Javascript/jquery速度程序代码不会增加

Question

我不能为我的生活找出为什么我的ball.x在每次调用动画函数时都不会增加0.2？我做了一个工作正常，只是自动增加，但我希望这个增加，当你按左或右。有任何想法吗？？

<script> 
var canvas; 
var context; 
var canvasWidth; 
var canvasHeight; 
var ball = new Ball(); 
ball.radius = 15; 
var vx = 0; 
var ax = 0; 
var keyPressed; 

$(document).ready(function() { 
    canvas = $("#myCanvas"); 
    context = canvas.get(0).getContext("2d"); 
    canvasWidth = canvas.width(); 
    canvasHeight = canvas.height();  
    animate(); 
}); 

function checkKeys(e) { 
    keyPressed = e.keyCode; 
    console.log(keyPressed);  
    if(keyPressed == 37) 
    { 
     ax = -0.2; 
    } 
    if(keyPressed == 39) 
    { 
     ax = 0.2; 
    }  
} 



function animate() { 
    window.requestAnimationFrame(animate, canvas); 
    draw(); 
    //console.log(vx); 
}; 



function draw() { 
    context.clearRect(0,0,canvasWidth, canvasHeight); 
    ball.y = canvasHeight/2; 
    ball.x = canvasWidth/2; 
    vx = vx + ax; 
    ball.x = ball.x + vx; 
    console.log(ball.x);  
    ball.draw(context);        
} 


    </script> 
</head> 

Answer 1

看来你是不是叫checkKeys() - 你在哪里希望这个从叫？