如何实现登录框鼠标拖拽效果

<!DOCTYPE html>

<head>

<title>登录框鼠标拖拽效果</title>

body {

background: url("https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1488778794834&di=e97c96dfe7860297d1968c30adc862a2&imgtype=0&src=http%3A%2F%2Fpic1.5442.com%3A82%2F2015%2F0409%2F01%2F15.jpg%2521960.jpg") no-repeat top center #ffffff;

background-size: 100%;

padding: 0;

margin: 0;

font-size: 12px;

font-family: "微软雅黑", sans-serif;

}

.ui-dialog {

width: 380px;

position: absolute;

z-index: 9000;

top: 100px;

left: 100px;

border: 1px solid #d5d5d5;

background-color: #ffffff;

/*display: none;*/

}

.ui-dialog-title {

height: 48px;

line-height: 48px;

padding-left: 20px;

color: #535353;

font-size: 16px;

background-color: #f5f5f5;

border-bottom: 1px solid #efefef;

cursor: move;

}

.ui-dialog-title-closebutton {

width: 16px;

height: 16px;

display: inline-block;

position: absolute;

right: 20px;

color: #000;

text-decoration: unset;

}

.ui-dialog-title-closebutton:hover {

color: #4ca8ff;

}

.ui-dialog-content {

padding: 15px 20px;

}

.ui-dialog-pt15 {

padding-top: 15px;

}

.ui-dialog-l40 {

height: 40px;

line-height: 40px;

text-align: right;

}

.ui-dialog-input {

width: 100%;

height: 40px;

margin: 0;

padding: 0;

border:1px solid #d5d5d5;

font-size: 16px;

color: #c1c1c1;

text-indent: 25px;

outline: none;

}

.ui-dialog-input-username {

background: url("images/input_username.png") no-repeat 2px;

}

.ui-dialog-input-password {

background: url("images/input_password.png") no-repeat 2px;

}

.ui-dialog-submit {

width: 100%;

height: 50px;

background: #3b7ae3;

border: none;

font-size: 16px;

color: #ffffff;

outline: none;

text-decoration: none;

display: block;

text-align: center;

line-height: 50px;

}

.ui-dialog-submit:hover {

background: #3f81b0;

}

.ui-mask {

width: 100%;

height: 100%;

background: #000;

opacity: 0.4;

position: absolute;

top: 0;

left: 0;

z-index: 8000;

display: none;

}

.link {

text-align: right;

line-height: 20px;

padding-right: 40px;

}

</style>

</head>

<body>

</div>

</div>

</div>

</div>

<div>

</div>

</div>

</div>

// 获取元素对象

function g(id) {

return document.getElementById(id);

}

// 自动居中函数 -- 登录浮层

// el {Element}

function autoCenter(el) {

// 获得可视区域的宽和高

var bodyW = document.documentElement.clientWidth;

var bodyH = document.documentElement.clientHeight;

// 获得元素 el 的宽和高

var elW = el.offsetWidth;

var elH = el.offsetHeight;

// 设置元素的 style 样式

el.style.left = (bodyW - elW) / 2 + 'px';

el.style.top = (bodyH - elH) / 2 + 'px';

}

// 扩展元素到整个可视区域 -- 遮罩层

// el {Element}

function fillToBody(el) {

// 将元素的宽和高设置的和可视区域一样

el.style.width = document.documentElement.clientWidth + 'px';

el.style.height = document.documentElement.clientHeight + 'px';

}

// 定义全局变量

var mouseOffsetX = 0;

var mouseOffsetY = 0;

var isDragging = false;

// 鼠标事件1 -- 在标题栏上按下

// 计算鼠标相对拖拽元素的的左上角的坐标，并且标记元素为可拖动

g('dialogTitle').addEventListener('mousedown', function(e) {

var e = e || window.event;

// 用鼠标按下时的坐标减去 dialog 的左上角坐标

mouseOffsetX = e.pageX - g('dialog').offsetLeft;

mouseOffsetY = e.pageY - g('dialog').offsetTop;

isDragging = true;

});

// 鼠标事件2 -- 鼠标移动

document.onmousemove = function(e) {

var e = e || window.event;

// 鼠标当前位置

var mouseX = e.pageX;

var mouseY = e.pageY;

// 鼠标从单击时至当前时刻移动的距离

var moveX = 0;

var moveY = 0;

if (isDragging === true) {

moveX = mouseX - mouseOffsetX;

moveY = mouseY - mouseOffsetY;

// 范围限定

// moveX > 0 且 moveX < (页面最大宽度 - 浮层宽度)

// moveY > 0 且 moveY < (页面最大宽度 - 浮层高度)

var pageWidth = document.documentElement.clientWidth;

var pageHeight = document.documentElement.clientHeight;

// 登录浮层的宽、高

var dialogWidth = g('dialog').offsetWidth;

var dialogHeight = g('dialog').offsetHeight;

var maxX = pageWidth - dialogWidth;

var maxY = pageHeight - dialogHeight;

moveX = Math.min(maxX, Math.max(0, moveX));

moveY = Math.min(maxY, Math.max(0, moveY));

g('dialog').style.left = moveX + 'px';

g('dialog').style.top = moveY + 'px';

}

};

// 鼠标事件3 -- 鼠标松开

document.onmouseup = function() {

isDragging = false;

};

// 展现登录浮层

function showDialog() {

g('dialog').style.display = 'block';

g('mask').style.display = 'block';

autoCenter(g('dialog'));

fillToBody(g('mask'));

}

// 隐藏登录浮层

function hideDialog() {

g('dialog').style.display = 'none';

g('mask').style.display = 'none';

}

window.onresize = function() {

autoCenter(g('dialog'));

fillToBody(g('mask'));

};

showDialog();

autoCenter(g('dialog'));

</script>

</body>

</html>

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