Created
February 25, 2020 05:56
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画像の向きを修正するやつ(主にスマホ向け)
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/** | |
* 画像の向きを修正する | |
* https://stackoverflow.com/questions/20600800/js-client-side-exif-orientation-rotate-and-mirror-jpeg-images | |
* @param {(File|Blob)} file 画像 | |
* @return {Promise.<{src, width, height}>} | |
*/ | |
export function getDataUrl(file) { | |
return new Promise(resolve => { | |
const callback = function(srcOrientation) { | |
const reader2 = new FileReader(); | |
reader2.onload = function(e) { | |
const srcBase64 = e.target.result; | |
const img = new Image(); | |
img.onload = function() { | |
const width = img.width, | |
height = img.height, | |
canvas = document.createElement('canvas'), | |
ctx = canvas.getContext('2d'); | |
// set proper canvas dimensions before transform & export | |
if ([5, 6, 7, 8].includes(srcOrientation)) { | |
canvas.width = height; | |
canvas.height = width; | |
} else { | |
canvas.width = width; | |
canvas.height = height; | |
} | |
// transform context before drawing image | |
switch (srcOrientation) { | |
case 2: | |
ctx.transform(-1, 0, 0, 1, width, 0); | |
break; | |
case 3: | |
ctx.transform(-1, 0, 0, -1, width, height); | |
break; | |
case 4: | |
ctx.transform(1, 0, 0, -1, 0, height); | |
break; | |
case 5: | |
ctx.transform(0, 1, 1, 0, 0, 0); | |
break; | |
case 6: | |
ctx.transform(0, 1, -1, 0, height, 0); | |
break; | |
case 7: | |
ctx.transform(0, -1, -1, 0, height, width); | |
break; | |
case 8: | |
ctx.transform(0, -1, 1, 0, 0, width); | |
break; | |
default: | |
break; | |
} | |
// draw image | |
ctx.drawImage(img, 0, 0); | |
// export | |
resolve({ | |
src: canvas.toDataURL(), | |
width, | |
height | |
}); | |
}; | |
img.src = srcBase64; | |
}; | |
reader2.readAsDataURL(file); | |
}; | |
const reader = new FileReader(); | |
reader.onload = function(e) { | |
const view = new DataView(e.target.result); | |
if (view.getUint16(0, false) != 0xffd8) return callback(-2); | |
let length = view.byteLength, | |
offset = 2; | |
while (offset < length) { | |
const marker = view.getUint16(offset, false); | |
offset += 2; | |
if (marker == 0xffe1) { | |
if (view.getUint32((offset += 2), false) != 0x45786966) | |
return callback(-1); | |
const little = view.getUint16((offset += 6), false) == 0x4949; | |
offset += view.getUint32(offset + 4, little); | |
const tags = view.getUint16(offset, little); | |
offset += 2; | |
for (let i = 0; i < tags; i++) | |
if (view.getUint16(offset + i * 12, little) == 0x0112) | |
return callback(view.getUint16(offset + i * 12 + 8, little)); | |
} else if ((marker & 0xff00) != 0xff00) break; | |
else offset += view.getUint16(offset, false); | |
} | |
return callback(-1); | |
}; | |
reader.readAsArrayBuffer(file); | |
}); | |
} |
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