一、前言：
上一篇随笔中已经把拖动程序完成了，这篇主要把缩放程序完成，后面合并后可以做成一个图片裁剪的功能
简易缩放程序DEMO：http://jsfiddle.net/UN99R/
限制缩放程序DEMO：http://jsfiddle.net/kHWQZ/
二、设计思路：
1、在一个可以缩放元素中，共有8个触发点(上、下、左、右、左上、右上、左下、右下)，首先分别设置好它们的CSS属性cursor值。
2、同拖放程序一样，在触发点上绑定鼠标按下事件，在文档(document)上绑定鼠标移动、弹起事件处理程序，在移动事件中，完成拖放元素css的操作，
在鼠标弹起事件中，解绑移动事件处理程序。
主要难点：在于如何处理拖放元素的CSS属性
三、源码实现细节：
在8个触发点的事件处理程序中，diffX, diffY 分别获取的是鼠标在移动与按下过程时指针的差值
var diffX = e.clientX - clientX, // 负数代表向左移动，反之向右
diffY = e.clientY - clientY; // 负数代表想上移动，反之向下
在鼠标按下事件处理中，w, h, l, t 分别记录的是拖放元素的width, height, left, top 属性值，下面讲一下鼠标移动处理程序
举一个示例：
up事件程序代码：
up = function(e){
var diffY = e.clientY - clientY;
$target.css({
height: h - diffY + 'px',
top: t + Math.min(diffY, h) + 'px'
});
e.preventDefault();
};
1、在up事件程序中，拖放元素变动的是height, top属性；
2、如果鼠标向上移动，diffY为负数，而height应增，因此 height = h - diffY, top则相反，top = t + diffY;
3、反之，diffY为正数，而height应减，因此 height = h - diffY, top = t + diffY;
4、为了让top值不为负数，top = t + Math.min(diffY, h);
最后阻止默认浏览器事件，避免鼠标拖动过程中出现禁止icon
处理完up事件后，其他down, left, right事件处理同理，而后 upLeft, upRight, downLeft, downRight 这些事件处理都是在叠加前四个事件处理就行了
主程序代码：
jQuery.fn.extend({
/**
* Autor: 博客园华子yjh 2014/02/26
*/
resize: function(options) {
var controlSelector = '.cursor-north, .cursor-south, .cursor-west, .cursor-east,' +
'.cursor-north-west, .cursor-north-east, .cursor-south-west, .cursor-south-east';
$(this).each(function(){
var
// 上、下、左、右、左上、右上、左下、右下 八个点的鼠标拖动时的事件处理程序
up, down, left, right, upLeft, upRight, downLeft, downRight,
// 鼠标拖动时的事件处理程序
handleEvent,
// 记录鼠标按下时鼠标的位置
clientX, clientY,
// 记录鼠标按下时元素的大小及位置
w, h, l, t,
// 目标元素
$target = $(this), self = this;
up = function(e){
var diffY = e.clientY - clientY;
$target.css({
height: h - diffY + 'px',
top: t + Math.min(diffY, h) + 'px'
});
e.preventDefault();
};
down = function(e){
var diffY = e.clientY - clientY;
$target.css({
height: h + diffY + 'px'
});
e.preventDefault();
};
left = function(e){
var diffX = e.clientX - clientX;
$target.css({
width: w - diffX + 'px',
left: l + Math.min(diffX, w) + 'px'
});
e.preventDefault();
};
right = function(e){
var diffX = e.clientX - clientX;
$target.css({
width: w + diffX + 'px'
});
e.preventDefault();
};
upLeft = function(e){
var diffX = e.clientX - clientX,
diffY = e.clientY - clientY;
$target.css({
height: h - diffY + 'px',
top: t + Math.min(diffY, h) + 'px',
width: w - diffX + 'px',
left: l + Math.min(diffX, w) + 'px'
});
e.preventDefault();
};
upRight = function(e){
var diffX = e.clientX - clientX,
diffY = e.clientY - clientY;
$target.css({
height: h - diffY + 'px',
top: t + Math.min(diffY, h) + 'px',
width: w + diffX + 'px'
});
e.preventDefault();
};
downLeft = function(e){
var diffX = e.clientX - clientX,
diffY = e.clientY - clientY;
$target.css({
width: w - diffX + 'px',
left: l + Math.min(diffX, w) + 'px',
height: h + diffY + 'px'
});
e.preventDefault();
};
downRight = function(e){
var diffX = e.clientX - clientX,
diffY = e.clientY - clientY;
$target.css({
width: w + diffX + 'px',
height: h + diffY + 'px'
});
e.preventDefault();
};
$target.delegate(controlSelector, 'mousedown', function(e){
var className = $(this).attr('class');
clientX = e.clientX;
clientY = e.clientY;
w = $target.width(),
h = $target.height(),
l = $target.get(0).offsetLeft,
t = $target.get(0).offsetTop;
// 根据触发元素的className选择要触发的事件处理程序
switch (className) {
case 'cursor-north':
handleEvent = up;
break;
case 'cursor-south':
handleEvent = down;
break;
case 'cursor-west':
handleEvent = left;
break;
case 'cursor-east':
handleEvent = right;
break;
case 'cursor-north-west':
handleEvent = upLeft;
break;
case 'cursor-north-east':
handleEvent = upRight;
break;
case 'cursor-south-west':
handleEvent = downLeft;
break;
case 'cursor-south-east':
handleEvent = downRight;
break;
default:
break;
}
$(document)
.bind('mousemove', handleEvent)
.bind('mouseup', function(){
$(document).unbind('mousemove', handleEvent);
$target.removeData('data-resize'); // 移除标志
});
$target.data('data-resize', true); // 缓存标志
});
});
return this;
}
});
带限制范围缩放代码：
jQuery.fn.extend({
/**
* Autor: 博客园华子yjh 2014/02/26
*/
resize: function(options) {
var defaultOptions, boundaryElem, limitObj, controlSelector;
controlSelector = '.cursor-north, .cursor-south, .cursor-west, .cursor-east, .cursor-north-west, .cursor-north-east, .cursor-south-west, .cursor-south-east';
defaultOptions = { // 默认配置项
boundaryElem: 'body' // 边界容器
};
options = jQuery.extend( defaultOptions, options || {} );
boundaryElem = $(options.boundaryElem).get(0);
limitObj = {
_left: boundaryElem.offsetLeft,
_top: boundaryElem.offsetTop,
_right: boundaryElem.offsetLeft + boundaryElem.clientWidth,
_bottom: boundaryElem.offsetTop + boundaryElem.clientHeight
};
$(this).each(function(){
var up, down, left, right, upLeft, upRight, downLeft, downRight,
clientX, clientY, w, h, l, t,
$target = $(this), self = this,
handleEvent = function(){};
up = function(e){
var diffY = e.clientY - clientY;
$target.css({
height: h + Math.min(0 - diffY, t) + 'px',
top: Math.max(t + Math.min(diffY, h), 0) + 'px'
});
e.preventDefault();
};
down = function(e){
var diffY = e.clientY - clientY;
$target.css({
height: h + Math.min(diffY, limitObj._bottom - limitObj._top - t - h) + 'px'
});
e.preventDefault();
};
left = function(e){
var diffX = e.clientX - clientX;
$target.css({
width: w + Math.min(0- diffX, l) + 'px',
left: Math.max(l + Math.min(diffX, w), 0) + 'px'
});
e.preventDefault();
};
right = function(e){
var diffX = e.clientX - clientX;
$target.css({
width: w + Math.min(diffX, limitObj._right - limitObj._left - l - w) + 'px'
});
e.preventDefault();
};
upLeft = function(e){
var diffX = e.clientX - clientX,
diffY = e.clientY - clientY;
$target.css({
height: h + Math.min(0 - diffY, t) + 'px',
top: Math.max(t + Math.min(diffY, h), 0) + 'px',
width: w + Math.min(0- diffX, l) + 'px',
left: Math.max(l + Math.min(diffX, w), 0) + 'px'
});
e.preventDefault();
};
upRight = function(e){
var diffX = e.clientX - clientX,
diffY = e.clientY - clientY;
$target.css({
height: h + Math.min(0 - diffY, t) + 'px',
top: Math.max(t + Math.min(diffY, h), 0) + 'px',
width: w + Math.min(diffX, limitObj._right - limitObj._left - l - w) + 'px'
});
e.preventDefault();
};
downLeft = function(e){
var diffX = e.clientX - clientX,
diffY = e.clientY - clientY;
$target.css({
width: w + Math.min(0- diffX, l) + 'px',
left: Math.max(l + Math.min(diffX, w), 0) + 'px',
height: h + Math.min(diffY, limitObj._bottom - limitObj._top - t - h) + 'px'
});
e.preventDefault();
};
downRight = function(e){
var diffX = e.clientX - clientX,
diffY = e.clientY - clientY;
$target.css({
width: w + Math.min(diffX, limitObj._right - limitObj._left - l - w) + 'px',
height: h + Math.min(diffY, limitObj._bottom - limitObj._top - t - h) + 'px'
});
e.preventDefault();
};
$target.delegate(controlSelector, 'mousedown', function(e){
var className = $(this).attr('class');
clientX = e.clientX;
clientY = e.clientY;
w = $target.width(),
h = $target.height(),
l = $target.get(0).offsetLeft,
t = $target.get(0).offsetTop;
switch (className) {
case 'cursor-north':
handleEvent = up;
break;
case 'cursor-south':
handleEvent = down;
break;
case 'cursor-west':
handleEvent = left;
break;
case 'cursor-east':
handleEvent = right;
break;
case 'cursor-north-west':
handleEvent = upLeft;
break;
case 'cursor-north-east':
handleEvent = upRight;
break;
case 'cursor-south-west':
handleEvent = downLeft;
break;
case 'cursor-south-east':
handleEvent = downRight;
break;
default:
break;
}
$(document)
.bind('mousemove', handleEvent)
.bind('mouseup', function(){
$(document).unbind('mousemove', handleEvent);
$target.removeData('data-resize'); // 移除标志
});
$target.data('data-resize', true); // 缓存标志
})
});
return this;
}
});
PS: 如有描述错误，请帮忙指正，如果你们有不明白的地方也可以发邮件给我，