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/******************************************************
* jQuery plug-in
* Easy Background Image Resizer
* Developed by J.P. Given (http://johnpatrickgiven.com)
* Useage: anyone so long as credit is left alone
******************************************************/
(function($) {
// Global Namespace
var jqez = {};
// Define the plugin
$.fn.ezBgResize = function(options) {
// Set global to obj passed
jqez = options;
// If img option is string convert to array.
// This is in preparation for accepting an slideshow of images.
if (!$.isArray(jqez.img)) {
var tmp_img = jqez.img;
jqez.img = [tmp_img]
}
$("<img/>").attr("src", jqez.img).load(function() {
jqez.width = this.width;
jqez.height = this.height;
// Create a unique div container
$("body").append('<div id="jq_ez_bg"></div>');
// Add the image to it.
$("#jq_ez_bg").html('<img src="' + jqez.img[0] + '" width="' + jqez.width + '" height="' + jqez.height + '" border="0">');
// First position object
$("#jq_ez_bg").css("visibility","hidden");
// Overflow set to hidden so scroll bars don't mess up image size.
$("body").css({
"overflow":"hidden"
});
resizeImage();
});
};
$(window).bind("resize", function() {
resizeImage();
});
// Actual resize function
function resizeImage() {
$("#jq_ez_bg").css({
"position":"fixed",
"top":"0px",
"left":"0px",
"z-index":"-1",
"overflow":"hidden",
"width":$(window).width() + "px",
"height":$(window).height() + "px",
"opacity" : jqez.opacity
});
// Image relative to its container
$("#jq_ez_bg").children("img").css("position", "relative");
//Resize the img object to the proper ratio of the window
var iw = $("#jq_ez_bg").children("img").width();
var ih = $("#jq_ez_bg").children("img").height();
if ($(window).width() > $(window).height()) {
console.log(iw, ih);
if (iw > ih) {
//一是这里无法理解这个 是算比例吗???
var fRatio = iw/ih;
$("#jq_ez_bg").children("img").css("width",$(window).width() + "px");
//还有这里的 Math.round($(window).height() * (1/fRatio)) 前面为什么要用窗口的高度,和 后面的为什么要用 1来除,,这又是为了什么???
$("#jq_ez_bg").children("img").css("height",Math.round($(window).width() * (1/fRatio)));
var newIh = Math.round($(window).width() * (1/fRatio));
if(newIh < $(window).height()) {
var fRatio = ih/iw;
$("#jq_ez_bg").children("img").css("height",$(window).height());
$("#jq_ez_bg").children("img").css("width",Math.round($(window).height() * (1/fRatio)));
}
} else {
var fRatio = ih/iw;
$("#jq_ez_bg").children("img").css("height",$(window).height());
$("#jq_ez_bg").children("img").css("width",Math.round($(window).height() * (1/fRatio)));
}
} else {
var fRatio = ih/iw;
$("#jq_ez_bg").children("img").css("height",$(window).height());
$("#jq_ez_bg").children("img").css("width",Math.round($(window).height() * (1/fRatio)));
}
// Center the image
if (typeof(jqez.center) == "undefined" || jqez.center) {
if ($("#jq_ez_bg").children("img").width() > $(window).width()) {
var this_left = ($("#jq_ez_bg").children("img").width() - $(window).width()) / 2;
$("#jq_ez_bg").children("img").css({
"top" : 0,
"left" : -this_left
});
}
if ($("#jq_ez_bg").children("img").height() > $(window).height()) {
var this_height = ($("#jq_ez_bg").children("img").height() - $(window).height()) / 2;
$("#jq_ez_bg").children("img").css({
"left" : 0,
"top" : -this_height
});
}
}
$("#jq_ez_bg").css({
"visibility" : "visible"
});
// Allow scrolling again
$("body").css({
"overflow":"auto"
});
}
})(jQuery);
<body style="position:relative;z-index:0;">
<img style="position:fixed;top:0;left:0;width:100%;height:100%;z-index:0;" data-src="1.jpeg" />
<!-- HTML5 延迟加载,不影响页面整体加载速度 -->
<div id="wrap" style="position:relative;z-index:1;background:transparent;">
<!-- 网页内容 -->
</div>
</body>