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
}
}
function compress (img, Orientation) {
let canvas = document.createElement('canvas')
let ctx = canvas.getContext('2d')
// 瓦片canvas
let tCanvas = document.createElement('canvas')
let tctx = tCanvas.getContext('2d')
let initSize = img.src.length
let width = img.width
let height = img.height
// 如果图片大于四百万像素，计算压缩比并将大小压至400万以下
let ratio
if ((ratio = width * height / 4000000) > 1) {
console.log('大于400万像素')
ratio = Math.sqrt(ratio)
width /= ratio
height /= ratio
} else {
ratio = 1
}
canvas.width = width
canvas.height = height
// 铺底色
ctx.fillStyle = '#fff'
ctx.fillRect(0, 0, canvas.width, canvas.height)
// 如果图片像素大于100万则使用瓦片绘制
let count
if ((count = width * height / 1000000) > 1) {
console.log('超过100W像素')
count = ~~(Math.sqrt(count) + 1) // 计算要分成多少块瓦片
// 计算每块瓦片的宽和高
let nw = ~~(width / count)
let nh = ~~(height / count)
console.log(nw, nh)
tCanvas.width = nw
tCanvas.height = nh
for (let i = 0; i < count; i++) {
for (let 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
rotateImg(img, 'left', canvas)
break
case 8:// 需要逆时针（向右）90度旋转
rotateImg(img, 'right', canvas)
break
case 3:// 需要180度旋转
rotateImg(img, 'right', canvas)// 转两次
rotateImg(img, 'right', canvas)
break
}
}
// 进行最小压缩
let ndata = canvas.toDataURL('image/jpeg', 0.1)
console.log('压缩前：' + initSize)
console.log('压缩后：' + ndata.length)
console.log('压缩率：' + ~~(100 * (initSize - ndata.length) / initSize) + '%')
tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0
return ndata
}
export default compress