请问这个动画效果怎么实现

var app = new PIXI.Application(600,500);
document.body.appendChild(app.view);

var bg = new PIXI.Sprite.fromImage("res/pao/ground01_2.png");
app.stage.addChild(bg);
bg.y = 300;

var ball = new PIXI.Sprite.fromImage("res/lianxi/llball/ball.png");
app.stage.addChild(ball);
ball.y = 240;

function animate() {
    ball.x+=1;
    if(ball.x>=280 && ball.x<=440){
        ball.y+=;
    }
    
}
app.ticker.add(animate);

function animate() {
    ball.x+=1;
    if(ball.x>=280 && ball.x<=440){
        ball.y+=1;
    }
    
}

有用望采纳