[英]how to pause a html5 canvas javascript animation with a keyboard input
[英]HTML5/Javascript - Trying to get bind a canvas animation to a keyboard event
这是我第一次使用JavaScript进行键盘事件,但事实上我知道动画是有效的。 这个想法很简单:播放用户按下Enter键时移动的矩形动画。 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);
}
任何建议如何解决此问题?
看看Paul Irish的requestAnimationFrame
垫片 ; 与setInterval方法相比,rAF具有许多优点; 主要是因为它是专门为执行此操作而构建的,而且它仅在浏览器就绪时才请求帧,因此它可以暂停您的网站在后台运行时发生的事情。 切换时,我还注意到性能更流畅。
我说这样的事情应该起作用:
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);
};
}());
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