画布性能下降几秒钟后 [英] canvas performance drop after a few seconds

问题描述

我写了以下1000个边界正方形演示作为HTML5画布的功能测试。它首先运行良好，但在几秒钟后，一个明显的f​​ps下降。我不知道为什么。任何指针都会感激。

I wrote the following 1000 bounding squares demo as a test of the capabilities of HTML5 canvas. It runs fine at first but then a noticeable drop in fps after a few seconds. I am not sure why. Any pointers would be appreciated.

var c = document.getElementById("canvas");
var context = c.getContext("2d");

var WIDTH = 600;
var HEIGHT = 800;

c.width = WIDTH;
c.height = HEIGHT;

image = loadImage("square.png");

function loadImage(imageName){
    var i = new Image();
    i.src = imageName;
    return i;
}


function clear(){
    context.fillStyle = "#d0e7f9";
    context.rect(0,0,WIDTH,HEIGHT);
    context.fill();
}
clear();

var SpriteList = [];

var Sprite = (function() { //javascript class(?)... shredders
    function Sprite(){  //constructor
        this.x = Math.random()*WIDTH;
        this.y = Math.random()*HEIGHT;
        this.vx = Math.random()*10;
        this.vy = Math.random()*10;
        SpriteList.push(this);
    }

    Sprite.prototype.update = function(){
        this.x += this.vx;
        this.y += this.vy;

        if (this.x<0 || this.x>WIDTH){
            this.vx *= -1;
        }
        if (this.y<0 || this.y>HEIGHT){
            this.vy *= -1;
        }
    };

    return Sprite;
})();

for (var i = 0;i<1000;i++){
    new Sprite();
}

function draw(){
    clear();
    for (i in SpriteList)
    {
        var s = SpriteList[i];
        s.update();
        context.drawImage(image, s.x, s.y);
    }
}

setInterval(draw,1000/60);

推荐答案

代码有几个问题，原因是这个代码：

There are a few issues with the code but the main reason for this to happen is this code:

这段代码需要你使用 beginPath（）：

This code will require you to use beginPath():

function clear(){
    context.fillStyle = "#d0e7f9";
    context.beginPath();
    context.rect(0,0,WIDTH,HEIGHT); /// this will require beginPath();
    context.fill();
}

或者为了避免它，你可以简单地修改代码： / p>

or to avoid it, you can simply modify the code to do this:

function clear(){
    context.fillStyle = "#d0e7f9";
    context.fillRect(0,0,WIDTH,HEIGHT); /// this does not require beginPath();
}

Live fiddle here

Live fiddle here

/// use a var here    
var image = loadImage("square.png");

/// your image loader is missing - image may not show up
function loadImage(imageName){
    var i = new Image();
    i.onload = nextStep; /// something like this
    i.src = imageName;
    return i;
}

var SpriteList = [];

/// create this as an object
function Sprite(){  //constructor
    this.x = Math.random()*WIDTH;
    this.y = Math.random()*HEIGHT;
    this.vx = Math.random()*10;
    this.vy = Math.random()*10;
    return this;
}

Sprite.prototype.update = function(){
    this.x += this.vx;
    this.y += this.vy;

    if (this.x<0 || this.x>WIDTH){
        this.vx *= -1;
    }
    if (this.y<0 || this.y>HEIGHT){
        this.vy *= -1;
    }
};

/// separate pushing of the instances
for (var i = 0;i<1000;i++){
    SpriteList.push(new Sprite());
}

var oldTime = 0;

function draw(timeElapsed){ /// in milliseconds
    clear();

    var diffTime = timeElapsed - oldTime;

    /// use vars here too
    for (var i = 0, s; s = SpriteList[i]; i++ )
    {
        s.update();
        context.drawImage(image, s.x, s.y);
    }

    oldTime = timeElapsed;

    /// use rAF here
    requestAnimationFrame(draw);
}

draw(0); /// start

setInterval

通过使用rAF，浏览器只会请求一个框架即使这意味着更低的帧速率 - 您至少不会锁定/减慢浏览器。

By using rAF the browser will only request a frame when it can even if that means lower frame rates - you will at least not lock up/slow down the browser.

（因为您没有提供图像的链接你使用我用一个临时画布替换它 - 你仍然需要考虑一个 onload 事件处理程序的实际图像）。

(as you didn't provide a link to the image you're using I substituted it with a temp canvas - you will still need to consider a onload event handler for the actual image).

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