一、canvas图片加载
关于canvas加载，我的方法是，将文章中所有用到图片的地方，都用canvas代替，给canvas一个data-src，里面存放img的路径，通过canvas方法渲染图片。因为图片渲染需要时间，一般会给canvas一个背景，背景可以用gif图片。图片渲染好了之后把背景去掉。
我的canvas代码如下：
canvasload: function () {
//canvas加载图片
var imglength = $("#您的id").find("canvas").length;
if (imglength > ) {
$("#您的id").find("canvas").each(function () {
var imgSrc = $(this).data("src");
var imageObj = new Image();
imageObj.canvs = $(this)[];
var cvs = imageObj.canvs.getContext('2d');
if (cvs) {
imageObj.onload = function () {
imageObj.canvs.width = this.width;
imageObj.canvs.height = this.height;
cvs.drawImage(this, , );
$(imageObj.canvs).css("background-image", "none");
}
imageObj.src = imgSrc;
}
})
}
},
用法很简单，直接在页面中引用这个函数就可以了，注意，所有canvas外层要包裹一个ID
二、图片延迟加载
图片延迟加载方法有很多，下面简单介绍一个，可以引入一个jquery插件。这个插件是一个网友写的，试了一下能用，代码如下：
(function ($) {
$.fn.lazyloading = function (options) {
var defaults = {
preyimg: "/load.gif",
picpath: "data-original",
container: $(window),
loadfirst: false, //进入页面后是否加载当前页面的图片
defaultHeightID: "lazyloadingHeight"//页面上默认高度的input标签id
//imgPaddingID: "lazyloadingPadding"//img的padding值
};
var params = $.extend({}, defaults, options || {});
params.cache = [];
$(this).each(function () {
var node = this.nodeName.toLowerCase(), url = $(this).attr(params["picpath"]), preyimg = params["preyimg"];
var defaultheight = $("#" + params["defaultHeightID"]).val(); //, padding = $("#" + params["imgPaddingID"]).val(); //
//重组
var data = {
obj: $(this),
tag: node,
url: url,
preyimg: preyimg,
defaultheight: defaultheight
};
params.cache.push(data);
});
var init = function () {
$.each(params.cache, function (i, data) {
var thisImg = data.obj, tag = data.tag, url = data.url, preyimg = data.preyimg;
if (typeof (url) != "undefined")// 判断是否需要延迟加载
{
var parent1 = thisImg.parent(); //a
var Inner = null; //
if (parent1.is("a") == true) {//img wrap by a
Inner = parent1;
}
else {
Inner = thisImg;
}
var width = thisImg.attr("width") || thisImg.css("width");
var height = data.defaultheight || thisImg.css("height");
//if (i == 0) alert(data.defaultheight);
var attrheight = thisImg.attr("height");
if (attrheight != null) height = attrheight;
if (width != null && width.indexOf("px") > -) width.replace("px", "");
if (height != null && height.indexOf("px") > -) height.replace("px", "");
var divstr = "<div class='.loading' style='text-align: left;position:relative;float:left;width:" + width + "px;";
var HasHeight = true; //图片是否指定了高度
divstr = divstr + "height:" + height + "px;";
if (attrheight == null || attrheight == "") {
HasHeight = false;
}
thisImg.css("position", "relative");
divstr = divstr + "' ></div>"
//修正外层div：text-align的影响
Inner.wrap(divstr);
//修正img外面不是a标签时parent()已经改变的问题
parent1 = thisImg.parent();
if (HasHeight == true) { parent1.attr("lazyloading_hasheight", ""); } //是否指定了高度
else { { parent1.attr("lazyloading_hasheight", ""); } }
parent1.append("<img class='loadhiddenimg' width='0' height='0' style='display:none;' src='' />");
thisImg.attr("src", preyimg);
thisImg.removeAttr("width").removeAttr("height");
thisImg.attr("width1", width).attr("height1", attrheight);
////thisImg.attr("width", "50px").attr("height", "50px"); //loading图大小
//thisImg.css("margin", "0 auto");
thisImg.css("margin", ((height / ) - ) + "px auto auto " + ((width / ) - ) + "px");
$(".lazyloading").css("display", "table"); //.css("position", "relative");
}
});
}
//动态显示数据
var loading1 = function () { };
var loading = function () {
//窗口的高度+看不见的顶部的高度=屏幕低部距离最顶部的高度
var thisButtomTop = parseInt($(window).height()) + parseInt($(window).scrollTop());
var thisTop = parseInt($(window).scrollTop()); //屏幕顶部距离最顶部的高度
$.each(params.cache, function (i, data) {
var thisImg = data.obj, tag = data.tag, url = data.url, post, posb;
if (thisImg) {//对象不为空
if (typeof (url) != "undefined") {// 判断是否需要延迟加载
var PictureTop = parseInt(thisImg.offset().top);
//如果处理可见范围内，并且原图地址data-original不等于src,则加载图片
if (PictureTop >= thisTop && PictureTop <= thisButtomTop && thisImg.attr("data-original") != thisImg.attr("src")) {
var hiddenImg = thisImg.siblings("img.loadhiddenimg");
hiddenImg.load(function () { //隐藏图片加载完之后的回调函数
var width = thisImg.attr("width1");
var height = thisImg.attr("height1");
thisImg.attr("width", width).attr("height", height).removeAttr("width1").removeAttr("height1");
thisImg.css("margin", "0 auto");
if (thisImg.parent().attr("lazyloading_hasheight") == "") {//没有指定高度时，加载图片后去掉div高度自适应
if (thisImg.parent().is("a") == true) {
thisImg.parent().parent().css("height", "");
}
else {
thisImg.parent().css("height", "");
}
}
thisImg.load(function () {
if (thisImg.parent().is("a") == true) {
thisImg.parent().parent().css("height", thisImg.height());
}
else {
thisImg.parent().css("height", thisImg.height());
}
});
thisImg.css('opacity', '0.2');
thisImg.attr("src", hiddenImg.attr("src"));
thisImg.animate({ opacity: 1.0 });
if (thisImg.attr("alt") != "") {
thisImg.attr("title", thisImg.attr("alt"));
thisImg.attr("alt", "");
}
}).error(function () {
thisImg.error(function () {
thisImg.css("margin", "0 auto auto 0");
if (thisImg.parent().attr("lazyloading_hasheight") == "") {//没有指定高度时，加载图片后去掉div高度自适应
if (thisImg.parent().is("a") == true) {
thisImg.parent().parent().css("height", "");
}
else {
thisImg.parent().css("height", "");
}
}
});
thisImg.attr("src", hiddenImg.attr("src")); //alert("error");
if (thisImg.attr("alt") != "") {
thisImg.attr("title", thisImg.attr("alt"));
thisImg.attr("alt", "");
}
});
hiddenImg.attr("src", url);
}
}
}
});
};
//初始化
init();
//事件触发
//加载完毕即执行
if (params["loadfirst"] == true) loading();
//滚动执行
params.container.bind("scroll", loading).bind("resize", loading);
};
})(jQuery);
用法很简单：
<a href="#"><img alt="haorooms博客" src="" data-original="http://www.haorooms.com/uploads/images/table.gif" class="lazyloading" /></a>
<script type="text/javascript">
$(function () {
$("img.lazyloading").lazyloading({ loadfirst: true });
}) </script>
