/**
* 使用canvas压缩照片
* @param img 需要压缩的照片
* @param Orientation 照片原始方向
* @returns {string} base64格式照片数据
*/
function compress(img, Orientation) {
var canvas =document.createElement("canvas");
var ctx = canvas.getContext('2d');
//瓦片canvas
var tCanvas =document.createElement("canvas");
var tctx = tCanvas.getContext("2d");
// var initSize = img.src.length;
var width = img.width;
var height = img.height;
//图片像素大于400万像素，计算压缩到400万以下
var ratio;
if ((ratio = width * height /4000000) >1) {
ratio = Math.sqrt(ratio);
width /= ratio;
height /= ratio;
}else {
ratio =1;
}
canvas.width = width;
canvas.height = height;
ctx.fillStyle ="#fff";
ctx.fillRect(0, 0, canvas.width, canvas.height);
//如果图片太大(大于100万像素)则使用瓦片绘制
var count;
if ((count = width * height /1000000 >1)) {
count = ~~(Math.sqrt(count) +1);//计算分成的瓦片数
var nw = ~~(width / count);
var nh = ~~(height / count);
tCanvas.width = nw;
tCanvas.height = nh;
for (var i =0; i < count; i++) {
for (var j =0; j < count; j++) {
tctx.drawImage(img, i * nw * ratio, j * nh * ratio, nw * ratio, nh * ratio, 0, 0, nw, nh);
ctx.drawImage(tCanvas, i * nw, j * nh, nw, nh)
}
}
}else {
ctx.drawImage(img, 0, 0, width, height)
}
//修复ios上传图片的时候 被旋转的问题
if (Orientation !="" && Orientation !=1) {
switch (Orientation) {
case 6://需要顺时针（向左）90度旋转
this.rotateImg(img, "left", canvas);
break;
case 8://需要逆时针（向右）90度旋转
this.rotateImg(img, "right", canvas);
break;
case 3://需要180度旋转
this.rotateImg(img, "right", canvas); //转两次
this.rotateImg(img, "right", canvas);
break;
}
}
//进行最小压缩
var ndata = canvas.toDataURL('image/jpeg', 0.1);
tCanvas.width = tCanvas.height = canvas.width = canvas.height =0;
return ndata;
}
/**
* 旋转照片
* @param img 需要旋转的照片
* @param direction 旋转方向
* @param canvas 绘图canvas
*/
function rotateImg(img, direction, canvas) {
//最小与最大旋转方向，图片旋转4次后回到原方向
const min_step =0;
const max_step =3;
if (img ==null)return;
//img的高度和宽度不能在img元素隐藏后获取，否则会出错
let height = img.height;
let width = img.width;
let step =2;
if (step ==null) {
step = min_step;
}
if (direction =="right") {
step++;
//旋转到原位置，即超过最大值
step > max_step && (step = min_step);
}else {
step--;
step < min_step && (step = max_step);
}
//旋转角度以弧度值为参数
let degree = (step *90 * Math.PI) /180;
let ctx = canvas.getContext("2d");
switch (step) {
case 0:
canvas.width = width;
canvas.height = height;
ctx.drawImage(img, 0, 0);
break;
case 1:
canvas.width = height;
canvas.height = width;
ctx.rotate(degree);
ctx.drawImage(img, 0, -height);
break;
case 2:
canvas.width = width;
canvas.height = height;
ctx.rotate(degree);
ctx.drawImage(img, -width, -height);
break;
case 3:
canvas.width = height;
canvas.height = width;
ctx.rotate(degree);
ctx.drawImage(img, -width, 0);
break;
}
}