enemies.js

class Enemy{
    constructor(){
        this.frameX=0
        this.frameY=0
        this.fps=20
        this.frameInterval=1000/this.fps
        this.frameTimer=0
        this.markedForDeletion=false
    }
    update(deltaTime){
        this.x-=this.speedX+this.game.speed
        this.y+=this.speedY
        if(this.frameTimer>this.frameInterval){
            this.frameTimer=0
            if(this.frameX<this.maxFrame) this.frameX++
            else this.frameX=0
        }else{
            this.frameTimer+=deltaTime
        }
        // 对敌人进行检查，超过屏幕就进行删除
        if(this.x+this.width<0) this.markedForDeletion=true
    }
    draw(context){
        if(this.game.debug){
            context.strokeRect(this.x,this.y,this.width,this.height)
        }
        context.drawImage(this.image,this.frameX*this.width,0,this.width,this.height,this.x,this.y,this.width,this.height)
    }
}
export class FlyingEnemy extends Enemy{
    constructor(game){
        super()
        this.game=game
        this.width=60
        this.height=44
        this.x=this.game.width
        this.y=Math.random()*this.game.height*0.5
        this.speedX=Math.random()+1
        this.speedY=0
        this.maxFrame=5
        this.image=document.getElementById('enemy_fly')
        this.angle=0
        this.va=Math.random()*0.1+0.1
    }
    update(deltaTime){
        super.update(deltaTime)
        this.angle+=this.va
        this.y+=Math.sin(this.angle)
    }
}
export class GroundEnemy extends Enemy{
    constructor(game){
        super()
        this.game=game
        this.width=60
        this.height=87
        this.x=this.game.width
        this.y=this.game.height-this.height-this.game.groundMargin
        this.speedX=0
        this.speedY=0
        this.maxFrame=1
        this.image=document.getElementById('enemy_plant')
    }
}
export class ClimbingEnemy extends Enemy{
    constructor(game){
        super()
        this.game=game
        this.width=120
        this.height=144
        this.x=this.game.width
        this.y=Math.random()*this.game.height*0.5
        this.image=document.getElementById('enemy_spider_big')
        this.speedX=0
        this.speedY=Math.random()>0.5?1:-1
        this.maxFrame=5
    }
    update(deltaTime){
        super.update(deltaTime)
        if(this.y>this.game.height-this.height-this.game.groundMargin) this.speedY*=-1
        if(this.y<-this.height) this.markedForDeletion=true
    }
    draw(context){
        super.draw(context)
        context.beginPath()
        context.moveTo(this.x+this.width/2,0)
        context.lineTo(this.x+this.width/2,this.y)
        context.stroke()
    }
}