微信小程序 图片等比例缩放（图片自适应屏幕）

<!--index.wxml--> 
<!--图片宽大于屏幕宽--> 
<image style="width: {{imagewidth}}px; height: {{imageheight}}px;" src="{{imagefirstsrc}}" bindload="imageLoad"></image> 
<!--图片高大于屏幕高--> 
<!--<image style="width: {{imagewidth}}px; height: {{imageheight}}px;" src="{{imagesecondsrc}}" bindload="imageLoad"></image>--> 
<!--图片宽高大于屏幕宽高--> 
<!--<image style="width: {{imagewidth}}px; height: {{imageheight}}px;" src="{{imagethirdsrc}}" bindload="imageLoad"></image>--> 

//index.js 
//获取应用实例 
var imageUtil = require('../../utils/util.js'); 
var app = getApp() 
Page({ 
 data: { 
  imagefirstsrc: 'http://bpic.588ku.com/back_pic/00/03/85/1656205138bbe2d.png',//图片链接 
  imagesecondsrc: 'http://bpic.588ku.com/back_pic/04/07/63/28581203949ca9d.jpg!/fw/400/quality/90/unsharp/true/compress/true',//图片链接 
  imagethirdsrc:'http://img1.gtimg.com/ent/pics/hv1/13/71/2061/134034643.jpg', 
  imagewidth: 0,//缩放后的宽 
  imageheight: 0,//缩放后的高 
 
 }, 
 onLoad: function () { 
 }, 
 imageLoad: function (e) { 
  var imageSize = imageUtil.imageUtil(e) 
  this.setData({ 
   imagewidth: imageSize.imageWidth, 
   imageheight: imageSize.imageHeight 
  }) 
 } 
}) 

//util.js 
function imageUtil(e) { 
 var imageSize = {}; 
 var originalWidth = e.detail.width;//图片原始宽 
 var originalHeight = e.detail.height;//图片原始高 
 var originalScale = originalHeight/originalWidth;//图片高宽比 
 console.log('originalWidth: ' + originalWidth) 
 console.log('originalHeight: ' + originalHeight) 
 //获取屏幕宽高 
 wx.getSystemInfo({ 
  success: function (res) { 
   var windowWidth = res.windowWidth; 
   var windowHeight = res.windowHeight; 
   var windowscale = windowHeight/windowWidth;//屏幕高宽比 
   console.log('windowWidth: ' + windowWidth) 
   console.log('windowHeight: ' + windowHeight) 
   if(originalScale < windowscale){//图片高宽比小于屏幕高宽比 
    //图片缩放后的宽为屏幕宽 
     imageSize.imageWidth = windowWidth; 
     imageSize.imageHeight = (windowWidth * originalHeight) / originalWidth; 
   }else{//图片高宽比大于屏幕高宽比 
    //图片缩放后的高为屏幕高 
     imageSize.imageHeight = windowHeight; 
     imageSize.imageWidth = (windowHeight * originalWidth) / originalHeight; 
   } 
    
  } 
 }) 
 console.log('缩放后的宽: ' + imageSize.imageWidth) 
 console.log('缩放后的高: ' + imageSize.imageHeight) 
 return imageSize; 
} 
 
module.exports = { 
 imageUtil: imageUtil 
}