今天我们要来介绍一款基于jQuery功能非常强大的图片裁剪插件，这款jQuery图片裁剪插件可以选择裁剪框的尺寸比例，可以设置高宽尺寸，同时可以设置图片翻转角度，当然也支持图片的缩放，裁剪框也可以用鼠标拖动。效果图如下：

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来看看实现的代码，这里我们主要来看JavaScript代码

获取图片的Canvas画布：

function getSourceCanvas(image, data) {
    var canvas = $('<canvas>')[0],
        context = canvas.getContext('2d'),
        width = data.naturalWidth,
        height = data.naturalHeight,
        rotate = data.rotate,
        rotated = getRotatedSizes({
          width: width,
          height: height,
          degree: rotate
        });

    if (rotate) {
      canvas.width = rotated.width;
      canvas.height = rotated.height;
      context.save();
      context.translate(rotated.width / 2, rotated.height / 2);
      context.rotate(rotate * Math.PI / 180);
      context.drawImage(image, -width / 2, -height / 2, width, height);
      context.restore();
    } else {
      canvas.width = width;
      canvas.height = height;
      context.drawImage(image, 0, 0, width, height);
    }

    return canvas;
  }

加载图片：

prototype.load = function (url) {
    var options = this.options,
        $this = this.$element,
        crossOrigin,
        bustCacheUrl,
        buildEvent,
        $clone;

    if (!url) {
      if ($this.is('img')) {
        if (!$this.attr('src')) {
          return;
        }

        url = $this.prop('src');
      } else if ($this.is('canvas') && SUPPORT_CANVAS) {
        url = $this[0].toDataURL();
      }
    }

    if (!url) {
      return;
    }

    buildEvent = $.Event(EVENT_BUILD);
    $this.one(EVENT_BUILD, options.build).trigger(buildEvent); // Only trigger once

    if (buildEvent.isDefaultPrevented()) {
      return;
    }

    if (options.checkImageOrigin && isCrossOriginURL(url)) {
      crossOrigin = 'anonymous';

      if (!$this.prop('crossOrigin')) { // Only when there was not a "crossOrigin" property
        bustCacheUrl = addTimestamp(url); // Bust cache (#148)
      }
    }

    this.$clone = $clone = $('<img>');

    $clone.one('load', $.proxy(function () {
      var naturalWidth = $clone.prop('naturalWidth') || $clone.width(),
          naturalHeight = $clone.prop('naturalHeight') || $clone.height();

      this.image = {
        naturalWidth: naturalWidth,
        naturalHeight: naturalHeight,
        aspectRatio: naturalWidth / naturalHeight,
        rotate: 0
      };

      this.url = url;
      this.ready = true;
      this.build();
    }, this)).one('error', function () {
      $clone.remove();
    }).attr({
      src: bustCacheUrl || url,
      crossOrigin: crossOrigin
    });

    // Hide and insert into the document
    $clone.addClass(CLASS_HIDE).insertAfter($this);
  };

预览截图：

prototype.initPreview = function () {
    var url = this.url;

    this.$preview = $(this.options.preview);
    this.$viewBox.html('<img src="' + url + '">');

    // Override img element styles
    // Add `display:block` to avoid margin top issue (Occur only when margin-top <= -height)
    this.$preview.each(function () {
      var $this = $(this);

      $this.data(CROPPER_PREVIEW, {
        width: $this.width(),
        height: $this.height(),
        original: $this.html()
      }).html('<img src="' + url + '" style="display:block;width:100%;min-width:0!important;min-height:0!important;max-width:none!important;max-height:none!important;image-orientation: 0deg!important">');
    });
  };

via：http://www.w2bc.com/Article/37726

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