JavaScript简易缩放程序
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，
