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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;
}
},
//将base64转换为文件
dataURLtoFile(dataurl) {
var arr = dataurl.split(","),
bstr = atob(arr[1]),
n = bstr.length,
u8arr = new Uint8Array(n);
while (n--) {
u8arr[n] = bstr.charCodeAt(n);
}
return new File([u8arr], this.files.name, {
type: this.files.type
});
},
//这里写接口
async postImg() {
let file = this.dataURLtoFile(this.headerImage);
let formData = new window.FormData();
formData.append("file", file);
toast_loding(this, "图片上传中···");
try {
let res = await util.ajax.post(this.upImgUrl, formData, {
headers: {
"Content-Type": "multipart/form-data"
}
});
} catch (e) {
console.log(e);
}
}
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参考：https://www.cnblogs.com/lvshaonan/p/8547676.html
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