游戏的趣味性在与各种关卡和难度,游戏的难度如上台阶,具有层层递进的性质。本节我们为太空防御游戏增加关卡功能,让游戏的难度由低到高,每一关我们称作一个冲击波,前面的冲击波,外星人的数量比较少,下落速度也相对较慢,等到后面的冲击波时,外星人的数量会越来越多,速度和攻击力越来越大,于是游戏的难度也逐渐变大。

当完成本节代码后,我们会得到如下效果,在每一轮冲击波开始时,界面会出现如下信号:
这里写图片描述

当游戏进行到后几轮冲击波时,外星人数量和种类越来越多,战况越来越激烈:

这里写图片描述

我们看看代码的实现,在gamescenecomponent.vue中添加新的数据结构:

export default {
    data () {
      return {
      ....
      // change 1
        waves: {}
      }
    },
    methods: {
      init () {
      ....
      // change 2
      this.initWaves()
      this.startWave()
      ...
      },
      // change 3
      initWaves () {
        console.log('begin init wave')
        this.waves.nextWave = 0
        this.waves.isActive = false
        // 定义一轮冲击波中外星人从天而降的次序
        this.waves.enemySummonOrder = ['EnemyDummy', 'Enemy1', 'Enemy2', 'Enemy3', 'Boss', 'Boss2']
        console.log('init wave data')
        this.waves.data = [
        // 第一轮冲击波
        {'EnemyDummy': 1, frequency: 10},
        // 第二轮冲击波
        {'EnemyDummy': 8, 'Enemy1': 5, 'Enemy2': 5, 'Boss': 2, frequency: 150},
        // 第三轮冲击波
        {'EnemyDummy': 1, 'Enemy1': 1, 'Enemy2': 1, 'Enemy3': 1, 'Boss': 1, 'Boss2': 30, frequency: 50}
        ]
        console.log('init wave sprite')
        this.nextWaveSprite = new this.assetsLib.WaveCleared()
        this.stage.addChild(this.nextWaveSprite)
        this.nextWaveSprite.x = 999
      },

      // change4 启动一轮外星人攻击的冲击波
      startWave () {
        this.energies = 120
        this.waves.currentWave = this.waves.data[this.waves.nextWave]
        this.waves.isActive = true
        this.waves.enemiesSummoned = 0
      },

      // change 5
      wavesCleared () {
        this.waves.nextWave += 1
        if (this.waves.nextWave >= this.waves.data.length) {
          this.waves.nextWave = this.waves.data.length - 1
        }
      },
}

上面代码定义了外星人攻击冲击波的数据结构,其中定义了每一轮攻击过程中,外星人的种类和数量,在每一轮冲击波启动前,页面会出现“wave cleared”的字体显示特效,startWave启动新一轮冲击波流程,wavesCleared在冲击波结束后,负责清理页面和各种数据结构。接下来我们实现冲击波流程的动态效果:

// change 6
      waveTick () {
        if (!this.waves.isActive) {
          return
        }

        if (this.cjs.Ticker.getTicks() % this.waves.currentWave.frequency === 0) {
          // 依次把不同种类的外星人召唤出来
          var accumunateTargetCount = 0
          for (var i = 0, len = this.waves.enemySummonOrder.length; i < len; i++) {
            var enemyType = this.waves.enemySummonOrder[i]
            // 获得外星人个数
            var targetCount = this.waves.currentWave[enemyType] || 0
            accumunateTargetCount += targetCount
            if (this.waves.enemiesSummoned < accumunateTargetCount) {
              break
            }
          }

          if (this.waves.enemiesSummoned >= accumunateTargetCount) {
            this.waves.isActive = false
          } else {
            this.addEnemy(enemyType)
            this.waves.enemiesSummoned += 1
          }
        }
      },
      tick () {
      ....
       // change 9
        this.wavesSpan.textContent = this.waves.nextWave + 1

        this.boardTick()

        // change 7
        this.waveTick()
        if (!this.waves.isActive && this.areEnemiesCleared()) {
          this.boardLayer.isAddingBuilding = false
          this.removeAllBuildings()
          this.removeAllBullets()
          this.wavesCleared()

          // 显示字体动画
          this.cjs.Tween.get(this.nextWaveSprite).to({x: this.canvas.width / 2, y: this.canvas.height / 2, alpha: 0}).to({alpha: 1.0}, 300).wait(1000).to({alpha: 0}, 300).to({x: 999})

          this.startWave()
        }
      },
      // change 8
      removeAllBuildings () {
        for (var i = 0; i < this.boardLayer.cols; i++) {
          for (var j = 0; j < this.boardLayer.rows; j++) {
            this.removeBuilding(this.boardLayer.buildingMap[i][j])
          }
        }

        this.satelliteList = []
        this.castleList = []
      },
      areEnemiesCleared () {
        return this.enemyList.length === 0
      },
      removeAllBullets () {
        this.bulletList.length = 0
        this.effectLayer.removeAllChildren()
      },

waveTick函数用于在冲击波进行的过程中不断的更新页面。每一轮冲击波有哪些种类的外星人已经外星人数量是多少,都是由wave.data中定义的数据决定的。waveTick的作用是把wave.data中定义的外星人种类和数量加载到页面上,然后刷新页面,实现页面动态效果。waveTick是在时钟函数tick中被调用的,在tick函数中,一旦判断到一轮冲击波结束时,他们把”wave cleared”的字体特效显示到页面上,就如开头图片展示的那样。removeAllBuildings和removeAllBullets负责在一轮冲击波结束时,将页面上的建筑物和飞翔的子弹清除掉。最后我们从资源库中将不停种类的外星人资源加载到浏览器里,并在合适的时候将他们描绘在页面上:

// change 9
      enemy1 () {
        console.log('enemy1')
        var enemy1 = this.enemy()
        enemy1.addChild(new this.assetsLib.Enemy1())
        enemy1.attackSpeed = 50
        enemy1.speed = enemy1.originalSpeed
        enemy1.name = 'enemy1'

        return enemy1
      },
      enemy2 () {
        console.log('enemy2')
        var enemy2 = this.enemy()
        enemy2.addChild(new this.assetsLib.Enemy2())
        enemy2.originalSpeed = 1.0
        enemy2.attackSpeed = 40
        enemy2.hp = 8
        enemy2.deceleration = 0.008
        enemy2.speed = enemy2.originalSpeed
        enemy2.name = 'enemy2'

        return enemy2
      },
      boss2 () {
        var bossEnemy = this.enemy()
        bossEnemy.addChild(new this.assetsLib.Boss2())
        bossEnemy.originalSpeed = 0.2
        bossEnemy.deceleration = 0.002
        bossEnemy.hp = 300
        bossEnemy.attackSpeed = 50

        bossEnemy.name = 'boss'
        return bossEnemy
      },
      enemy3 () {
        console.log('enemy3')
        var enemy3 = this.enemy()
        enemy3.addChild(new this.assetsLib.Enemy3())
        enemy3.originalSpeed = 3.0
        enemy3.attackSpeed = 10
        enemy3.hp = 8
        enemy3.deceleration = 0.002
        enemy3.speed = enemy3.originalSpeed
        enemy3.name = 'enemy3'

        return enemy3
      },

完成上面代码后,我们就可以看到如开头第二幅图那样的,五花八门的外星人从天而降,我们在底部架起各种炮台和建筑打击外星人,整幅画面具有星球大战般的绚丽感。

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这里写图片描述

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