功能分两部分:展示、提交
一期的时候,用户预览图片,直接提交到后台。但是发现如果图片太大,还要进行二次处理,还会降低接口相应速度等原因。所以要对图片进行压缩。
压缩原理:选择图片后,利用canvas的drawImage方法重新定义图片大小,再利用canvasToTempFilePath方法下载到缩小后图片。
// 利用绝对定位 隐藏canvas
<canvas canvas-id="photo_canvas" style="width:{{canvasWidth}}px;height:{{canvasHeight}}px;position: absolute;left:-300px;top:-300px;"></canvas>
wx.chooseImage({
count: 1,
sizeType: ['compressed'],
success: function (photo) {
wx.getImageInfo({
src: photo.tempFilePaths[0],
success: function(res){
var ctx = wx.createCanvasContext('photo_canvas');
var ratio = 2;
var canvasWidth = res.width
var canvasHeight = res.height;
// 保证宽高均在200以内
while (canvasWidth > 200 || canvasHeight > 200){
//比例取整
canvasWidth = Math.trunc(res.width / ratio)
canvasHeight = Math.trunc(res.height / ratio)
ratio++;
}
_this.setData({
canvasWidth: canvasWidth,
canvasHeight: canvasHeight
})//设置canvas尺寸
ctx.drawImage(photo.tempFilePaths[0], 0, 0, canvasWidth, canvasHeight)
ctx.draw()
//下载canvas图片
setTimeout(function(){
wx.canvasToTempFilePath({
canvasId: 'photo_canvas',
success: function (res) {
console.log(res.tempFilePath)
},
fail: function (error) {
console.log(error)
}
})
},100)
},
fail: function(error){
console.log(error)
}
})
},
error: function (res) {
console.log(res);
}
})