  }
  
  // 子弹飞行
  function fly() {
    if (!current) return;
    const { top, height } = current.getBoundingClientRect()
    current.position = new Two.Vector(current.position.x, current.position.y + speed)

    // 子弹飞行事件
    _event.dispatchEvent('shooting', { 
      bullet: current,
      cancel: () => {
        two.removeEventListener('update', fly);
        _event.dispatchEvent('afterShoot');
      },
     })
  }

  // 射击
  function shoot() {
    if (getGameState() !== 1) return;

    _event.dispatchEvent('beforeShoot')
    two.addEventListener('update', fly)
  }

  // 弹夹
  clip = drawBullets()
  
  return {
    on: _event.on.bind(_event),
    bulletLoad,
    shoot,
  }
}