Node.js 使用gm处理图像

var fs = require(‘fs‘)
    , gm = require(‘gm‘);

var imageParameter = require(‘../models/ImageParameter‘);

exports.createImage = function (oriUrl,descUrl,obj,successFn) {
    var outputImage = gm(oriUrl);
    var m = imageParameter.getMode();
    outputImage.size(function(err, ori) {
        //设置图片质量格式
        outputImage = outputImage.quality(obj.quantity).setFormat(obj.format);
        //调整尺寸
        switch(obj.mode){
            case m.HW://指定高宽缩放（可能变形）
                outputImage = outputImage.resize(obj.width, obj.height,"!");
                break;
            case m.W://指定宽，高按比例
                if(obj.width >= ori.width){
                    outputImage = outputImage.resize(ori.width, null);
                }else{
                    outputImage = outputImage.resize(obj.width, null);
                }
                break;
            case m.H://指定高，宽按比例
                if(obj.height >= ori.height){
                    outputImage = outputImage.resize(null, ori.height);
                }else{
                    outputImage = outputImage.resize(null, obj.height);
                }
                break;
            case m.CUT://裁剪（不变形）
                var toHeight = ori.width;
                var toWidth = ori.height;
                var x = 0;
                var y = 0;
                if(ori.width >= obj.width && ori.height >= obj.height){
                    //以高为基准
                    if(ori.width/ori.height >= obj.width/obj.height){
                       toHeight = ori.height;
                       toWidth  = ori.height * obj.width / obj.height;
                       x= (ori.width -toWidth)/2;
                       y=0;
                    }else{
                        toWidth  = ori.width;
                        toHeight = ori.width * obj.height / obj.width;
                        x= 0;
                        y= (ori.height -toHeight)/2;
                    }
                }else{
                    x = (ori.width - obj.width)/2;
                    y = (ori.height - obj.height)/2;
                    toWidth = obj.width;
                    toHeight = obj.height;
                }
                outputImage= outputImage.crop(toWidth,toHeight, x, y);
                break;
            case m.FIT://固定
                if(obj.width >= ori.width || obj.height >= ori.height){
                    outputImage = outputImage.resize(ori.width, ori.height);
                }else{
                    if(obj.width/ori.width > obj.height/ori.height){
                        outputImage = outputImage.resize(obj.width, null);
                    }else{
                        outputImage = outputImage.resize(null, obj.height);
                    }
                }
                break;
            default:
                break;
        }
        //写入图片
        outputImage.write(descUrl, function (err) {
            if (!err){
                successFn();
            }
        });
        }
    );

}