HTML5/Javascript -尝试将画布动画绑定到键盘事件

HTML5/Javascript - Trying to get bind a canvas animation to a keyboard event

本文关键字：动画 绑定 事件 键盘 布动画 Javascript HTML5      更新时间：2023-09-26

这是我第一次在javascript中做键盘事件，但我知道动画是有效的。这个想法很简单:当用户按下回车键时，播放一个矩形移动的动画。下面是我的代码。

//Event listeners
window.addEventListener("keydown", onKeyDown, false);
function onKeyDown(event){
    var keyCode = event.keyCode;
    switch(keyCode){
        case 13  //enter
            drawStuff();
        break;
    }
}
//code to be executed onKeyDown
function drawStuff(){
var x = document.getElementById("myCanvas");
var canvas = x.getContext('2d');
var i = 0;
function animate(){
    if(i < 451){
        canvas.clearRect(0,0,500,500);
        canvas.fillStyle="red";
        canvas.fillRect(30,i,50,50);
        i++;
    }
    else{}
}
window.setInterval(animate, 1);
}

有什么建议如何解决这个问题?

看看Paul Irish的requestAnimationFrame shim;相对于setInterval方法，rAF有很多优点;主要是因为它是为了这样做而构建的，但它也只在浏览器准备好时请求帧，所以当你的网站在后台时，它会暂停发生的事情。我还注意到当我切换到

时，性能更流畅了。

我想说这样应该可以工作:

var animationHasTriggered = false;
var x = document.getElementById("myCanvas");
var canvas = x.getContext('2d');
var keysDown = {};
var i = 0;
window.addEventListener('load', function()
{
    addEventListener("keydown", function(e)
    {
        keysDown[e.keyCode] = true;
    }, false);
    addEventListener("keyup", function(e)
    {
        delete keysDown[e.keyCode];
    }, false);
    updateAll();
}, false);
function updateAll()
{
    if (13 in keysDown || animationHasTriggered)
    {
        animationHasTriggered = true;
        animate();
    }
    requestAnimationFrame(updateAll);
}
function animate()
{
    if (i < 451)
    {
        canvas.clearRect(0,0,500,500);
        canvas.fillStyle="red";
        canvas.fillRect(30,i,50,50);
        i++;
    }
    else
    {
        animationHasTriggered = false;
    }
}
(function()
{
    // http://paulirish.com/2011/requestanimationframe-for-smart-animating/
    var lastTime = 0;
    var vendors = ['ms', 'moz', 'webkit', 'o'];
    for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x)
    {
        window.requestAnimationFrame = window[vendors[x]+'RequestAnimationFrame'];
        window.cancelAnimationFrame = window[vendors[x]+'CancelAnimationFrame'] || window[vendors[x]+'CancelRequestAnimationFrame'];
    }
    if (!window.requestAnimationFrame) window.requestAnimationFrame = function(callback, element)
    {
        var currTime = new Date().getTime();
        var timeToCall = Math.max(0, 16 - (currTime - lastTime));
        var id = window.setTimeout(function()
        {
            callback(currTime + timeToCall);
        }, timeToCall);
        lastTime = currTime + timeToCall;
        return id;
    };
    if (!window.cancelAnimationFrame) window.cancelAnimationFrame = function(id)
    {
        clearTimeout(id);
    };
}());
相关文章：